Role of Disulphide Bonds in Membrane Partitioning of a Viral Peptide

Role of Lipid Packing Defects in Determining Membrane Interactions of Antimicrobial Polymers

Understanding the emergence and role of lipid packing defects in the detection and subsequent partitioning of antimicrobial agents into bacterial membranes is essential for gaining insights into general antimicrobial mechanisms. Herein, using methacrylate polymers as a model platform, we investigate the effects of inclusion of various functional groups in the biomimetic antimicrobial polymer design on the aspects of lipid packing defects in model bacterial membranes. Two antimicrobial polymers are considered: ternary polymers composed of cationic, hydrophobic, and polar moieties and binary polymers with only cationic and hydrophobic moieties. We find that differing modes of insertion of these two polymers lead to different packing defects in the bacterial membrane. While insertion of both binary and ternary polymers leads to an enhanced number of deep defects in the upper leaflet, shallow defects are moderately enhanced upon interaction with ternary polymers only. We provide conclusive evidence that insertion of antimicrobial polymers in bacterial membrane is preceded by sensing of interfacial lipid packing defects. Our simulation results show that the hydrophobic groups are inserted at a single colocalized deep defect site for both binary and ternary polymers. However, the presence of polar groups in the ternary polymers use the shallow defects close to the lipid-water interface, in addition, to insert into the membrane, which leads to a more folded conformation of the ternary polymer in the membrane environment, and hence a different membrane partitioning mechanism compared to the binary polymer, which acquires an amphiphilic conformation.

Effect of Disulfide Bridge on the Binding of SARS-CoV-2 Fusion Peptide to Cell Membrane: A Coarse-Grained Study

In this paper, we present the parameterization of the CAVS coarse-grained (CG) force field for 20 amino acids, and our CG simulations show that the CAVS force field could accurately predict the amino acid tendency of the secondary structure. Then, we used the CAVS force field to investigate the binding of a severe acute respiratory syndrome-associated coronavirus fusion peptide (SARS-CoV-2 FP) to a phospholipid bilayer: a long FP (FP-L) containing 40 amino acids and a short FP (FP-S) containing 26 amino acids. Our CAVS CG simulations displayed that the binding affinity of the FP-L to the bilayer is higher than that of the FP-S. We found that the FP-L interacted more strongly with membrane cholesterol than the FP-S, which should be attributed to the stable helical structure of the FP-L at the C-terminus. In addition, we discovered that the FP-S had one major and two minor membrane-bound states, in agreement with previous all-atom molecular dynamics (MD) studies. However, we found that both the C-terminal and N-terminal amino acid residues of the FP-L can strongly interact with the bilayer membrane. Furthermore, we found that the disulfide bond formed between Cys840 and Cys851 stabilized the helices of the FP-L at the C-terminus, enhancing the interaction between the FP-L and the bilayer membrane. Our work indicates that the stable helical structure is crucial for binding the SARS-CoV-2 FP to cell membranes. In particular, the helical stability of FP should have a significant influence on the FP-membrane binding.

Thiol Modifications in the Extracellular Space—Key Proteins in Inflammation and Viral Infection

Posttranslational modifications (PTMs) allow to control molecular and cellular functions in response to specific signals and changes in the microenvironment of cells. They regulate structure, localization, stability, and function of proteins in a spatial and temporal manner. Among them, specific thiol modifications of cysteine (Cys) residues facilitate rapid signal transduction. In fact, Cys is unique because it contains the highly reactive thiol group that can undergo different reversible and irreversible modifications. Upon inflammation and changes in the cellular microenvironment, many extracellular soluble and membrane proteins undergo thiol modifications, particularly dithiol–disulfide exchange, S-glutathionylation, and S-nitrosylation. Among others, these thiol switches are essential for inflammatory signaling, regulation of gene expression, cytokine release, immunoglobulin function and isoform variation, and antigen presentation. Interestingly, also the redox state of bacterial and viral proteins depends on host cell-mediated redox reactions that are critical for invasion and infection. Here, we highlight mechanistic thiol switches in inflammatory pathways and infections including cholera, diphtheria, hepatitis, human immunodeficiency virus (HIV), influenza, and coronavirus disease 2019 (COVID-19).