Ergosterol content specifies targeting of tail-anchored proteins to mitochondrial outer membranes.
Tail-anchored (TA) proteins have a single C-terminal transmembrane domain, making their biogenesis dependent on posttranslational translocation. Despite their importance, no dedicated insertion machinery has been uncovered for mitochondrial outer membrane (MOM) TA proteins. To decipher the molecular mechanisms guiding MOM TA protein insertion, we performed two independent systematic microscopic screens in which we visualized the localization of model MOM TA proteins on the background of mutants in all yeast genes. We could find no mutant in which insertion was completely blocked. However, both screens demonstrated that MOM TA proteins were partially localized to the endoplasmic reticulum (ER) in spf1 cells. Spf1, an ER ATPase with unknown function, is the first protein shown to affect MOM TA protein insertion. We found that ER membranes in spf1 cells become similar in their ergosterol content to mitochondrial membranes. Indeed, when we visualized MOM TA protein distribution in yeast strains with reduced ergosterol content, they phenocopied the loss of Spf1. We therefore suggest that the inherent differences in membrane composition between organelle membranes are sufficient to determine membrane integration specificity in a eukaryotic cell.
Interfaculty Institute of Biochemistry, University of Tübingen, 72076 Tübingen, Germany.
Katrin
K
Krumpe
Idan
I
Frumkin
Yonatan
Y
Herzig
Nitzan
N
Rimon
Cagakan
C
Özbalci
Britta
B
Brügger
Doron
D
Rapaport
Maya
M
Schuldiner
D004721:Endoplasmic Reticulum / Q000378:metabolism; D004875:Ergosterol / Q000378:metabolism*; D017353:Gene Deletion; D049452:Green Fluorescent Proteins / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D051336:Mitochondrial Membranes / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism*
D029701:Saccharomyces cerevisiae Proteins; D049452:Green Fluorescent Proteins; D004875:Ergosterol