6pw7
From Proteopedia
X-ray crystal structure of C. elegans STIM EF-SAM domain
Structural highlights
Function[STIM1_CAEEL] Plays a role in mediating store-operated Ca(2+) entry (SOCE), a Ca(2+) influx following depletion of intracellular Ca(2+) stores. Acts as Ca(2+) sensor which upon Ca(2+) depletion, activates the Ca(2+) release-activated Ca(2+) (CRAC) channel subunit, orai-1. Essential for Ca (2+) and IP3-dependent contractile activity of gonad sheath cells and spermatheca. Essential for fertility. Does not play a role in posterior body wall muscle contraction (pBoc) rhythmicity, intestinal cell oscillatory Ca(2+) signaling or intestinal ER Ca(2+) hemeostasis.[1] [2] Publication Abstract from PubMedStore operated calcium (Ca(2+)) entry (SOCE) is the process whereby endoplasmic reticulum (ER) Ca(2+) store depletion causes Orai1-composed Ca(2+) channels on the plasma membrane (PM) to open, mediating a rise in cytosolic Ca(2+) levels. Stromal interaction molecules (STIM)s are the proteins that directly sense ER Ca(2+) content and gate Orai1 channels due to store depletion. The trigger for STIM activation is Ca(2+) unbinding from the ER lumen-oriented domains, which consist of a non-conserved amino (N) terminal region and EF-hand and sterile alpha motif (SAM) domains (EF-SAM), highly conserved from humans to Caenorhabditis elegans. Solution NMR structures of the human EF-SAM domains have been determined at high Ca(2+) concentrations; however, no direct structural view of the Ca(2+) binding mode has been elucidated. Further, no atomic resolution data currently exists on EF-SAM at low Ca(2+) levels. Here, we determined the X-ray crystal structure of the C. elegans STIM luminal domain, revealing that EF-SAM binds a single Ca(2+) ion with pentagonal bipyramidal geometry and an ancillary alpha-helix formed by the N-terminal region acts as a brace to stabilize EF-SAM. Using solution NMR, we observed EF-hand domain unfolding and a conformational exchange between folded and unfolded states involving the ancillary alpha-helix and the canonical EF-hand in low Ca(2+). Remarkably, we also detected an alpha-helix (+Ca(2+)) to beta-strand (-Ca(2+)) transition at the terminal SAM domain alpha-helix. Collectively, our analyses indicate that one canonically bound Ca(2+) ion is sufficient to stabilize the quiescent luminal domain structure, precluding unfolding, conformational exchange and secondary structure transformation. Coordination of a single calcium ion in the EF-hand maintains the off state of the stromal interaction molecule luminal domain.,Enomoto M, Nishikawa T, Back SI, Ishiyama N, Zheng L, Stathopulos PB, Ikura M J Mol Biol. 2019 Oct 15. pii: S0022-2836(19)30594-7. doi:, 10.1016/j.jmb.2019.10.003. PMID:31626806[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
| ||||||||||||||||||||||
