Palmitoylation of the intracytoplasmic R peptide of the transmembrane envelope protein in Moloney murine leukemia virus.
Previously it was reported that the 16-amino-acid (aa) C-terminal cytoplasmic tail of Moloney murine leukemia virus (MoMLV) transmembrane protein Pr15E is cleaved off during virus synthesis, yielding the mature, fusion active transmembrane protein p15E and the 16-aa peptide (R peptide or p2E). It remains to be elucidated how the R peptide impairs fusion activity of the uncleaved Pr15E. The R peptide from MoMLV was analyzed by Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunostained with antiserum against the synthetic 16-aa R peptide. The R peptide resolved with an apparent molecular mass of 7 kDa and not the 4 kDa seen with the corresponding synthetic peptide. The 7-kDa R peptide was found to be membrane bound in MoMLV-infected NIH 3T3 cells, showing that cleavage of the 7-kDa R-peptide tail must occur before or during budding of progeny virions, in which only small amounts of the 7-kDa R peptide were found. The 7-kDa R peptide was palmitoylated since it could be labeled with [(3)H]palmitic acid, which explains its membrane association, slower migration on gels, and high sensitivity in immunoblotting. The present results are in contrast to previous findings showing equimolar amounts of R peptide and p15E in virions. The discrepancy, however, can be explained by the presence of nonpalmitoylated R peptide in virions, which were poorly detected by immunoblotting. A mechanistic model is proposed. The uncleaved R peptide can, due to its lipid modification, control the conformation of the ectodomain of the transmembrane protein and thereby govern membrane fusion.
Olsen
K E
KE
Department of Pharmacology, The Royal Danish School of Pharmacy, DK-2100 Copenhagen O, Denmark.
Andersen
K B
KB
D016475:3T3 Cells; D000818:Animals; D003593:Cytoplasm / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel / Q000379:methods; D015151:Immunoblotting; D051379:Mice; D008970:Molecular Weight; D008979:Moloney murine leukemia virus / Q000378:metabolism*; D019308:Palmitic Acid / Q000378:metabolism*; D010455:Peptides / Q000138:chemical synthesis; D015682:Retroviridae Proteins, Oncogenic / Q000737:chemistry / Q000378:metabolism*; D013347:Subcellular Fractions; D014759:Viral Envelope Proteins / Q000737:chemistry / Q000378:metabolism; D014763:Viral Matrix Proteins / Q000737:chemistry / Q000378:metabolism*
D010455:Peptides; D015682:Retroviridae Proteins, Oncogenic; D014759:Viral Envelope Proteins; D014763:Viral Matrix Proteins; C085823:murine leukemia virus protein p2E; C078678:p15E protein, Murine leukemia virus; D019308:Palmitic Acid