Mutations in the Sec61p channel affecting signal sequence recognition and membrane protein topology.
The orientation of most single-spanning membrane proteins obeys the "positive-inside rule", i.e. the flanking region of the transmembrane segment that is more positively charged remains in the cytosol. These membrane proteins are integrated by the Sec61/SecY translocon, but how their orientation is achieved is unknown. We have screened for mutations in yeast Sec61p that alter the orientation of single-spanning membrane proteins. We identified a class of mutants that are less efficient in retaining the positively charged flanking region in the cytosol. Surprisingly, these mutations are located at many different sites in the Sec61/SecY molecule, and they do not only involve charged amino acid residues. All these mutants have a prl phenotype that so far have only been seen in bacteria; they allow proteins with defective signal sequences to be translocated, likely because the Sec61p channel opens more easily. A similar correlation between topology defects and prl phenotype was also seen with previously identified yeast Sec61 mutants. Our results suggest a model in which the regulated opening of the translocon is required for the faithful orientation of membrane proteins.
Junne
Tina
T
Biozentrum, University of Basel, Klingelbergstrasse 70, Basel, Switzerland.
Schwede
Torsten
T
Goder
Veit
V
Spiess
Martin
M
D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D026901:Membrane Transport Proteins; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D021382:Protein Sorting Signals / Q000235:genetics*; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D000069816:SEC Translocation Channels; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*
D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D021382:Protein Sorting Signals; D000069816:SEC Translocation Channels; C499383:SEC61 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins