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Research Laboratories
Structural Virology Laboratory
Richard Wyatt, Ph.D.

Research Statement
A daunting task in the development of a broadly effective HIV-1 vaccine is to elicit humoral immune responses directed toward conserved, functional elements of the HIV-1 exterior envelope glycoprotein, gp120. Two functions common to virtually all HIV-1 gp120 glycoproteins are the ability to bind the primary virus receptor, CD4, and to bind to the more recently defined co-receptors. In a collaborative study, we have recently solved the crystal structure of gp120, in complex with CD4 and a neutralizing antibody. This structure uniquely provides us with insight regarding the means HIV-1 employs to mask these essential functional elements.

HIV-1 is tropic for CD4-positive cells by virtue of the high affinity interaction between the HIV-1 gp120 glycoprotein, and CD4, which acts as the primary virus receptor. The gp120 molecule is derived from a gp160 precursor glycoprotein and noncovalently associates with the transmembrane glycoprotein, gp41, to form trimeric complexes on the virus or cell surface. The mature HIV-1 gp120 is comprised of five regions conserved among viral strains (C1-C5) and five regions that exhibit considerable strain-to-strain variability (V1-V5). Besides CD4, HIV-1 requires co-factors to achieve entry into target cells. The second receptors used by HIV-1, primarily CXCR4 and CCR5, belong to a family of seven-membrane spanning, G-linked proteins which normally function as chemokine receptors.

Schematic representation of modifications used to produce soluble, stable HIV-1 trimeric envelope glycoproteins. The two R to S changes render the molecules cleavage-defective and maintain a covalent linkage between gp120 and gp41. These changes, in combination with the addition of GCN4 trimeric coiled coils, lend stability to the soluble envelope glycoproteins. The additional introduction of cysteine residues at positions 576 and 577 further increase the stability of the oligomers.

During the course of HIV-1 infection, neutralizing antibodies are elicited against various elements of gp120. Neutralizing antibodies appear to be an important component of the host immune response. Most clinical (primary) HIV-1 isolates are relatively resistant to neutralizing antibodies, suggesting that these viruses are selected by the presence of neutralizing antibodies in infected humans. In many HIV-1 infected individuals, two classes of neutralizing antibodies are elicited: strain-restricted and broadly cross-reactive antibodies. The strain-restricted antibodies appear early after infection and are generally directed against linear determinants within the gp120 third variable region. This class of antibodies has been relatively easy to generate in both primate and non-primate animal systems but are not broadly protective. A subset of the broadly-neutralizing antibodies recognize conformationally-dependent, discontinuous epitopes that overlap with the discontinuous CD4 binding site on gp120 and are termed CD4 binding site antibodies. A second limited subset of broadly-neutralizing antibodies recognize discontinuous gp120 epitopes, overlapping with the chemokine receptor binding site, that are better exposed upon CD4 binding and thus are referred to as CD4-induced antibodies. In naive individuals, the presence of broadly cross-reactive neutralizing antibodies and strain-restricted antibodies might help prevent or limit HIV-1 infection following exposure to the virus.

The broadly neutralizing antibodies, however, have been difficult to elicit in animals using wild-type gp120 glycoproteins as an immunogen. Through several hypotheses based upon evolving structural information of HIV-1 envelope glycoproteins, we will determine if rational modification of gp120 glycoproteins will influence the exposure and presentation of conserved, functional structures to the immune system. The elicitation of antibodies with an expanded breadth of neutralization capacity may thereby be enhanced. This rational approach to improve gp120 HIV-1 envelope glycoprotein immunogenicity may have a significant impact on HIV-1 vaccine design.

1. Wyatt R, Kwong P, Desjardins E, Sweet R, Robinson J, Hendrickson W and Sodroski J. The antigenic structure of the human immunodeficiency virus gp120 envelope glycoprotein. Nature 1998;393:705-11.
2. Kwong P, Wyatt R, Desjardins E, Sweet R, Robinson J, Sodroski J and Hendrickson W. Structure of an HIV gp120 envelope glycoprotein in complex with the CD4 and a neutralizing human antibody. Nature 1998;393:648-59.
3. Rizzuto C, Wyatt R, Hernandez-Ramos, Sun Y, Kwong P, Hendrickson W and Sodroski J. A conserved human immunodeficiency virus gp120 glycoprotein structure involved in chemokine receptor binding. Science 1998;280:1949-53.
4. Wyatt R and Sodroski J. The HIV-1 envelope glycoproteins: fusogens, antigens and immunogens. Science 1998;280:1884-88.
5. Farzan M, Choe H, Desjardins E, Sun Y, Kuhn J, Cao J, Wyatt R, and Sodroski J. Stabilization of HIV-1 envelope glycoprotein trimers by disulfide bonds introduced into the gp41 glycoprotein ectodomain. J Virol 1998;72:7620-25.
6. Kwong PD, Wyatt R, Desjardins E, Robinson J, Culp JS, Hellmig BD, Sweet RW, Sodroski J, Hendrickson WA. Probability analysis of variational crystallization and its application to gp120, the exterior envelope glycoprotein of type 1 human immunodeficiency virus (HIV-1). J Biol Chem 1999;274:4115-23.
7. Mirzabekov T, Bannert N, Farzan M, Hofmann W, Kolchinsky P, Wu L, Wyatt R, Sodroski J. Enhanced expression, native purification, and characterization of CCR5, a principal HIV-1 coreceptor. J Biol Chem 1999;274:28745-50.
8. Kwong PD, Wyatt R, Sattentau QJ, Sodroski J and Hendrickson WA. Oligomeric modeling and electrostatic analysis of the gp120 envelope glycoprotein of human immunodeficiency virus. J Virol 2000;74:1961-72.
9. Yang X, Florin L, Farzan M, Kolchinsky P, Kwong PD, Sodroski J and Wyatt R. Modifications that stabilize human immunodeficiency virus envelope glycoprotein trimers in solution. J Virol 2000;74:4746-4754.
10. Myszka DG, Sweet RW, Hensley P, Birgham-Burke M, Kwong PD, Hendrickson WA, Wyatt R, Sodroski J and Doyle M. Energetics of the HIV gp120-CD4 Binding Reaction. Energetics of the HIV gp120-CD4 binding reaction. Proc Natl Acad Sci U S A. 2000 Aug 1;97(16):9026-31
11. Koch M, Kwong PD, Kolchinsky P, Wang L,Hendrickson W Sodroski J and Wyatt R. Structure-based, Targeted Deglycosylation of the HIV-1 Exterior Envelope Glycoprotein, gp120, and Effects on Neutralization Sensitivity. Submitted.

If you are interested in a Research Fellowship, please send your CV to: Dr. Richard Wyatt NIH/Vaccine Research Center 40 Convent Drive Bldg. 40, Room 4512 Bethesda, MD 20892-3005 Email: richw@mail.nih.gov