title: Terminal interface conformations modulate dimer stability prior to amino terminal autoprocessing of HIV-1 protease.
abstract: The HIV-1 protease (PR) mediates its own release (autoprocessing) from the polyprotein precursor, Gag-Pol, flanked by the transframe region (TFR) and reverse transcriptase at its N- and C-termini, respectively. Autoprocessing at the N-terminus of PR mediates stable dimer formation essential for catalytic activity, leading to the formation of infectious virus. An antiparallel β-sheet interface formed by the four N- and C-terminal residues of each subunit is important for dimer stability. Here, we present the first high-resolution crystal structures of model protease precursor-clinical inhibitor (PI darunavir or saquinavir) complexes, revealing varying conformations of the N-terminal flanking (S(-4)FNF(-1)) and interface residues (P(1)QIT(4)). A 180° rotation of the T(4)-L(5) peptide bond is accompanied by a new Q(2)-L(5) hydrogen bond and complete disengagement of PQIT from the β-sheet dimer interface, which may be a feature for intramolecular autoprocessing. This result is consistent with drastically lower thermal stability by 14-20 °C of PI complexes of precursors and the mature PR lacking its PQIT residues (by 18.3 °C). Similar to the TFR-PR precursor, this deletion also results in a darunavir dissociation constant (2 × 10(4))-fold higher and a markedly increased dimer dissociation constant relative to the mature PR. The terminal β-sheet perturbations of the dimeric structure likely account for the drastically poorer inhibition of autoprocessing of TFR-PR relative to the mature PR, even though significant differences in active site-PI interactions in these structures were not observed. The novel conformations of the dimer interface may be exploited to target selectively the protease precursor prior to its N-terminal cleavage.
authors.affiliation: Department of Biology, Molecular Basis of Disease Program, Georgia State University, Atlanta, Georgia 30303, United States.
authors.forename: Johnson
authors.initials: J
authors.lastname: Agniswamy
authors.forename: Jane M
authors.initials: JM
authors.lastname: Sayer
authors.forename: Irene T
authors.initials: IT
authors.lastname: Weber
authors.forename: John M
authors.initials: JM
authors.lastname: Louis
mesh_terms: D000595:Amino Acid Sequence; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004795:Enzyme Stability; D016333:HIV Protease / Q000737:chemistry* / Q000378:metabolism*; D006868:Hydrolysis; D008969:Molecular Sequence Data; D011487:Protein Conformation; D055503:Protein Multimerization; D011498:Protein Precursors / Q000737:chemistry; D011499:Protein Processing, Post-Translational; D055550:Protein Stability; D013816:Thermodynamics; D054301:gag Gene Products, Human Immunodeficiency Virus / Q000737:chemistry; D054302:pol Gene Products, Human Immunodeficiency Virus / Q000737:chemistry
chemical_list: D011498:Protein Precursors; D054301:gag Gene Products, Human Immunodeficiency Virus; D054302:pol Gene Products, Human Immunodeficiency Virus; D016333:HIV Protease; C514803:p16 protease, Human immunodeficiency virus 1