title: Structure of the N-terminal 283-residue fragment of the immature HIV-1 Gag polyprotein.
abstract: The capsid protein (CA) of the mature human immunodeficiency virus (HIV) contains an N-terminal beta-hairpin that is essential for formation of the capsid core particle. CA is generated by proteolytic cleavage of the Gag precursor polyprotein during viral maturation. We have determined the NMR structure of a 283-residue N-terminal fragment of immature HIV-1 Gag (Gag(283)), which includes the intact matrix (MA) and N-terminal capsid (CA(N)) domains. The beta-hairpin is unfolded in Gag(283), consistent with the proposal that hairpin formation occurs subsequent to proteolytic cleavage of Gag, triggering capsid assembly. Comparison of the immature and mature CA(N) structures reveals that beta-hairpin formation induces a approximately 2 A displacement of helix 6 and a concomitant displacement of the cyclophylin-A (CypA)-binding loop, suggesting a possible allosteric mechanism for CypA-mediated destabilization of the capsid particle during infectivity.
authors.affiliation: Howard Hughes Medical Institute and Department of Chemistry and Biochemistry, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, USA.
authors.forename: Chun
authors.initials: C
authors.lastname: Tang
authors.forename: Yasmine
authors.initials: Y
authors.lastname: Ndassa
authors.forename: Michael F
authors.initials: MF
authors.lastname: Summers
mesh_terms: D000595:Amino Acid Sequence; D021984:Cyclophilin A / Q000378:metabolism; D015683:Gene Products, gag / Q000737:chemistry* / Q000378:metabolism; D015488:HIV Antigens / Q000737:chemistry; D015497:HIV-1 / Q000737:chemistry* / Q000254:growth & development / Q000502:physiology / Q000648:ultrastructure; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D019590:Nucleocapsid Proteins; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism; D011498:Protein Precursors / Q000737:chemistry* / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D014764:Viral Proteins; D019065:Virus Assembly; D054301:gag Gene Products, Human Immunodeficiency Virus
chemical_list: D015683:Gene Products, gag; D015488:HIV Antigens; D019590:Nucleocapsid Proteins; D010446:Peptide Fragments; D011498:Protein Precursors; D014764:Viral Proteins; D054301:gag Gene Products, Human Immunodeficiency Virus; C060295:p15 gag protein, Human immunodeficiency virus 1; C054858:p17 protein, Human Immunodeficiency Virus Type 1; C059767:p55 gag precursor protein, Human immunodeficiency virus 1; D021984:Cyclophilin A