Department of Biochemistry and Molecular Pharmacology
Alleles; Amino Acid Sequence; Amino Acids; Carrier Proteins; Conserved Sequence; Exosomes; Models, Molecular; Molecular Sequence Data; Mutant Proteins; Mutation; Protein Binding; Protein Subunits; Protein Transport; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins
Life Sciences | Medicine and Health Sciences
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.
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Citation: Mol Biol Cell. 2009 Feb;20(3):973-82. Epub 2008 Dec 10. Link to article on publisher's site