Protease cleavage leads to formation of mature trimer interface in HIV-1 capsid.

Protease cleavage leads to formation of mature trimer interface in HIV-1 capsid.

Blog Article

During retrovirus particle maturation, the assembled Gag polyprotein is cleaved by the viral protease into matrix (MA), HEMAVOL 2 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 Shellfish Forks 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.