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Michael S Kay

Publications and source records attributed to Michael S Kay.

4 recordsLinked to original sources
PubMed2006

A stiffness switch in human immunodeficiency virus.

After budding from the cell, human immunodeficiency virus (HIV) and other retrovirus particles undergo a maturation process that is required for their infectivity. During maturation, HIV particles undergo a significant internal morphological reorganization, changing from a roughly spherically symmetric immature particle with a thick protein shell to a mature particle with a thin protein shell and conical core. However, the physical principles underlying viral particle production, maturation, and entry into cells remain poorly understood. Here, using nanoindentation experiments conducted by an atomic force microscope (AFM), we report the mechanical measurements of HIV particles. We find that immature particles are more than 14-fold stiffer than mature particles and that this large difference is primarily mediated by the HIV envelope cytoplasmic tail domain. Finite element simulation shows that for immature virions the average Young's modulus drops more than eightfold when the cytoplasmic tail domain is deleted (930 vs. 115 MPa). We also find a striking correlation between the softening of viruses during maturation and their ability to enter cells, providing the first evidence, to our knowledge, for a prominent role for virus mechanical properties in the infection process. These results show that HIV regulates its mechanical properties at different stages of its life cycle (i.e., stiff during viral budding versus soft during entry) and that this regulation may be important for efficient infectivity. Our report of this maturation-induced "stiffness switch" in HIV establishes the groundwork for mechanistic studies of how retroviral particles can regulate their mechanical properties to affect biological function.

Biomechanical Phenomena↗
PubMed2005

Inhibiting HIV fusion with a beta-peptide foldamer.

Linear peptides derived from the HIV gp41 C-terminus (C-peptides), such as the 36-residue Fuzeon, are potent HIV fusion inhibitors. These molecules bind to the N-peptide region of gp41 and inhibit an intramolecular protein-protein interaction that powers fusion of the viral and host cell membranes. The N-peptide region contains a surface pocket that is occupied in the post-fusion state by three alpha-helical residues found near the gp41 C-terminus: Trp628, Trp631, and Ile635-the WWI epitope. Here, we describe a set of beta3-decapeptides (betaWWI-1-4) in which the WWI epitope is presented on one face of a short 14-helix stabilized by macrodipole neutralization and side chain-side chain salt bridges. betaWWI-1-4 bind in vitro to IZN17, a validated gp41 model, and inhibit syncytia formation in cell culture. Molecules lacking a complete WWI functional epitope neither bind IZN17 nor inhibit syncytia formation. These results provide evidence that short beta-peptide 14-helices can inhibit an intramolecular protein-protein interaction in vivo. Molecules related to betaWWI-1-4 could represent starting points for the development of highly potent inhibitors or antigens effective against HIV or other viruses, including SARS, Ebola, HRSV, and influenza, that employ common fusion mechanisms.

Cell Fusion↗
PubMed2005

Steric accessibility of the HIV-1 gp41 N-trimer region.

During human immunodeficiency virus entry, gp41 undergoes a series of conformational changes that induce membrane fusion. Immediately prior to fusion, gp41 exists in a prehairpin intermediate in which the N- and C-peptide regions of gp41 are exposed. Rearrangement of this intermediate into a six-helix bundle composed of a trimeric coiled coil from the N-peptide region (N-trimer) surrounded by three peptides from the C-peptide region provides the driving force for membrane fusion, whereas prevention of six-helix bundle formation inhibits viral entry. Because of its central role in mediating viral entry, the N-trimer region of gp41 is a key vaccine target. Extensive efforts to discover potent and broadly neutralizing antibodies (Abs) against the N-trimer region have, thus far, been unsuccessful. In this study, we attached a potent C-peptide inhibitor that binds to the N-trimer region to cargo proteins of various sizes to examine the steric accessibility of the N-trimer during fusion. These inhibitors show a progressive loss of potency with increasing cargo size. Extension of the cargo/C-peptide linker partially restores inhibitory potency. These results demonstrate that the human immunodeficiency virus defends its critical hairpin-forming machinery by steric exclusion of large proteins and may explain the current dearth of neutralizing Abs against the N-trimer. In contrast, previous results suggest the C-peptide region is freely accessible during fusion, demonstrating that the N- and C-peptide regions are in structurally distinct environments. Based on these results, we also propose new strategies for the generation of neutralizing Abs that overcome this steric block.

Antibodies, Monoclonal↗