Binding of human immunodeficiency virus type 1 Gag to membrane: role of the matrix amino terminus.
Binding of the human immunodeficiency virus type 1 (HIV-1) Gag protein precursor, Pr55(Gag), to membrane is an indispensable step in virus assembly. Previously, we reported that a matrix (MA) residue 6 substitution (6VR) imposed a virus assembly defect similar to that observed with myristylation-defective mutants, suggesting that the 6VR change impaired membrane binding. Intriguingly, the 6VR mutation had no effect on Gag myristylation. The defective phenotype imposed by 6VR was reversed by changes at other positions in MA, including residue 97. In this study, we use several biochemical methods to demonstrate that the residue 6 mutation, as well as additional substitutions in MA amino acids 7 and 8, reduce membrane binding without affecting N-terminal myristylation. This effect is observed in the context of Pr55(Gag), a truncated Gag containing only MA and CA, and in MA itself. The membrane binding defect imposed by the 6VR mutation is reversed by second-site changes in MA residues 20 and 97, both of which, when present alone, increase membrane binding to levels greater than those for the wild type. Both reduced and enhanced membrane binding imposed by the MA substitutions depend upon the presence of the N-terminal myristate. The results support the myristyl switch model recently proposed for the regulation of Gag membrane binding, according to which membrane binding is determined by the degree of exposure or sequestration of the N-terminal myristate moiety. Alternatively, insertion of the myristate into the lipid bilayer might be a prerequisite event for the function of other distinct MA-encoded membrane binding domains.
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Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892-0460, USA.
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D000595:Amino Acid Sequence; D002213:Capsid / Q000378:metabolism; D036022:Capsid Proteins; D002462:Cell Membrane / Q000378:metabolism; D015683:Gene Products, gag / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D015488:HIV Antigens / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015497:HIV-1 / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D016296:Mutagenesis; D019814:Myristic Acid / Q000378:metabolism; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism*; D014764:Viral Proteins; D019065:Virus Assembly; D054301:gag Gene Products, Human Immunodeficiency Virus
D036022:Capsid Proteins; D015683:Gene Products, gag; D015488:HIV Antigens; C071884:NCP7 protein, Human immunodeficiency virus 1; D011498:Protein Precursors; D014764:Viral Proteins; D054301:gag Gene Products, Human Immunodeficiency Virus; C054858:p17 protein, Human Immunodeficiency Virus Type 1; C059767:p55 gag precursor protein, Human immunodeficiency virus 1; D019814:Myristic Acid