title: Mimicking the structure of the V3 epitope bound to HIV-1 neutralizing antibodies.
abstract: The third variable region (V3) of the HIV-1 envelope glycoprotein gp120 is a target for virus neutralizing antibodies. The V3 sequence determines whether the virus will manifest R5 or X4 phenotypes and use the CCR5 or CXCR4 chemokine coreceptor, respectively. Previous NMR studies revealed that both R5- and X4-V3 peptides bound to antibodies 0.5beta and 447-52D form beta-hairpin conformations with the GPGR segment at the turn. In contrast, in their free form, linear V3 peptides and a cyclic peptide consisting of the entire 35-residue V3 loop were highly unstructured in aqueous solution. Herein we evaluated a series of synthetic disulfide constrained V3-peptides in which the position of the disulfide bonds, and therefore the ring size, was systematically varied. NMR structures determined for singly and doubly disulfide constrained V3-peptides in aqueous solution were compared with those found for unconstrained V3(JRFL) and V3(IIIB) peptides bound to 447-52D and to 0.5beta, respectively. Our study indicated that cyclic V3 peptides manifested significantly reduced conformational space compared to their linear homologues and that in all cases cyclic peptides exhibited cross-strand interactions suggestive of beta-hairpin-like structures. Nevertheless, the singly constrained V3-peptides retained significant flexibility and did not form an idealized beta-hairpin. Incorporation of a second disulfide bond results in significant overall rigidity, and in one case, a structure close to that of V3(MN) peptide bound to 447-52D Fab was assumed and in another case a structure close to that formed by the linear V3(IIIB) peptide bound to antibody 0.5beta was assumed.
authors.affiliation: Department of Structural Biology and Chemical Research Support Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Amit
authors.initials: A
authors.lastname: Mor
authors.forename: Eugenia
authors.initials: E
authors.lastname: Segal
authors.forename: Brenda
authors.initials: B
authors.lastname: Mester
authors.forename: Boris
authors.initials: B
authors.lastname: Arshava
authors.forename: Osnat
authors.initials: O
authors.lastname: Rosen
authors.forename: Fa-Xiang
authors.initials: FX
authors.lastname: Ding
authors.forename: Joseph
authors.initials: J
authors.lastname: Russo
authors.forename: Amnon
authors.initials: A
authors.lastname: Dafni
authors.forename: Fabian
authors.initials: F
authors.lastname: Schvartzman
authors.forename: Tali
authors.initials: T
authors.lastname: Scherf
authors.forename: Fred
authors.initials: F
authors.lastname: Naider
authors.forename: Jacob
authors.initials: J
authors.lastname: Anglister
mesh_terms: D000595:Amino Acid Sequence; D000914:Antibodies, Viral / Q000737:chemistry / Q000378:metabolism*; D001666:Binding Sites, Antibody; D004220:Disulfides; D000939:Epitopes / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D015699:HIV Envelope Protein gp120 / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D015497:HIV-1 / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D018716:Molecular Mimicry; D008969:Molecular Sequence Data; D009500:Neutralization Tests; D010455:Peptides / Q000138:chemical synthesis / Q000276:immunology / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D019713:Receptors, CCR5 / Q000378:metabolism; D019718:Receptors, CXCR4 / Q000378:metabolism
chemical_list: D000914:Antibodies, Viral; D004220:Disulfides; D000939:Epitopes; D015699:HIV Envelope Protein gp120; D010455:Peptides; D019713:Receptors, CCR5; D019718:Receptors, CXCR4