A chaperone cascade sorts proteins for posttranslational membrane insertion into the endoplasmic reticulum.
Tail-anchored (TA) proteins are posttranslationally inserted into either the endoplasmic reticulum (ER) or the mitochondrial outer membrane. The C-terminal transmembrane domains (TMDs) of TA proteins enable their many essential cellular functions by specifying the membrane target, but how cells process these targeting signals is poorly understood. Here, we reveal the composition of a conserved multiprotein TMD recognition complex (TRC) and show that distinct TRC subunits recognize the two types of TMD signals. By engineering mutations in a mitochondrial TMD, we switch over its TRC subunit recognition, thus leading to its misinsertion into the ER. Biochemical reconstitution with purified components demonstrates that TRC tethers and enzymatically activates Get3 to selectively hand off ER-bound TA proteins to Get3. Thus, ER-bound TA proteins are sorted at the top of a TMD chaperone cascade that culminates with the formation of Get3-TA protein complexes, which are recruited to the ER membrane for insertion.
Wang
Fei
F
Department of Molecular and Cellular Biology, Harvard University, Northwest Labs, Cambridge, MA 02138, USA.
Brown
Emily C
EC
Mak
Gary
G
Zhuang
Jimmy
J
Denic
Vladimir
V
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000595:Amino Acid Sequence; D002352:Carrier Proteins / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D008565:Membrane Proteins; D024101:Mitochondrial Proteins / Q000378:metabolism; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D009154:Mutation; D021382:Protein Sorting Signals; D021122:Protein Subunits; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism
D002352:Carrier Proteins; C548889:GET4 protein, S cerevisiae; D020662:Guanine Nucleotide Exchange Factors; C510068:Mdy2 protein, S cerevisiae; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D018832:Molecular Chaperones; D046912:Multiprotein Complexes; D021382:Protein Sorting Signals; D021122:Protein Subunits; D029701:Saccharomyces cerevisiae Proteins; C520576:Sgt2 protein, S cerevisiae; D025801:Ubiquitin; D000251:Adenosine Triphosphatases; C529048:Get3 protein, S cerevisiae