Abstract
Mature HIV-1 viral particles assemble as a fullerene configuration comprising p24 capsid hexamers, pentamers and dimers. In this paper, we report the X-ray crystal structures of the p24 protein from natural HIV-1 strain (BMJ4) in complex with Fab A10F9, which recognizes a conserved epitope in the C-terminal domain of the BMJ4 p24 protein. Our structures reveal a novel shoulder-to-shoulder p24 dimerization mode that is mediated by an S-S bridge at C177. Consistent with these structures, the shoulder-to-shoulder dimer that was obtained from the BMJ4 strain was also observed in p24 proteins from other strains by the introduction of a cysteine residue at position 177. The potential biological significance was further validated by the introduction of a C177A mutation in the BMJ4 strain, which then displays a low infectivity. Our data suggest that this novel shoulder-to-shoulder dimer interface trapped by this unique S-S bridge could represent a physiologically relevant mode of HIV-1 capsid assembly during virus maturation, although Cys residue itself may not be critical for HIV-I replication.
Highlights
The mature HIV-1 capsid is a fullerene cone comprising approximately 250 hexamers and 12 pentamers of the viral CA protein (p24), with seven pentamers located at the broad end and five pentamers located at the narrow end [1,2,3,4]
HIV-1 p24 C-terminal domain (CTD) domains from different constructs have been crystallized into several distinct dimerization interfaces: the CTD domain with full affinity displays a side-byside conformation that is primarily stabilized by helix 9 [15], the CTD domain with a shorter construct displays a similar side-by-side dimer with a tilted dyad axis (2a8o) [6], a single amino acid residue deletion introduced in the helix 8/9 linker promotes a ‘‘domain-swapping’’ dimerization mode (2ont) [14], and an HIV-1 inhibitor bound to p24 CTD induces an ‘‘inert’’ CTD-CTD dimer that is incapable of extending the capsid lattice [16]
Several Fab fragment crystal structures of Monoclonal antibodies (mAbs) raised against HIV-1 p24 have been reported; some Fab fragments recognize the p24 N-terminal domain (NTD), whereas others recognize the p24 CTD [20,21,22]
Summary
The mature HIV-1 capsid is a fullerene cone comprising approximately 250 hexamers and 12 pentamers of the viral CA protein (p24), with seven pentamers located at the broad end and five pentamers located at the narrow end [1,2,3,4]. Crystallization of the full-length HIV-1 p24 protein is a difficult task because of the intrinsic flexibility of the linker region between the NTD and CTD, the weak interactions within hexamers and the tendency to form capsid-like particles [4,11,12] To overcome this technical difficulty, many approaches have been employed, including disulfide cross-linking by Cys mutations and dimerization promotion by deletion mutations. We describe crystal structures of the HIV-1 capsid p24 dimer from the BMJ4 strain in complex with the Fab fragment of the broad-spectrum antibody A10F9 with different space groups Our structures of these complexes demonstrate that A10F9 recognizes a continuous epitope located at a-helix 10 (residues 196 to residues 207) in the C-terminal domain of the BMJ4 p24 capsid protein. Our data suggest that the shoulder-to-shoulder dimer interface mediated by residue 177 could represent a physiologically relevant mode of HIV-1 capsid assembly during virus maturation, Cys residue itself may not be critical for HIV-1 replication
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
