TY - JOUR
T1 - Identification of luminal loop 1 of scap protein as the sterol sensor that maintains cholesterol homeostasis
AU - Motamed, Massoud
AU - Zhang, Yinxin
AU - Wang, Michael L.
AU - Seemann, Joachim
AU - Kwon, Hyock Joo
AU - Goldstein, Joseph L.
AU - Brown, Michael S.
PY - 2011/5/20
Y1 - 2011/5/20
N2 - Cellular cholesterol homeostasis is maintained by Scap, an endoplasmic reticulum (ER) protein with eight transmembrane helices. In cholesterol-depleted cells, Scap transports sterol regulatory element-binding proteins (SREBPs) to the Golgi, where the active fragment of SREBP is liberated by proteases so that it can activate genes for cholesterol synthesis. When ER cholesterol increases, Scap binds cholesterol, and this changes the conformation of cytosolic Loop 6, which contains the binding site for COPII proteins. The altered conformation precludes COPII binding, abrogating movement to the Golgi. Consequently, cholesterol synthesis declines. Here, we identify the cholesterol-binding site on Scap as Loop 1, a 245-amino acid sequence that projects into the ER lumen. Recombinant Loop 1 binds sterols with a specificity identical to that of the entire Scap membrane domain. When tyrosine 234 in Loop 1 is mutated to alanine, Loop 6 assumes the cholesterol-bound conformation, even in sterol-depleted cells. As a result, full-length Scap(Y234A) cannot mediate SREBP processing in transfected cells. These results indicate that luminal Loop 1 of Scap controls the conformation of cytosolic Loop 6, thereby determining whether cells produce cholesterol.
AB - Cellular cholesterol homeostasis is maintained by Scap, an endoplasmic reticulum (ER) protein with eight transmembrane helices. In cholesterol-depleted cells, Scap transports sterol regulatory element-binding proteins (SREBPs) to the Golgi, where the active fragment of SREBP is liberated by proteases so that it can activate genes for cholesterol synthesis. When ER cholesterol increases, Scap binds cholesterol, and this changes the conformation of cytosolic Loop 6, which contains the binding site for COPII proteins. The altered conformation precludes COPII binding, abrogating movement to the Golgi. Consequently, cholesterol synthesis declines. Here, we identify the cholesterol-binding site on Scap as Loop 1, a 245-amino acid sequence that projects into the ER lumen. Recombinant Loop 1 binds sterols with a specificity identical to that of the entire Scap membrane domain. When tyrosine 234 in Loop 1 is mutated to alanine, Loop 6 assumes the cholesterol-bound conformation, even in sterol-depleted cells. As a result, full-length Scap(Y234A) cannot mediate SREBP processing in transfected cells. These results indicate that luminal Loop 1 of Scap controls the conformation of cytosolic Loop 6, thereby determining whether cells produce cholesterol.
UR - http://www.scopus.com/inward/record.url?scp=79955973156&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=79955973156&partnerID=8YFLogxK
U2 - 10.1074/jbc.M111.238311
DO - 10.1074/jbc.M111.238311
M3 - Article
C2 - 21454655
AN - SCOPUS:79955973156
SN - 0021-9258
VL - 286
SP - 18002
EP - 18012
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 20
ER -