title: Mutation of the SP1 sequence impairs both multimerization and membrane-binding activities of human immunodeficiency virus type 1 Gag.
abstract: The Gag protein of human immunodeficiency virus type 1 contains a 14-amino-acid region, termed SP1, between the capsid and downstream nucleocapsid sequences. Although SP1 is known to be indispensable for virus production, the mechanisms involved are mostly unclear. In this study, we demonstrate that an M368A mutation within SP1 severely diminished the ability of Gag to associate with cellular membranes. Although wild-type levels of membrane binding were restored to the M368A Gag by a second-site L20K mutation within matrix, the resultant Gag mutant L20K-M368A remained defective in virus production. This latter deficit was partially consequent to the binding of L20K-M368A Gag to nonraft membranes as opposed to raft association seen for wild-type Gag. Further analysis revealed that the majority of membrane-bound M368A Gag proteins were small oligomers, indicating a multimerization defect. In support of this observation, purified recombinant Gag derivatives containing the M368A mutation formed much lower amounts of high-molecular-weight complexes that were pelletable at 21,000 x g than did wild-type Gag. Based on the myristyl switch model, we propose that the M368A mutation inhibits Gag multimerization and, as a result, restricts the binding of Gag to cellular membranes.
authors.affiliation: McGill AIDS Centre, Lady Davis Institute-Jewish General Hospital, 3755 Cote Ste-Catherine Rd., Montreal, Quebec, Canada H3T 1E2.
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Guo
authors.forename: Ariel
authors.initials: A
authors.lastname: Roldan
authors.forename: Jing
authors.initials: J
authors.lastname: Hu
authors.forename: Mark A
authors.initials: MA
authors.lastname: Wainberg
authors.forename: Chen
authors.initials: C
authors.lastname: Liang
mesh_terms: D000818:Animals; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism*; D019281:Dimerization; D015967:Gene Expression Regulation, Viral; D015683:Gene Products, gag / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015497:HIV-1 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008561:Membrane Fusion; D009154:Mutation; D014162:Transfection; D019065:Virus Assembly
chemical_list: D015683:Gene Products, gag