C-terminal immunoglobulin-like domain of helical cell shape-determining peptidoglycan hydrolases, a metallo-carboxypeptidase. The structural elements of this domain form a Ca2+ binding-channel, the Ca2+ being co-ordinated by six ligand-atoms [1].

1: Structural basis for the recognition of muramyltripeptide by Helicobacter pylori Csd4, a D,L-carboxypeptidase controlling the helical cell shape. Kim HS, Kim J, Im HN, An DR, Lee M, Hesek D, Mobashery S, Kim JY, Cho K, Yoon HJ, Han BW, Lee BI, Suh SW; Acta Crystallogr D Biol Crystallogr. 2014;70:2800-2812. PMID:25372672