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The structure of a small globular protein shown as a space-filling atomic model (a), as a wire model with the chemically regular backbone outlined by dark line and various side chains by light lines (b), and as a ribbon diagram that outlines the backbone fold and the secondary structures (c). The secondary structures are presented by two α -helices (the turns within each helix being fasten together by backbone-backbone hydrogen bonds) and three extended β -strands (shown as arrows), which, being fasten together by backbone-backbone hydrogen bonds between them, form a single β -sheet. This and the other drawings of protein structures are done using their Protein Data Bank [7] coordinates by the MOLSCRIPT [8] and Insight II (Accelrys Inc.) programs. The drawing is adapted from [9]. 

The structure of a small globular protein shown as a space-filling atomic model (a), as a wire model with the chemically regular backbone outlined by dark line and various side chains by light lines (b), and as a ribbon diagram that outlines the backbone fold and the secondary structures (c). The secondary structures are presented by two α -helices (the turns within each helix being fasten together by backbone-backbone hydrogen bonds) and three extended β -strands (shown as arrows), which, being fasten together by backbone-backbone hydrogen bonds between them, form a single β -sheet. This and the other drawings of protein structures are done using their Protein Data Bank [7] coordinates by the MOLSCRIPT [8] and Insight II (Accelrys Inc.) programs. The drawing is adapted from [9]. 

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Protein physics is grounded on three fundamental experimental facts: protein, this long heteropolymer, has a well defined compact three-dimensional structure; this structure can spontaneously arise from the unfolded protein chain in appropriate environment; and this structure is separated from the unfolded state of the chain by the “all-or-none” ph...

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... are molecular machines, building blocks, and arms of a living cell. Enormous variety of protein functions is based on their high specificity for the treated molecules that resembles the key- and-lock relationship. This specificity requires a definite, stable and rather rigid spatial structure of the protein, existing at least at the moment of its interaction with the treated molecule. Protein is an amino acid heteropolymer with unique (for each protein) sequence of links. In an “oper- ating” protein its chain is folded in a definite (“native”) structure ( Fig. 1). In the late 1950s, Perutz and Kendrew solved the first structures of protein crystals and demonstrated highly intricate protein spatial structures [1,2]. Later, the identity (to small fluctuations) of structures in a crystal and in solution was demonstrated by NMR spectroscopy [3] for various proteins. Protein physics is grounded on three fundamental experimental facts: (i) proteins have, as a rule, well defined three-dimensional (3D) structures [1–3]; (ii) protein chains are capable of self-organization, i.e., they form their native structures spontaneously in appropriate environment [4,5] (unless their chains are too modified chemically after the initial folding in the cell), and (iii) the native state of many of these proteins is separated from the unfolded state of the chain by the “all-or-none” transition [6], which is a microscopic analog of the first order phase transition. This phase transition ensures robustness of protein structure and therefore of its action. Proteins “live” under various environmental conditions leaving an obvious mark on their structures. Fibrous proteins (Fig. 2a) form vast and almost water-free aggregates; their structure is usually highly hydrogen-bonded, highly regular and non-compact (as far as separate chains are concerned). Membrane proteins (Fig. 2b) are imbedded into water-lacking membranes. Their intramembrane portions are also highly regular and highly hydrogen-bonded, but restricted in size by the membrane thickness ( ∼ 40 Å). Water-soluble globular proteins (Figs. 1 and 2c) are less regular (especially at the protein/water interface). Their compact structure is maintained by interactions of the chain with itself and sometimes with various other molecules (co-factors). Typical globule includes 50–200 amino acids; its typical diameter is 25–40 Å. Larger globular proteins consist of a few compact sub-globules, or “domains”. Experimental and theoretical physics of protein folding is a huge and (by now) well developed field, which cannot be covered in a single review or even book. In the wide sense, the term “protein folding” includes structural, thermodynamic and kinetic aspects of transition of initially unfolded protein chain into its final native 3D structure, as well as structural transitions and dynamics of this structure in a working protein. We, however, will use this term in a more narrow sense (which is sometimes called “protein folding problem of the first order”) and focus upon kinetic and structural aspects of transition of initially unfolded protein chain into its final native 3D structure only. Thermodynamic aspects of this transition will be touched upon very briefly, and only in so far as they form a basis of folding kinetics. Protein dynamics, which is so important in protein functioning, and intriguing problems of protein structure prediction (sometimes called “protein folding problem of the first order”, or “folding in silico”) will be not considered at all. The aim of this paper, based on some chapters of a recent book “Protein Physics” [9], is to overview modern understanding of physical principles of self-organization (“folding”) of protein structures. It, undoubtedly, reflects the authors’ preferences and tastes, and an experienced reader may probably find that it is biased towards the authors’ own work. We will overview the main experimental facts and simple, intelligible, mostly phenomenological theoretical models of protein folding, and we will consider mostly single-domain water-soluble globular proteins, whose structure and especially folding are studied much better than those of the others. In a living cell, protein is synthesized by a ribosome that makes a protein chain (Fig. 3) from amino acids (brought by adaptor tRNAs). There are 20 main natural amino acids; positions of their residues in the protein chain are encoded by mRNA encoded by gene. The ribosome synthesizes protein chain residue by residue, from its N- to C-end, and not quite uni- formly: there are temporary rests of the synthesis at the “rare” codons (they correspond to tRNAs which are rare in the cell, and these codons are rare in the cell’s mRNAs, too). It is assumed that the pauses may correspond to the boundaries of structural domains that can help a quiet maturation of the domain structures. The biosynthesis takes about a minute and yielding of a “ready” folded protein lasts as long: the experiment does not see any difference [11,12]. Some enzymes, like prolyl-peptide- or disulfide-isomerases accelerate in vivo folding. They catalyze slow, if unaided, trans ↔ cis conversions of the backbone conformation of some amino acids (prolines) and formation (and decay) of S–S chemical bonds formed by side chains of amino acids cysteines. Protein chains fold under protection of special proteins, chaperons. Chaperones are the cell’s trouble- shooters that fight the aggregation of nascent proteins, since, in a cell, folding takes place in a highly crowded molecular ...
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... is an amino acid heteropolymer with unique (for each protein) sequence of links. In an "oper- ating" protein its chain is folded in a definite ("native") structure (Fig. 1). In the late 1950s, Perutz and Kendrew solved the first structures of protein crystals and demonstrated highly intricate protein spatial structures [1,2]. Later, the identity (to small fluctuations) of structures in a crystal and in solution was demonstrated by NMR spectroscopy [3] for various ...
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... the "Levinthal paradox" and to show that the most stable chain fold of protein chain can be found within a reasonable time, we can, to a first approximation, consider only the rate of the "all-or-none" transition between the coil and the most stable structure, assuming that the amino acid sequence of the chain provides a sufficient "energy gap" (Fig. 10). And we may consider only the case when the most stable fold is close to the point of thermodynamic equilibrium with the coil, all other forms of the chain being unstable close to the "all-or-none" transition midpoint. Here the analysis is the simplest: it must not take accumulating intermediates into account. True, the maximal folding ...
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... rapid pathway must include not too many steps, and, first of all, it must not require overcoming of a too high free energy barrier. An L-residue chain can attain its lowest-energy fold in L steps, each adding one fixed residue to the growing structure (Fig. 11). If the free energy went downhill along the entire pathway, a 100-residue chain would fold in ∼100-1000 ns, since the growth of a structure (e.g., an α-helix) by one residue (τ ) is known to take a few nanoseconds [33]. Protein folding takes much more than 1000 ns only because of the free energy barrier, since most of the folding time ...
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... us consider such a sequential (Fig. 11) protein folding: at each step of this process, one residue leaves the coil and takes its final position in the lowest-energy structure. This pathway looks a bit artificial, but it is exactly the pathway of unfolding of the lowest-energy structure, went in the opposite direction. The detailed balance law [90] reads that direct and ...
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... in the equilibrium point, the free energies of the native and the unfolded phases are equal, the additional free energy G # of the nucleus is due only to the boundary between the native and the unfolded phases. If the boundary goes across the globule (Fig. 11), it includes not more than ≈L 2/3 out of L residues of the ...
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... depending on the protein chain fold and the boundary position, the boundary may be or may be not covered by the unfolded closed loops (see the larger semi-folded structure in Fig. 11). The entropy lost by closed loops increases the conventional surface energy of the boundary. This entropy loss is between zero (if the boundary is not covered with loops) and −RL 2/3 (for the largest boundary corresponding to the globule's equator, when this boundary is densely covered with loops). Thus, the free energy caused by the ...
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... of them [77]. Since a characteristic time of rearrangement of one residue τ is ≈10 ns [33], it takes up to ∼10 ns × exp(1.5L 2/3 ) to overcome the free energy barrier of nucleation in the first case, and only ∼10 ns × exp(0.5L 2/3 ) in the second. This range is exactly consistent with the observed times of protein folding near the mid-transition (Fig. 12). It has been estimated that knotting of a 100-300-residue chain can increase this time insignificantly, a few times at most ...
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... of secondary importance when the folding takes place close to the mid-transition and G # is ∼L 2/3 RT , but it seems to be the most important effect when the native fold is much more stable than all its competitors and than the denatured state of the chain, and, correspondingly, when the folding nucleus size and free energy are smaller [93,94]. Fig. 12. Observed folding time at the point of equilibrium between the unfolded and the native states vs L 2/3 (L being the number of residues in the chain). The circles correspond to the α-helical (α) and β-hairpin (β) peptides [39,106] and to all 36 proteins listed in [60], whose folding time at the mid-transition can be calculated from the ...
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... as well. At first, this only increases the folding rate (see the rise of the left chevron limb from the mid-transition in Fig. 9), since the folding nucleus is stabilized, and the misfolded structures com- peting with the native fold are still unstable (relative to the initial unfolded state) due to the energy gap between them and the native fold (Fig. 13a). It has been estimated [77] that each additional 1 kcal/mol in stability of the native (relatively to unfolded) state decrease the barrier height by ≈ 1/2 kcal/mol (since the critical nucleus includes about a half of the protein), and the decreased instability of the nucleus correspondingly accelerates the ...
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... folding rate is achieved when the "misfolded" states become as stable as the unfolded state, i.e., when the folding intermediates arise (see the plateau at the top of the left chevron limb in Fig. 9b). The further increase in stability of the folded states leads to a rapid misfolding followed by a relatively slow conversion into the native state (Fig. 13b). Fig. 13. Folding under conditions when (a) the most stable fold N is only a little more stable than the unfolded chain U, and (b) when N is much more stable than U. The free energies of mis-or semi-folded structures are shown by numerous lines M (we should mention that it is not assumed that compactness of these structures is equal to ...
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... is achieved when the "misfolded" states become as stable as the unfolded state, i.e., when the folding intermediates arise (see the plateau at the top of the left chevron limb in Fig. 9b). The further increase in stability of the folded states leads to a rapid misfolding followed by a relatively slow conversion into the native state (Fig. 13b). Fig. 13. Folding under conditions when (a) the most stable fold N is only a little more stable than the unfolded chain U, and (b) when N is much more stable than U. The free energies of mis-or semi-folded structures are shown by numerous lines M (we should mention that it is not assumed that compactness of these structures is equal to that of ...
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... this chapter, it is worthwhile to consider a case when two (or more) protein structures instead of one are separated from others with a large energy gap. In this case the structure with the lower folding barrier is the first to fold, but, if it is less stable than another one, it will later undergo a slow (see Fig. 13) transition to this another structure. This transition is similar to the polymorphous transition in crystals (recall the "tin disease", i.e., transition of white tin into gray tin). The "polymorphous" proteins must be rare, since, if a sequence that makes a significant stabilization of one fold is a kind of wonder, then the sequence ...
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... nucleus", the folded part of transition state, plays a key role in protein folding: its instability determines the folding and unfolding rates. It should be stressed that the folding nucleus is not the molten Fig. 14. Folding nucleus identification using site-directed mutations (a scheme). (a) Mutation of residue, having its native environment and conformation (i.e., its native interactions) already in the transition state TS, changes the mutant's folding rate rather than its unfolding rate. (b) Mutation of residue, which remains denatured in the ...
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... (a) Mutation of residue, having its native environment and conformation (i.e., its native interactions) already in the transition state TS, changes the mutant's folding rate rather than its unfolding rate. (b) Mutation of residue, which remains denatured in the TS, has the opposite effect. "w.t" means "wild type", i.e., non-mutated protein. Fig. 15. Experimentally outlined folding nucleus for CheY protein [123]. The experimentally studied residues are shown as beads against the background of the native chain fold. The residues forming the folding nucleus are shown in black. Usually, the nucleus is shifted to the surface and does not coincide (though partially overlaps) with the ...
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... far, there is only one (unfortunately, only one and very laborious) experimental method to identify folding nuclei in proteins: to find residues whose mutations affect the folding rate by changing the TS stability as strongly as that of the native protein (Figs. 14, 15). For the basics of this method and pioneer works see ...
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... with different amino acid sequences but with similar three-dimensional structures have similar folding nuclei as a rule [127][128][129]. However, there are several examples which show that this is not always true (Fig. ...
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... a single conformation, and that it can be described by an order parameter, such as the fraction of native contacts. The TS search is based on the projection of the folding trajectories onto a single reaction coordinate (the fraction of the native contacts) and investigation of barriers at the obtained free- energy profiles (like those shown in Figs. 9, 13) [151][152][153]. Although such a projection is not a rigorous procedure (e.g., the structure which is "nearly native" in the terms of contacts, can contain an additional knot of the chain, and need complete unfolding before coming to the native state), these studies were able to outline, though crudely, the folding nuclei of some ...
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... nucleation gave a key to solve the Levinthal paradox and to estimate the characteristic protein folding rates (see Fig. 12). The correlation between folding rates and protein sizes is not as large, 60%. It has been shown, though, that the protein size by itself determines folding rates of only three-state folding proteins and fails to predict those for two-state folders ...

Citations

... In this work, we achieve this through the addition of the denaturant urea. Urea is known to destabilize folded proteins by lowering their thermodynamic stability 45,46 and increasing their unfolding rate 38,47,48 (decreasing kinetic stability) and in high concentration causes proteins to unfold completely. ...
Article
Globular folded proteins are versatile nanoscale building blocks to create biomaterials with mechanical robustness and inherent biological functionality due to their specific and well-defined folded structures. Modulating the nanoscale unfolding of protein building blocks during network formation (in situ protein unfolding) provides potent opportunities to control the protein network structure and mechanics. Here, we control protein unfolding during the formation of hydrogels constructed from chemically cross-linked maltose binding protein using ligand binding and the addition of cosolutes to modulate protein kinetic and thermodynamic stability. Bulk shear rheology characterizes the storage moduli of the bound and unbound protein hydrogels and reveals a correlation between network rigidity, characterized as an increase in the storage modulus, and protein thermodynamic stability. Furthermore, analysis of the network relaxation behavior identifies a crossover from an unfolding dominated regime to an entanglement dominated regime. Control of in situ protein unfolding and entanglement provides an important route to finely tune the architecture, mechanics, and dynamic relaxation of protein hydrogels. Such predictive control will be advantageous for future smart biomaterials for applications which require responsive and dynamic modulation of mechanical properties and biological function.
... Such systems generalize a polymer at the discontinuous pinning-depinning phase transition and have been identified and named critical in Ref. [16]. Critical renewal models are found in the theory of DNA and proteins since the DNA denaturation transition is generally believed to be discontinuous [21,22] and the protein folding process is regarded as an "all-or-none" transition [23], which is a microscopic analog of a discontinuous phase transition. Phase transitions are investigated by changing a control parameter, such as the temperature or the denaturant concentration, and the hallmark of discontinuous phase transitions is a discontinuity in the graph of the expected value of some extensive observable as a function of the control parameter. ...
Article
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We investigate the sharp asymptotic behavior at criticality of the large fluctuations of extensive observables in renewal models of statistical mechanics, such as the Poland-Scheraga model of DNA denaturation, the Fisher-Felderhof model of fluids, the Wako-Saitô-Muñoz-Eaton model of protein folding, and the Tokar-Dreyssé model of strained epitaxy. These models amount to Gibbs changes of measure of a classical renewal process and can be identified with a constrained pinning model of polymers. The extensive observables that enter the thermodynamic description turn out to be cumulative rewards corresponding to deterministic rewards that are uniquely determined by the waiting time and grow no faster than it. The probability decay with the system size of their fluctuations switches from exponential to subexponential at criticality, which is a regime corresponding to a discontinuous pinning-depinning phase transition. We describe such decay by proposing a precise large deviation principle under the assumption that the subexponential correction term to the waiting time distribution is regularly varying. This principle is in particular used to characterize the fluctuations of the number of renewals, which measures the DNA-bound monomers in the Poland-Scheraga model, the particles in the Fisher-Felderhof model and the Tokar-Dreyssé model, and the native peptide bonds in the Wako-Saitô-Muñoz-Eaton model.
... Such systems generalize a polymer at the discontinuous pinning-depinning phase transition and have been identified and named critical in Ref. [16]. Critical renewal models are found in the theory of DNA and proteins since the DNA denaturation transition is generally believed to be discontinuous [21,22] and the protein folding process is regarded as an "all-or-none" transition [23], which is a microscopic analog of a discontinuous phase transition. Phase transitions are investigated by changing a control parameter, such as the temperature or the denaturant concentration, and the hallmark of discontinuous phase transitions is a discontinuity in the graph of the expected value of some extensive observable as a function of the control parameter. ...
Preprint
Full-text available
We investigate the sharp asymptotic behavior at criticality of the large fluctuations of extensive observables in renewal models of statistical mechanics, such as the Poland-Scheraga model of DNA denaturation, the Fisher-Felderhof model of fluids, the Wako-Sait\^o-Mu\~noz-Eaton model of protein folding, and the Tokar-Dreyss\'e model of strained epitaxy. These models amount to Gibbs changes of measure of a classical renewal process and can be identified with a constrained pinning model of polymers. The extensive observables that enter the thermodynamic description turn out to be cumulative rewards corresponding to deterministic rewards that are uniquely determined by the waiting time and grow no faster than it. The probability decay with the system size of their fluctuations switches from exponential to subexponential at criticality, which is a regime corresponding to a discontinuous pinning-depinning phase transition. We describe such decay by proposing a precise large deviation principle under the assumption that the subexponential correction term to the waiting time distribution is regularly varying. This principle is in particular used to characterize the fluctuations of the number of renewals, which measures the DNA-bound monomers in the Poland-Scheraga model, the particles in the Fisher-Felderhof model and the Tokar-Dreyss\'e model, and the native peptide bonds in the Wako-Sait\^o-Mu\~noz-Eaton model.
... Protein folding has been an open challenge in science for many years (Finkelstein & Galzitskaya, 2004;Ołdziej et al., 2005;Rose et al., 2006;AlQuraishi, 2019a). The goal of protein folding is to predict the 3D structure of a peptide chain given its amino acids (residues) composition. ...
Preprint
Full-text available
Recent advancements in machine learning techniques for protein folding motivate better results in its inverse problem -- protein design. In this work we introduce a new graph mimetic neural network, MimNet, and show that it is possible to build a reversible architecture that solves the structure and design problems in tandem, allowing to improve protein design when the structure is better estimated. We use the ProteinNet data set and show that the state of the art results in protein design can be improved, given recent architectures for protein folding.
... The folding of the modern proteins is a very complex and highly specialized process (Finkelstein and Galzitskaya 2004) which complicated and evolved for many ages to adapt the final spatial structure of each distinct molecule to its functions. So, the analysis of the folding dynamics of modern proteins brings little data on its early development and origin. ...
Article
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The N-trifluoroacetylated α-aminoalcohols (TFAAAs) are able to form quasi-one-dimensional supramolecular fibers (strings) when chirally pure, and isometric precipitates in the racemate. The strings’ formation leads to the reversible gelation of the solution. The fresh gels occupy all the available volume, however during the incubation, they contract and concentrate in the central region of the tube. The microscopic observations revealed the growth of the strings’ diameter and their rotation in the course of the incubation at the hour time-scale. The rotation provides for the hairpins forming that serve as hooks on the rotating string, which provides for coiling of the strings, which was observed as gel contraction. The morphology of the twisted strings resembles the structures observed in modern proteins, which allows drawing an analogy between the folding of biopolymers and the formation of the clew of strings. In addition, the rotation found in the TFAAA gels is an example of a simple system converting the energy of intermolecular agglutination to the rotational movement, so they could be considered as molecular motors.
... Article "sampled" conformations on a (conformation-dependent) energetic profile while gradually progressing toward the folded state. 2,49,50 This model anticipates many local minima. The molten globule model presupposes that an important intermediate step is the existence of a partially folded structure with key secondary units already formed, 51 although not yet stabilized by native long-range interactions present in the tertiary structure of the native state. ...
Article
Full-text available
The analysis of folding trajectories for proteins is an open challenge. One of the problems is how to describe the amount of folded secondary structure in a protein. We extend the use of Estradas’ folding degree (Bioinformatics2002, 18, 697) for the analysis of the evolution of the folding stage during molecular dynamics (MD) simulation. It is shown that residue contribution to the total folding degree is a predominantly local property, well-defined by the backbone dihedral angles at the given residue, without significant contribution from the backbone conformation of other residues. Moreover, the magnitude of this residue contribution can be quite easily associated with characteristic motifs of secondary protein structures such as the α-helix, β-sheet (hairpin), and so on by means of a Ramachandran-like plot as a function of backbone dihedral angles φ,ψ. Additionally, the understanding of the free energy profile associated with the folding process becomes much simpler. Often a 1D profile is sufficient to locate global minima and the corresponding structure for short peptides.
... On the contrary, according to the direct mechanism, urea locally interacts with protein rather than impacting the water network resulting in changes in the global landscape of the protein. Protein is an amino acid heteropolymer with a unique (for each protein) sequence (Finkelstein and Galzitskaya 2004;Onuchic et al. 1997); its chemically complex construct is made of peptide backbone and side chains which can have polar, apolar, or charged variants. Scientists have spent decades to find whether side chain or backbone or even both have dominant contributions in urea-protein interactions as well as their nature of interaction. ...
Article
Noncovalent interactions are key determinants in both chemical and biological processes. Among such processes, the hydrophobic interactions play an eminent role in folding of proteins, nucleic acids, formation of membranes, protein-ligand recognition, etc.. Though this interaction is mediated through the aqueous solvent, the stability of the above biomolecules can be highly sensitive to any small external perturbations, such as temperature, pressure, pH, or even cosolvent additives, like, urea—a highly soluble small organic molecule utilized by various living organisms to regulate osmotic pressure. A plethora of detailed studies exist covering both experimental and theoretical regimes, to understand how urea modulates the stability of biological macromolecules. While experimentalists have been primarily focusing on the thermodynamic and kinetic aspects, theoretical modeling predominantly involves mechanistic information at the molecular level, calculating atomistic details applying the force field approach to the high level electronic details using the quantum mechanical methods. The review focuses mainly on examples with biological relevance, such as (1) urea-assisted protein unfolding, (2) urea-assisted RNA unfolding, (3) urea lesion interaction within damaged DNA, (4) urea conduction through membrane proteins, and (5) protein-ligand interactions those explicitly address the vitality of hydrophobic interactions involving exclusively the urea-aromatic moiety.
... Theories developed for the prediction of protein folding nuclei, experimentally studied by Alan Fersht [182] and others that one can find in [183][184][185][186][187][188][189][190][191][192][193], and a more detailed theoretical consideration of folding times for proteins of different sizes, chain folds, and stabilities, are given in [176,181,[194][195][196][197]. A limited-influence chain knotting and the SS-bonds in the single-domain proteins on the folding rate were estimated in [173,187], and the influence of the native structure stability on the folding rate was estimated in [176] (see also [198]). ...
Article
Full-text available
Proteins, these evolutionarily-edited biological polymers, are able to undergo intramolecular and intermolecular phase transitions. Spontaneous intramolecular phase transitions define the folding of globular proteins, whereas binding-induced, intra- and inter- molecular phase transitions play a crucial role in the functionality of many intrinsically-disordered proteins. On the other hand, intermolecular phase transitions are the behind-the-scenes players in a diverse set of macrosystemic phenomena taking place in protein solutions, such as new phase nucleation in bulk, on the interface, and on the impurities, protein crystallization, protein aggregation, the formation of amyloid fibrils, and intermolecular liquid–liquid or liquid–gel phase transitions associated with the biogenesis of membraneless organelles in the cells. This review is dedicated to the systematic analysis of the phase behavior of protein molecules and their ensembles, and provides a description of the major physical principles governing intramolecular and intermolecular phase transitions in protein solutions.
... Authors often emphasize the "physical nature" of their models for how proteins fold (e.g. [Finkelstein, Badretdinov 1997a] and treat it as a physics problem [Finkelstein, Galzitskaya 2004]. Nonetheless, some workers have reminded the field that there could be help for folding in achieving specific folds in the cell itself, including by the structure of codons [Saunders and Deane,2007] . ...
... During W/O/W production of microparticles, the protein therapeutic is exposed to an aqueous/organic interface during emulsification with the polymer. Proteins in aqueous solution are folded to minimize hydrophobic interactions with the surrounding water, and the resulting active conformation of proteins typically has a hydrophobic core (Dill, 1990;Finkelstein & Galzitskaya, 2004). Exposure to the aqueous/organic interface induces protein unfolding, adsorption, and aggregation (Norde & Favier, 1992;Zhai et al., 2010;. ...
Article
Injectable or implantable poly(lactic‐co‐glycolic acid) (PLGA) devices for the sustained delivery of proteins have been widely studied and utilized to overcome the necessity of repeated administrations for therapeutic proteins due to poor pharmacokinetic profiles of macromolecular therapies. These devices can come in the form of microparticles, implants, or patches depending on the disease state and route of administration. Furthermore, the release rate can be tuned from weeks to months by controlling the polymer composition, geometry of the device, or introducing additives during device fabrication. Slow‐release devices have become a very powerful tool for modern medicine. Production of these devices has initially focused on emulsion‐based methods, relying on phase separation to encapsulate proteins within polymeric microparticles. Process parameters and the effect of additives have been thoroughly researched to ensure protein stability during device manufacturing and to control the release profile. Continuous fluidic production methods have also been utilized to create protein‐laden PLGA devices through spray drying and electrospray production. Thermal processing of PLGA with solid proteins is an emerging production method that allows for continuous, high‐throughput manufacturing of PLGA/protein devices. Overall, polymeric materials for protein delivery remain an emerging field of research for the creation of single administration treatments for a wide variety of disease. This review describes, in detail, methods to make PLGA devices, comparing traditional emulsion‐based methods to emerging methods to fabricate protein‐laden devices. This article is categorized under: • Biology‐Inspired Nanomaterials > Protein and Virus‐Based Structures • Implantable Materials and Surgical Technologies > Nanomaterials and Implants • Biology‐Inspired Nanomaterials > Peptide‐Based Structures