Potent Peptides Inhibit HIV Entry Into Cells
Based in part on protein structures determined at the National Synchrotron Light Source (NSLS) at the U.S. Department of Energy’s Brookhaven National Laboratory, scientists at the University of Utah have developed new peptides that appear to be significantly more effective at blocking HIV’s entry into cells than other drugs in their class.
Structure of D-peptide inhibitors (green, yellow, and purple) bound to an HIV protein mimic in three “pockets” that are essential to the virus’ ability to enter cells. Blocking the pockets thwarts entry and reduces infectivity. (Credit: Image courtesy of DOE/Brookhaven National Laboratory)
In a paper being published online by the Proceedings of the National Academy of Sciences the week of October 8, 2007, the researchers say these peptides are sufficiently potent to begin pre-clinical studies as a new class of agents for the prevention and treatment of HIV/AIDS.
“Our ‘D-peptides’ offer several potential therapeutic advantages over existing peptide entry inhibitors, which are costly, require high dose injections, and suffer from the emergence of drug-resistance,” said University of Utah biochemist Michael S. Kay, lead author on the paper. “In contrast, our D-peptides resist degradation, so they have the potential to be administered by mouth and last longer in the bloodstream. Since these inhibitors have a unique inhibitory mechanism, they should work well in combination with existing HIV inhibitors.”
The researchers were particularly interested in developing drugs to bind to an essential “pocket” structure found in all HIV strains that was previously identified as a promising drug target using structures determined at Brookhaven’s NSLS. Numerous previous attempts to target this pocket failed to produce potent and non-toxic pocket-specific entry inhibitors. In the current work, the researchers used a high-throughput technique to screen a “library” containing hundreds of millions of peptides to identify the rare peptides that would bind to the pocket structure and inhibit HIV entry.
After identifying the most promising candidate peptides, the researchers analyzed the structure of these peptides bound to the target protein using x-ray crystallography at the NSLS. In this technique, researchers analyze how an extremely bright beam of x-rays, available only at synchrotron sources, bounces off and is refracted by the sample to determine the positions of individual atoms. “These structures reveal details of how the peptides bind and guide the development of future inhibitors,” said paper co-author Annie Heroux, a biologist and crystallography specialist at Brookhaven Lab.
This structure-assisted design led to the discovery of D-peptides with up to a 40,000-fold improved antiviral potency over previously reported D-peptides. The structures also suggest ways to engineer the peptides to reduce the chance of drug resistance.
PNAS | October 11, 2005 | vol. 102 | no. 41 | 14759-14764
A human monoclonal antibody neutralizes diverse HIV-1 isolates by binding a critical gp41 epitope
Michael D. Miller, Romas Geleziunas, Elisabetta Bianchi, Simon Lennard, Renee Hrin, Hangchun Zhang, Meiqing Lu, Zhiqiang An, Paolo Ingallinella, Marco Finotto, Marco Mattu, Adam C. Finnefrock, David Bramhill, James Cook, Debra M. Eckert, Richard Hampton, Mayuri Patel, Stephen Jarantow, Joseph Joyce, Gennaro Ciliberto, Riccardo Cortese, Ping Lu, William Strohl, William Schleif, Michael McElhaugh, Steven Lane, Christopher Lloyd, David Lowe, Jane Osbourn, Tristan Vaughan, Emilio Emini, Gaetano Barbato, Peter S. Kim, Daria J. Hazuda, John W. Shiver, and Antonello Pessi
Departments of *Antiviral Research and **Vaccine and Biologics Research, and §§Office of the President, Merck Research Laboratories, West Point, PA 19486; ¶Istituto di Ricerche di Biologia Molecolare “P. Angeletti,” 00040 Pomezia, Rome, Italy; and ||Cambridge Antibody Technology, Cambridge CB 16GH, United Kingdom
Contributed by Peter S. Kim, August 12, 2005
HIV-1 entry into cells is mediated by the envelope glycoprotein receptor-binding (gp120) and membrane fusion-promoting (gp41) subunits. The gp41 heptad repeat 1 (HR1) domain is the molecular target of the fusion-inhibitor drug enfuvirtide (T20). The HR1 sequence is highly conserved and therefore considered an attractive target for vaccine development, but it is unknown whether antibodies can access HR1. Herein, we use gp41-based peptides to select a human antibody, 5H/I1-BMV-D5 (D5), that binds to HR1 and inhibits the assembly of fusion intermediates in vitro. D5 inhibits the replication of diverse HIV-1 clinical isolates and therefore represents a previously unknown example of a crossneutralizing IgG selected by binding to designed antigens. NMR studies and functional analyses map the D5-binding site to a previously identified hydrophobic pocket situated in the HR1 groove. This hydrophobic pocket was proposed as a drug target and subsequently identified as a common binding site for peptide and peptidomimetic fusion inhibitors. The finding that the D5 fusion-inhibitory antibody shares the same binding site suggests that the hydrophobic pocket is a “hot spot” for fusion inhibition and an ideal target on which to focus a vaccine-elicited antibody response. Our data provide a structural framework for the design of new immunogens and therapeutic antibodies with crossneutralizing potential.
Abbreviations: HRn, heptad repeat n; 5H, five-helix; scFv, single-chain variable region fragment; HIVRP, HIV reporter particle; D5, 5H/I1-BMV-D5; T20, enfuvirtide.