Sec6p anchors the assembled exocyst complex at sites of secretion.
The exocyst is an essential protein complex required for targeting and fusion of secretory vesicles to sites of exocytosis at the plasma membrane. To study the function of the exocyst complex, we performed a structure-based mutational analysis of the Saccharomyces cerevisiae exocyst subunit Sec6p. Two "patches" of highly conserved residues are present on the surface of Sec6p; mutation of either patch does not compromise protein stability. Nevertheless, replacement of SEC6 with the patch mutants results in severe temperature-sensitive growth and secretion defects. At nonpermissive conditions, although trafficking of secretory vesicles to the plasma membrane is unimpaired, none of the exocyst subunits are polarized. This is consistent with data from other exocyst temperature-sensitive mutants, which disrupt the integrity of the complex. Surprisingly, however, these patch mutations result in mislocalized exocyst complexes that remain intact. Our results indicate that assembly and polarization of the exocyst are functionally separable events, and that Sec6p is required to anchor exocyst complexes at sites of secretion.
Songer
Jennifer A
JA
Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, USA.
Munson
Mary
M
D000483:Alleles; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D017124:Conserved Sequence; D055354:Exosomes / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D021122:Protein Subunits / Q000378:metabolism; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism*; D033921:Vesicular Transport Proteins
D000596:Amino Acids; D002352:Carrier Proteins; D050505:Mutant Proteins; D021122:Protein Subunits; C490684:SEC6 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins