STIM Protein Coupling Domains and The Activation of Orai Channels

STIM1 and STIM2 are widely expressed endoplasmic reticulum (ER) Ca2+ sensor proteins able to translocate within the ER membrane to physically couple with and gate plasma membrane (PM) Orai Ca2+ channels. The coupling of STIM proteins and Orai Ca2+ entry channels generates “store-operated” Ca2+ signals crucial in controlling responses in many cell types. In this study, we reveal critical differences in the function of the short STIM-Orai activating regions (SOAR) from STIM1 and STIM2. We narrowed these differences in Orai1 gating to a strategically exposed phenylalanine residue (Phe-394) in SOAR1, which in SOAR2 is substituted by a leucine residue. Remarkably, in full-length STIM1, replacement of Phe-394 with the dimensionally similar but polar histidine head-group, prevents both Orai1 binding and gating, creating an Orai1 non-agonist. Thus, this residue is critical in tuning the efficacy of Orai activation. While STIM1 is a full Orai1-agonist, leucine-replacement of this crucial residue in STIM2 endows it with partial agonist properties, which may be critical for limiting Orai1 activation stemming from its enhanced sensitivity to store-depletion. The dimeric derivative of 2-aminoethoxydiphenyl borinate (2-APB), DPB162-AE, blocks functional coupling between STIM1 and Orai1 with an IC50 (200 nM) 100-fold lower than 2-APB. Unlike 2-APB, DPB162-AE does not affect L-type or TRPC channels or Ca2+ pumps at maximal STIM1-Orai1 blocking levels. DPB162-AE blocks STIM1-induced Orai1 or Orai2, but does not block Orai3 or STIM2-mediated effects. We narrowed the DPB162-AE site of action to the STIM-Orai activating region (SOAR) of STIM1. DPB162-AE does not prevent the SOAR-Orai1 interaction but potently blocks SOAR-mediated Orai1 channel activation, yet its action is not as an Orai1 channel pore blocker. Using the SOAR-F394H mutant which prevents both physical and functional coupling to Orai1, we reveal DPB162-AE rapidly restores SOAR-Orai binding but only slowly restores Orai1 channel-mediated Ca2+ entry. With the same SOAR mutant, 2-APB induces rapid physical and functional coupling to Orai1, but channel activation is transient. We infer that the actions of both 2-APB and DPB162-AE are directed toward the STIM1-Orai1 coupling interface. Compared to 2-APB, DPB162-AE is a much more potent and specific STIM1/Orai1 functional uncoupler. DPB162-AE provides an important pharmacological tool and a useful mechanistic probe for the function and coupling between STIM1 and Orai1 channels.

Grantor dc:publisher

Temple University. Libraries

Year dc:date.issued

2015

Author dc:creator

• Wang, Xizhuo

Advisor dc:contributor.advisor

• Chong, Parkson Lee-Gau

Committee members dc:contributor.committeemember

• Gill, Donald L.
• Soboloff, Jonathan
• Muniswamy, Madesh

• Biochemistry

Statement dc:rights

• IN COPYRIGHT- This Rights Statement can be used for an Item that is in copyright. Using this statement implies that the organization making this Item available has determined that the Item is in copyright and either is the rights-holder, has obtained permission from the rights-holder(s) to make their Work(s) available, or makes the Item available under an exception or limitation to copyright (including Fair Use) that entitles it to make the Item available.

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

eng

Dc Identifier Other

958157382

OAI identifier oai:identifier

oai:scholarshare.temple.edu:20.500.12613/4009