title: Structure of the HIV-1 full-length capsid protein in a conformationally trapped unassembled state induced by small-molecule binding.
abstract: The capsid (CA) protein plays crucial roles in HIV infection and replication, essential to viral maturation. The absence of high-resolution structural data on unassembled CA hinders the development of antivirals effective in inhibiting assembly. Unlike enzymes that have targetable, functional substrate-binding sites, the CA does not have a known site that affects catalytic or other innate activity, which can be more readily targeted in drug development efforts. We report the crystal structure of the HIV-1 CA, revealing the domain organization in the context of the wild-type full-length (FL) unassembled CA. The FL CA adopts an antiparallel dimer configuration, exhibiting a domain organization sterically incompatible with capsid assembly. A small compound, generated in situ during crystallization, is bound tightly at a hinge site ("H site"), indicating that binding at this interdomain region stabilizes the ADP conformation. Electron microscopy studies on nascent crystals reveal both dimeric and hexameric lattices coexisting within a single condition, in agreement with the interconvertibility of oligomeric forms and supporting the feasibility of promoting assembly-incompetent dimeric states. Solution characterization in the presence of the H-site ligand shows predominantly unassembled dimeric CA, even under conditions that promote assembly. Our structure elucidation of the HIV-1 FL CA and characterization of a potential allosteric binding site provides three-dimensional views of an assembly-defective conformation, a state targeted in, and thus directly relevant to, inhibitor development. Based on our findings, we propose an unprecedented means of preventing CA assembly, by "conformationally trapping" CA in assembly-incompetent conformational states induced by H-site binding.
authors.affiliation: Department of Structural Biology, University of Pittsburgh Medical School, Pittsburgh, PA 15260, USA.
authors.forename: Shoucheng
authors.initials: S
authors.lastname: Du
authors.forename: Laurie
authors.initials: L
authors.lastname: Betts
authors.forename: Ruifeng
authors.initials: R
authors.lastname: Yang
authors.forename: Haibin
authors.initials: H
authors.lastname: Shi
authors.forename: Jason
authors.initials: J
authors.lastname: Concel
authors.forename: Jinwoo
authors.initials: J
authors.lastname: Ahn
authors.forename: Christopher
authors.initials: C
authors.lastname: Aiken
authors.forename: Peijun
authors.initials: P
authors.lastname: Zhang
authors.forename: Joanne I
authors.initials: JI
authors.lastname: Yeh
mesh_terms: D001665:Binding Sites; D036022:Capsid Proteins / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D015658:HIV Infections / Q000821:virology; D015497:HIV-1 / Q000737:chemistry* / Q000502:physiology; D006801:Humans; D008958:Models, Molecular; D015394:Molecular Structure; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D014779:Virus Replication; D054301:gag Gene Products, Human Immunodeficiency Virus / Q000737:chemistry* / Q000378:metabolism
chemical_list: D036022:Capsid Proteins; D054301:gag Gene Products, Human Immunodeficiency Virus