The short N-terminal domains of STIM1 and STIM2 control the activation kinetics of Orai1 channels.
STIM1 and STIM2 are dynamic transmembrane endoplasmic reticulum Ca(2+) sensors, coupling directly to activate plasma membrane Orai Ca(2+) entry channels. Despite extensive sequence homology, the STIM proteins are functionally distinct. We reveal that the short variable N-terminal random coil sequences of STIM1 and STIM2 confer profoundly different activation properties. Using Orai1-expressing HEK293 cells, chimeric replacement of the 43-amino-acid STIM1 N terminus with that of STIM2 attenuates Orai1-mediated Ca(2+) entry and drastically slows store-induced Orai1 channel activation. Conversely, the 55-amino-acid STIM2 terminus substituted within STIM1 strikingly enhances both Orai1-mediated Ca(2+) entry and constitutive coupling to activate Orai1 channels. Hence, STIM N termini are powerful coupling modifiers, functioning in STIM2 to "brake" the otherwise constitutive activation of Orai1 channels afforded by its high sensitivity to luminal Ca(2+).
Zhou
Yandong
Y
Department of Biochemistry, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
Mancarella
Salvatore
S
Wang
Youjun
Y
Yue
Chanyu
C
Ritchie
Michael
M
Gill
Donald L
DL
Soboloff
Jonathan
J
D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000235:genetics / Q000502:physiology*; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D007700:Kinetics; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000071740:ORAI1 Protein; D018408:Patch-Clamp Techniques; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D000071737:Stromal Interaction Molecule 1; D000071738:Stromal Interaction Molecule 2; D014162:Transfection
D015220:Calcium Channels; D015815:Cell Adhesion Molecules; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D000071740:ORAI1 Protein; C510746:ORAI1 protein, human; D011993:Recombinant Fusion Proteins; C103530:STIM1 protein, human; C513279:STIM2 protein, human; D000071737:Stromal Interaction Molecule 1; D000071738:Stromal Interaction Molecule 2; D002118:Calcium