Sbh1p, a subunit of the Sec61 translocon, interacts with the chaperone calnexin in the yeast Yarrowia lipolytica.
The core component of the translocation apparatus, Sec61p or alpha, was previously cloned in Yarrowia lipolytica. Using anti-Sec61p antibodies, we showed that most of the translocation sites are devoted to co-translational translocation in this yeast, which is similar to the situation in mammalian cells but in contrast to the situation in Saccharomyces cerevisiae, where post-translational translocation is predominant. In order to characterize further the minimal translocation apparatus in Y. lipolytica, the beta Sec61 complex subunit, Sbh1p, was cloned by functional complementation of a Deltasbh1, Deltasbh2 S. cerevisiae mutant. The secretion of the reporter protein is not impaired in the Y. lipolytica sbh1 inactivated strain. We screened the Y. lipolytica two-hybrid library to look for partners of this translocon component. The ER-membrane chaperone protein, calnexin, was identified as an interacting protein. By a co-immunoprecipitation approach, we confirmed this association in Yarrowia and then showed that the S. cerevisiae Sbh2p protein was a functional homologue of YlSbh1p. The interaction of Sbh1p with calnexin was shown to occur between the lumenal domain of both proteins. These results suggest that the beta subunit of the Sec61 translocon may relay folding of nascent proteins to their translocation.
Boisramé
Anita
A
Laboratoire de Génétique moléculaire et cellulaire, INRA, CNRS, Institut National Agronomique Paris-Grignon, 78850 Thiverval-Grignon, France. boirame@grignon.inra.fr
Chasles
Marion
M
Babour
Anna
A
Beckerich
Jean-Marie
JM
Gaillardin
Claude
C
D000595:Amino Acid Sequence; D001483:Base Sequence; D037281:Calnexin / Q000378:metabolism*; D003001:Cloning, Molecular; D017931:DNA Primers; D018076:DNA, Complementary; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism*; D008969:Molecular Sequence Data; D011485:Protein Binding; D017510:Protein Folding; D000069816:SEC Translocation Channels; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D020798:Two-Hybrid System Techniques; D033921:Vesicular Transport Proteins; D025062:Yarrowia / Q000378:metabolism*
D017931:DNA Primers; D018076:DNA, Complementary; D008565:Membrane Proteins; D018832:Molecular Chaperones; D000069816:SEC Translocation Channels; C096367:SEC16 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C101188:Sbh1 protein, S cerevisiae; D033921:Vesicular Transport Proteins; D037281:Calnexin