[Show abstract][Hide abstract] ABSTRACT: To extend the potency of vaccines against infectious diseases, vaccines should be able to exploit multiple arms of the immune system. One component of the immune system that is under-used in vaccine design is the subset of B cells known to be capable of responding to repetitive antigenic epitopes and differentiate into plasma cells even in the absence of T cell help (T-independent, TI).
To target vaccine responses from T-independent B cells, we reengineered a bacterial Flagellin (FliC) by replacing its exposed D3 domain with a viral envelope protein from Dengue virus (DENV2). The resulting hybrid FliC protein (hFliC) was able to form stable filaments decorated with conformationally intact DENV2 envelope domains. These filaments were not only capable of inducing a T cell-dependent (TD) humoral antibody response, but also significant IgM and IgG3 antibody response in a helper T cell repertoire-restricted transgenic mouse model.
Our results provide proof-of-principle demonstration that a reengineered hybrid FliC could be used as a platform for polymeric subunit vaccines, enhancing T cell-dependent and possibly inducing T-independent antibody responses from B-1 B cells as well.
[Show abstract][Hide abstract] ABSTRACT: Complement activation plays a major role in many acute and chronic inflammatory conditions. C3d, a terminal product of complement activation, remains covalently attached to cells, and is an excellent biomarker of complement-mediated inflammation. We employed a virtual high-throughput screening protocol to identify molecules with predicted binding to complement C3d and with intrinsic fluorescence properties to enable detection. Pharmacophore models were developed based on known C3d-ligand interactions and information from computational analysis of structural and molecular dynamics data. Iterative pharmacophore-based virtual screening was performed to identify drug-like molecules with physicochemical similarity to the natural C3d ligand CR2. Hits from the pharmacophore screens were docked to C3d and ranked based on predicted binding free energies. Top-ranked molecules were selected for experimental validation of binding affinity to C3d, using microscale thermophoresis, and for their suitability to become molecular imaging agents, using fluorescence spectroscopy. This work serves as a foundation for identifying additional fluorescent molecules with high-affinity for C3d that will subsequently be explored as noninvasive in vivo diagnostics of complement-mediated inflammation, spatiotemporal monitoring of disease progression, and for targeting therapeutics to sites of inflammation.
Journal of Medicinal Chemistry 11/2015; DOI:10.1021/acs.jmedchem.5b01062 · 5.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Adenoviruses bind to a variety of human cells to cause infection. Both the B2 adenovirus 11 and B1 adenovirus 21 use protein knobs to bind to complement regulator CD46(SCR1-2) in order to gain entry into host cells. In each complex, the two proteins are highly negatively charged but bind to each other at an interface with oppositely charged surface patches. We computationally generated single-alanine mutants of charged residues in the complexes CD46(SCR1-2)-Ad11k and CD46(SCR1-2)-Ad21k. We used electrostatic clustering and Poisson-Boltzmann free energy calculations to propose a hypothesis on the role of electrostatics in association. Our results delineate specific interfacial electrostatic interactions that are critical for association in both CD46(SCR1-2)-Ad11k and CD46(SCR1-2)-Ad21k. These results will serve as a predictive tool in the selection of mutants with desired binding affinity in experimental mutagenesis studies. This study will also serve as a foundation for the design of inhibitors to treat adenovirus infections.
[Show abstract][Hide abstract] ABSTRACT: As a part of innate immunity, the complement system relies on activation of the alternative pathway (AP). While feed-forward amplification generates an immune response towards foreign surfaces, the process requires regulation to prevent an immune response on the surface of host cells. Factor H (FH) is a complement protein secreted by native cells to negatively regulate the AP. In terms of structure, FH is composed of 20 complement-control protein (CCP) modules that are structurally homologous but vary in composition and function. Mutations in these CCPs have been linked to states of autoimmunity. In particular, several mutations in CCP 19-20 are correlated to atypical hemolytic uremic syndrome (aHUS). From crystallographic structures there are three putative binding sites of CCP 19-20 on C3d. Since there has been some controversy over the primary mode of binding from experimental studies, we approach characterization of binding using computational methods. Specifically, we compare each binding mode in terms of electrostatic character, structural stability, dissociative and associative properties, and predicted free energy of binding. After a detailed investigation, we found two of the three binding sites to be similarly stable while varying in the number of contacts to C3d and in the energetic barrier to complex dissociation. These sites are likely physiologically relevant and may facilitate multivalent binding of FH CCP 19-20 to C3b and either C3d or host glycosaminoglycans. We propose thermodynamically stable binding with modules 19 and 20, the latter driven by electrostatics, acting synergistically to increase the apparent affinity of FH for host surfaces. This article is protected by copyright. All rights reserved.
Protein Science 01/2015; 24(5). DOI:10.1002/pro.2650 · 2.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Compstatin peptides are complement inhibitors that bind and inhibit cleavage of complement C3. Peptide binding is enhanced by hydrophobic interactions, however poor solubility promotes aggregation in aqueous environments. We have designed new compstatin peptides derived from the W4A9 sequence (Ac-ICVWQDWGAHRCT-NH2, cyclized between C2 and C12), based on structural, computational, and experimental studies. Furthermore, we developed and utilized a computational framework for the design of peptides containing non- natural amino acids. These new compstatin peptides contain polar N-terminal extensions and non-natural amino acid substitutions at positions 4 and 9. Peptides with alpha-modified non- natural alanine analogs at position 9, as well as peptides containing only N-terminal polar extensions, exhibited similar activity compared to W4A9, as quantified via ELISA, hemolytic, and cell-based assays, and showed improved solubility, as measured by UV absorbance and reverse-phase HPLC experiments. Due to their potency and solubility, these peptides are promising candidates for therapeutic development in numerous complement-mediated diseases.
[Show abstract][Hide abstract] ABSTRACT: The complement cascade is a highly sophisticated network of proteins that are well regulated and directed in response to invading pathogens or tissue injury. Complement C3a and C5a are key mediators produced by this cascade, and their dysregulation has been linked to a plethora of inflammatory and autoimmune diseases. Consequently, this has stimulated interest in the development of ligands for the receptors for these complement peptides, C3a receptor, and C5a1 (C5aR/CD88). In this study we used computational methods to design novel C5a1 receptor ligands. However, functional screening in human monocyte-derived macrophages using the xCELLigence label-free platform demonstrated altered specificity of our ligands. No agonist/antagonist activity was observed at C5a1, but we instead saw that the ligands were able to partially agonize the closely related complement receptor C3a receptor. This was verified in the presence of C3a receptor antagonist SB 290157 and in a stable cell line expressing either C5a1 or C3a receptor alone. C3a agonism has been suggested to be a potential treatment of acute neutrophil-driven traumatic pathologies, and may have great potential as a therapeutic avenue in this arena.
European Journal of Pharmacology 10/2014; 745. DOI:10.1016/j.ejphar.2014.10.041 · 2.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The complement system surveillance in the host is effective in controlling viral propagation. Consequently, to subvert this effector mechanism, viruses have developed a series of adaptations. One among these is encoding mimics of host regulators of complement activation (RCA) which help viruses to avoid being labeled as ‘foreign’ and protect them from complement-mediated neutralization and complement-enhanced antiviral adaptive immunity. In this review, we provide an overview on the structure, function and evolution of viral RCA proteins.
[Show abstract][Hide abstract] ABSTRACT: Background
The complement protein C5a acts by primarily binding and activating the G-protein coupled C5a receptor C5aR (CD88), and is implicated in many inflammatory diseases. The cyclic hexapeptide PMX53 (sequence Ace-Phe-[Orn-Pro-dCha-Trp-Arg]) is a full C5aR antagonist of nanomolar potency, and is widely used to study C5aR function in disease.
We construct for the first time molecular models for the C5aR:PMX53 complex without the a priori use of experimental constraints, via a computational framework of molecular dynamics (MD) simulations, docking, conformational clustering and free energy filtering. The models agree with experimental data, and are used to propose important intermolecular interactions contributing to binding, and to develop a hypothesis for the mechanism of PMX53 antagonism.
This work forms the basis for the design of improved C5aR antagonists, as well as for atomic-detail mechanistic studies of complement activation and function. Our computational framework can be widely used to develop GPCR-ligand structural models in membrane environments, peptidomimetics and other chemical compounds with potential clinical use.
[Show abstract][Hide abstract] ABSTRACT: The complement system surveillance in the host is effective in controlling viral propagation. Consequently, to subvert this effector mechanism, viruses have developed a series of adaptations. One among these is encoding mimics of host regulators of complement activation (RCA) which help viruses to avoid being labeled as 'foreign' and protect them from complement-mediated neutralization and complement-enhanced antiviral adaptive immunity. In this review, we provide an overview on the structure, function and evolution of viral RCA proteins.
[Show abstract][Hide abstract] ABSTRACT: SAME SAME Cell and Molecular Biology section/symposium Oral/poster presentation Student The role of AlgX carbohydrate-binding module during alginate biosynthesis in Pseudomonas aeruginosa, Cystic fibrosis is a chronic, progressive, and often fatal genetic inherited disease caused by mutations in the gene that encodes the cystic fibrosis transmembrane conductance regulator (CFTR). Alginate or mucoid encapsulated Pseudomonas aeruginosa is the causative agent of respiratory insufficiency and failure in patients with cystic fibrosis. We have previously reported that AlgX is a protein required for alginate biosynthesis. Recently, AlgX has been reported to play a role in the modification of alginate through acetylation. In this study, we show that the absence of AlgX resulted in the loss of mucoidy due to the degradation of nascent alginate by the alginate lyase, AlgL. Using computational molecular docking studies and alginate affinity assay, we show that AlgX binds alginate via the carbohydrate-binding module located in the C-terminal region. Alanine mutations of the predicted amino acid residues that interact with alginate suggest that K338, R370, T372, and R380 are important for alginate binding. Alginate rescue assay by in trans expression of mutant AlgX in a chromosomal algX deleted P. aeruginosa mutant confirms the importance of these amino acid residues during alginate biosynthesis. In summary, these studies suggest that AlgX protects the alginate polymers from AlgL degradation, binds alginate via the carbohydrate-binding module, and is conceivably located in the biosynthetic scaffold serving as an appendage to the alginate acetylation machinery. In conclusion, AlgX binds alginate via the carbohydrate-binding module and is required for alginate biosynthesis and modification. Abstract contains 236/250 words
American Association for the Advancement of Science, Riverside, CA; 06/2014
[Show abstract][Hide abstract] ABSTRACT: Staphylococcus aureus expresses numerous virulence factors that aid in immune evasion. The four-domain staphylococcal immunoglobulin binding (Sbi) protein interacts with complement component 3 (C3) and its thioester domain (C3d)-containing fragments. Recent structural data suggested two possible modes of binding of Sbi domain IV (Sbi-IV) to C3d, but the physiological binding mode remains unclear. We used a computational approach to provide insight into the C3d-Sbi-IV interaction. Molecular dynamics (MD) simulations showed that the first binding mode (PDB code 2WY8) is more robust than the second (PDB code 2WY7), with more persistent polar and nonpolar interactions, as well as conserved interfacial solvent accessible surface area. Brownian dynamics and steered MD simulations revealed that the first binding mode has faster association kinetics and maintains more stable intermolecular interactions compared to the second binding mode. In light of available experimental and structural data, our data confirm that the first binding mode represents Sbi-IV interaction with C3d (and C3) in a physiological context. Although the second binding mode is inherently less stable, we suggest a possible physiological role. Both binding sites may serve as a template for structure-based design of novel complement therapeutics.
[Show abstract][Hide abstract] ABSTRACT: We have used a novel human retinal pigmented epithelial (RPE) cell-based model that mimics drusen biogenesis and the pathobiology of age-related macular degeneration to evaluate the efficacy of newly designed peptide inhibitors of the complement system. The peptides belong to the compstatin family and, compared to existing compstatin analogs, have been optimized to promote binding to their target, complement protein C3, and to enhance solubility by improving their polarity/hydrophobicity ratios. Based on analysis of molecular dynamics simulation data of peptide-C3 complexes, novel binding features were designed by introducing intermolecular salt bridge-forming arginines at the N-terminus and at position -1 of N-terminal dipeptide extensions. Our study demonstrates that the RPE cell assay has discriminatory capability for measuring the efficacy and potency of inhibitory peptides in a macular disease environment.
Experimental Eye Research 08/2013; 116. DOI:10.1016/j.exer.2013.07.023 · 2.71 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Despite its sequence variability and structural flexibility, the V3 loop of the HIV-1 envelope glycoprotein gp120 is capable of recognizing cell-bound co-receptors CCR5 and CXCR4 and infecting cells. Viral selection of CCR5 is associated with the early stages of infection, and transition to selection of CXCR4 indicates disease progression. We have developed a predictive statistical model for co-receptor selectivity that uses the discrete property of net charge and the binary co-receptor preference markers of the N6X7[T/S]8X9 glycosylation motif and 11/24/25 positive amino acid rule. The model is based on analysis of 2,054 V3 loop sequences from patient data and allows us to infer the most likely state of the disease from physicochemical characteristics of the sequences. The performance of the model is comparable to established sequence-based predictive methods, and may be used in combination with other methods as a supportive diagnostic for co-receptor selection. This model may be used for personalized medical decisions in administering co-receptor-specific therapies.
AIDS research and human retroviruses 06/2013; 29(10). DOI:10.1089/AID.2012.0173 · 2.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The interaction between complement fragment C3d and complement receptor 2 (CR2) is a key aspect of complement immune system activation, and is a component in a link between innate and adaptive immunities. The complement immune system is an ancient mechanism for defense, and can be found in species that have been on Earth for the last 600 million years. However, the link between the complement system and adaptive immunity, which is formed through the association of the B-cell co-receptor complex, including the C3d-CR2 interaction, is a much more recent adaptation. Human C3d and CR2 have net charges of -1 and +7 respectively, and are believed to have evolved favoring the role of electrostatics in their functions. To investigate the role of electrostatics in the function and evolution of human C3d and CR2, we have applied electrostatic similarity methods to identify regions of evolutionarily conserved electrostatic potential based on 24 homologues of complement C3d and 4 homologues of CR2. We also examine the effects of structural perturbation, as introduced through molecular dynamics and mutations, on spatial distributions of electrostatic potential to identify perturbation resistant regions, generated by so-called electrostatic "hot-spots". Distributions of electrostatic similarity based on families of perturbed structures illustrate the presence of electrostatic "hot-spots" at the two functional sites of C3d, while the surface of CR2 lacks electrostatic "hot-spots" despite its excessively positive nature. We propose that the electrostatic "hot-spots" of C3d have evolved to optimize its dual-functionality (covalently attaching to pathogen surfaces and interaction with CR2), which are both necessary for the formation B-cell co-receptor complexes. Comparison of the perturbation resistance of the electrostatic character of the homologues of C3d suggests that there was an emergence of a new role of electrostatics, and a transition in the function of C3d, after the divergence of jawless fish.
[Show abstract][Hide abstract] ABSTRACT: The V3 loop of the glycoprotein 120 (gp120) is a contact point for cell entry of HIV-1 leading to infection. Despite sequence variability and lack of specific structure, the highly flexible V3 loop possesses a well-defined role in recognizing and selecting cell-bound coreceptors CCR5 and CXCR4 through a mechanism of charge complementarity. We have performed two independent molecular dynamics (MD) simulations to gain insights into the dynamic character of two V3 loops with slightly different sequences, but significantly different starting crystallographic structures. We have identified highly populated trajectory-specific salt bridges between oppositely charged stem residues Arg9 and Glu25 or Asp29. The two trajectories share nearly identical correlated motions within the simulations, despite their different overall structures. High occupancy salt bridges play a key role in the major cross-correlated motions in both trajectories, and may be responsible for transient structural stability in preparation for coreceptor binding. In addition, the two V3 loops visit conformations with similarities in spatial distributions of electrostatic potentials, despite their inherent flexibility, which may play a role in coreceptor recognition. It is plausible that cooperativity between overall electrostatic potential, charged residue interactions, and correlated motions could be associated with a coreceptor selection and binding.
PLoS ONE 11/2012; 7(11):e49925. DOI:10.1371/journal.pone.0049925 · 3.23 Impact Factor