Effect of polyethylene glycols on the alkaline-induced molten globule intermediate of bovine serum albumin

ArticleinInternational journal of biological macromolecules 51(1-2):97-104 · April 2012with12 Reads
DOI: 10.1016/j.ijbiomac.2012.04.021 · Source: PubMed
In the present study, the formation of one molten globule-like unfolding intermediate of bovine serum albumin (BSA) at pH 11.2 has been established with the help of circular dichroism (CD) spectra, fluorescence spectroscopy and 'phase diagram' approach. Additionally, we have shown the conformational changes occurring in the pH 11.2 intermediate of BSA when it was exposed to different molecular weight polyethylene glycols (PEGs) at varying concentrations. When the pH 11.2 intermediate of BSA was treated by PEG 400 there was induction of secondary and non-native tertiary contacts. In case of PEG 8000 and PEG 20,000, the loss in secondary as well as tertiary structure was observed. PEG 8000 and 20,000 altered the conformation of the pH 11.2 intermediate and resulted in its transition to another intermediate state in which the hydrophobic patches were inaccessible.
    • "This implies that a greater extent of PEG-protein interactions results in a further removal of ANS from the hydrophobic region of proteins resulting in attenuation in the ANS fluorescence. It has been observed earlier that PEG of different molecular weight (400, 8000, 20,000) causes attenuation in the ANS fluorescence intensity and this reduction becomes significant at higher concentration of PEGs [60] which we found to be true in our case also. "
    [Show abstract] [Hide abstract] ABSTRACT: Molten globule state plays a crucial role in the amyloidogenesis of several proteins. Hen egg white lysozyme (HEWL) acquires a molten globule state at alkaline pH (12.75). Our study reveals a significant inhibitory effect of high molecular weight polyethylene glycols (PEG) (PEG 20000 and PEG 35000) against alkali-salt mediated fibrillation of HEWL. Native state of HEWL is stabilized in the presence of PEGs accompanied by a decrease in the β-sheet content. Enzymatic activity of HEWL is mostly retained in the presence of polyethylene glycols. The comparable hydrodynamic radius (Rh) of PEG 20000 and native HEWL is central reason to the greater inhibitory potency of PEG 20000 against HEWL fibrillation.
    Full-text · Article · Sep 2014
    • "ANS fluorescence is further used to detect and quantify the exposed hydrophobic patches on proteins upon interacting with polymers. Since ANS dye displays enhanced fluorescence and a characteristic blue shift in its fluorescence emission maximum from 515 to 475 nm when bound to protein hydrophobic surfaces [52,53], ANS fluorescence is especially useful in detecting partially folded conformations of globular proteins.Fig. 4 shows an ANS fluorescence signal of BSA upon interacting with pSBMA or PEG at different time points. In the presence of pSBMA (Fig. 4A), ANS fluorescence of pSBMA–BSA mixtures with different ratios was similar to each other and to that of pure BSA at different time points (0, 5 and 24 h). "
    [Show abstract] [Hide abstract] ABSTRACT: Protein-polymer interactions are of great interest in a wide range of scientific and technological applications. Neutral poly(ethylene glycol) (PEG) and zwitterionic poly(sulfobetaine methacrylate)(pSBMA) are two well-known nonfouling materials that exhibit strong surface resistance to proteins. However, it still remains unclear or unexplored how PEG and pSBMA interact with proteins in solution. In this work, we examine the interactions between two model proteins (bovine serum albumin and lysozyme) and two typical antifouling polymers of PEG and pSBMA in the aqueous solution using fluorescence spectroscopy, atomic force microscopy, and NMR. The effect of mass ratios of protein:polymer on the interactions is also examined. Collective data clearly demonstrate the existence of weak hydrophobic interactions between PEG and proteins, while no detectable interactions between pSBMA and proteins. The elimination of protein interaction with pSBMA could be due to an enhanced surface hydration of zwitterionic groups in pSBMA. New evidence is given to demonstrate the interactions between PEG and proteins, which are often neglected in literature because the PEG-protein interactions are weak and reversible, as well as the structural change caused by hydrophobic interaction. This work provides a better fundamental understanding of the intrinsic structure-activity relationship of polymers underlying polymer-protein interactions, which are important for designing new biomaterials for biosensor, medical diagnostics, and drug delivery applications.
    Full-text · Article · Oct 2013
  • [Show abstract] [Hide abstract] ABSTRACT: Polymer–protein interactions are crucial for determining the activity of both polymer and protein for many bio-related applications. Poly(ethylene glycol) (PEG) as a well-known antifouling material is often coated on surfaces to form highly solvated brushes, which exhibit excellent protein-repellent properties. However, unlike surface-induced antifouling effects, little is known about the intrinsic PEG–protein interactions in aqueous solution, which is an important yet neglected problem. Here, we investigate the interactions between PEG and proteins in aqueous solution using fluorescence spectroscopy, atomic force microscopy (AFM), and nuclear magnetic resonance (NMR). Two important characteristics, molecular weight of PEG and mass ratio of PEG:protein, are examined to determine the effect of each on PEG–protein interactions as well as binding characteristics between PEG and proteins. In contrast to too long and too short PEG chains, collective results have shown that PEG with optimal molecular weight (MW) is more capable of interacting with proteins, which induces the conformational change of proteins through more stable binding sites and stronger interactions with long chain PEG. Enhanced PEG–protein interactions are likely due to the change of hydrophilicity to amphiphilicity of PEG with increasing MWPEG. In contrast to almost none or weak interactions of PEG surfaces with proteins, this work provides new evidence to demonstrate the existence of interactions between PEG and proteins in aqueous solution, which is important not only for better understanding of the structure–activity relationship of PEG both in solution and on surfaces, but also for the rational design of new PEG-based materials for specific applications.
    Full-text · Article · Apr 2014