In:
Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 110, No. 28 ( 2013-07-09), p. 11367-11372
Abstract:
Ca 2+ efflux by Ca 2+ cation antiporter (CaCA) proteins is important for maintenance of Ca 2+ homeostasis across the cell membrane. Recently, the monomeric structure of the prokaryotic Na + /Ca 2+ exchanger (NCX) antiporter NCX_Mj protein from Methanococcus jannaschii shows an outward-facing conformation suggesting a hypothesis of alternating substrate access for Ca 2+ efflux. To demonstrate conformational changes essential for the CaCA mechanism, we present the crystal structure of the Ca 2+ /H + antiporter protein YfkE from Bacillus subtilis at 3.1-Å resolution. YfkE forms a homotrimer, confirmed by disulfide crosslinking. The protonated state of YfkE exhibits an inward-facing conformation with a large hydrophilic cavity opening to the cytoplasm in each protomer and ending in the middle of the membrane at the Ca 2+ -binding site. A hydrophobic “seal” closes its periplasmic exit. Four conserved α-repeat helices assemble in an X-like conformation to form a Ca 2+ /H + exchange pathway. In the Ca 2+ -binding site, two essential glutamate residues exhibit different conformations compared with their counterparts in NCX_Mj, whereas several amino acid substitutions occlude the Na + -binding sites. The structural differences between the inward-facing YfkE and the outward-facing NCX_Mj suggest that the conformational transition is triggered by the rotation of the kink angles of transmembrane helices 2 and 7 and is mediated by large conformational changes in their adjacent transmembrane helices 1 and 6. Our structural and mutational analyses not only establish structural bases for mechanisms of Ca 2+ /H + exchange and its pH regulation but also shed light on the evolutionary adaptation to different energy modes in the CaCA protein family.
Type of Medium:
Online Resource
ISSN:
0027-8424
,
1091-6490
DOI:
10.1073/pnas.1302515110
Language:
English
Publisher:
Proceedings of the National Academy of Sciences
Publication Date:
2013
detail.hit.zdb_id:
209104-5
detail.hit.zdb_id:
1461794-8
SSG:
11
SSG:
12
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