title: Protease cleavage leads to formation of mature trimer interface in HIV-1 capsid.
abstract: During retrovirus particle maturation, the assembled Gag polyprotein is cleaved by the viral protease into matrix (MA), capsid (CA), and nucleocapsid (NC) proteins. To form the mature viral capsid, CA rearranges, resulting in a lattice composed of hexameric and pentameric CA units. Recent structural studies of assembled HIV-1 CA revealed several inter-subunit interfaces in the capsid lattice, including a three-fold interhexamer interface that is critical for proper capsid stability. Although a general architecture of immature particles has been provided by cryo-electron tomographic studies, the structural details of the immature particle and the maturation pathway remain unknown. Here, we used cryo-electron microscopy (cryoEM) to determine the structure of tubular assemblies of the HIV-1 CA-SP1-NC protein. Relative to the mature assembled CA structure, we observed a marked conformational difference in the position of the CA-CTD relative to the NTD in the CA-SP1-NC assembly, involving the flexible hinge connecting the two domains. This difference was verified via engineered disulfide crosslinking, revealing that inter-hexamer contacts, in particular those at the pseudo three-fold axis, are altered in the CA-SP1-NC assemblies compared to the CA assemblies. Results from crosslinking analyses of mature and immature HIV-1 particles containing the same Cys substitutions in the Gag protein are consistent with these findings. We further show that cleavage of preassembled CA-SP1-NC by HIV-1 protease in vitro leads to release of SP1 and NC without disassembly of the lattice. Collectively, our results indicate that the proteolytic cleavage of Gag leads to a structural reorganization of the polypeptide and creates the three-fold interhexamer interface, important for the formation of infectious HIV-1 particles.
authors.affiliation: Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States of America.
authors.forename: Xin
authors.initials: X
authors.lastname: Meng
authors.forename: Gongpu
authors.initials: G
authors.lastname: Zhao
authors.forename: Ernest
authors.initials: E
authors.lastname: Yufenyuy
authors.forename: Danxia
authors.initials: D
authors.lastname: Ke
authors.forename: Jiying
authors.initials: J
authors.lastname: Ning
authors.forename: Maria
authors.initials: M
authors.lastname: Delucia
authors.forename: Jinwoo
authors.initials: J
authors.lastname: Ahn
authors.forename: Angela M
authors.initials: AM
authors.lastname: Gronenborn
authors.forename: Christopher
authors.initials: C
authors.lastname: Aiken
authors.forename: Peijun
authors.initials: P
authors.lastname: Zhang
mesh_terms: D002213:Capsid / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*; D020285:Cryoelectron Microscopy / Q000379:methods; D016333:HIV Protease / Q000737:chemistry* / Q000378:metabolism; D015497:HIV-1 / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*; D055503:Protein Multimerization; D059748:Proteolysis; D054301:gag Gene Products, Human Immunodeficiency Virus / Q000737:chemistry* / Q000378:metabolism
chemical_list: D054301:gag Gene Products, Human Immunodeficiency Virus; D016333:HIV Protease; C514803:p16 protease, Human immunodeficiency virus 1