BiP-mediated closing of the Sec61 channel limits Ca2+ leakage from the ER.
In mammalian cells, signal peptide-dependent protein transport into the endoplasmic reticulum (ER) is mediated by a dynamic protein-conducting channel, the Sec61 complex. Previous work has characterized the Sec61 channel as a potential ER Ca(2+) leak channel and identified calmodulin as limiting Ca(2+) leakage in a Ca(2+)-dependent manner by binding to an IQ motif in the cytosolic aminoterminus of Sec61α. Here, we manipulated the concentration of the ER lumenal chaperone BiP in cells in different ways and used live cell Ca(2+) imaging to monitor the effects of reduced levels of BiP on ER Ca(2+) leakage. Regardless of how the BiP concentration was lowered, the absence of available BiP led to increased Ca(2+) leakage via the Sec61 complex. When we replaced wild-type Sec61α with mutant Sec61αY344H in the same model cell, however, Ca(2+) leakage from the ER increased and was no longer affected by manipulation of the BiP concentration. Thus, BiP limits ER Ca(2+) leakage through the Sec61 complex by binding to the ER lumenal loop 7 of Sec61α in the vicinity of tyrosine 344.
Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany.
Nico
N
Schäuble
Sven
S
Lang
Martin
M
Jung
Sabine
S
Cappel
Stefan
S
Schorr
Özlem
Ö
Ulucan
Johannes
J
Linxweiler
Johanna
J
Dudek
Robert
R
Blum
Volkhard
V
Helms
Adrienne W
AW
Paton
James C
JC
Paton
Adolfo
A
Cavalié
Richard
R
Zimmermann
D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D000091342:Endoplasmic Reticulum Chaperone BiP; D020868:Gene Silencing / Q000502:physiology; D006367:HeLa Cells; D006360:Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects / Q000235:genetics; D017136:Ion Transport / Q000187:drug effects / Q000235:genetics; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D017510:Protein Folding / Q000187:drug effects; D034741:RNA, Small Interfering / Q000494:pharmacology; D000069816:SEC Translocation Channels
D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D034741:RNA, Small Interfering; D000069816:SEC Translocation Channels; C000613244:SEC61A1 protein, human; D002118:Calcium