4KJS

Structure of native YfkE

Summary for 4KJS

• Entry DOI: 10.2210/pdb4kjs/pdb
• Related: 4KJR
• Descriptor: cation exchanger YfkE (2 entities in total)
• Functional Keywords: yfke, caca, ca/h+ antiporter, cax, transport protein
• Biological source: Bacillus subtilis subsp. subtilis
• Cellular location: Cell membrane; Multi-pass membrane protein (Potential): O34840
• Total number of polymer chains: 2
• Total formula weight: 75004.37

Authors

Wu, M.,Tong, S.,Zheng, L. (deposition date: 2013-05-03, release date: 2013-06-26, Last modification date: 2024-02-28)

Primary citation

Wu, M.,Tong, S.,Waltersperger, S.,Diederichs, K.,Wang, M.,Zheng, L.
Crystal structure of Ca2+/H+ antiporter protein YfkE reveals the mechanisms of Ca2+ efflux and its pH regulation.
Proc.Natl.Acad.Sci.USA, 110:11367-11372, 2013

PubMed 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.

PubMed: 23798403
DOI: 10.1073/pnas.1302515110

Experimental method

X-RAY DIFFRACTION (3.05 Å)