This is the central, beta-barrel, domain of the metallo-carboxypeptidase that maintains helical cell-shape in Helicobacter. It shows a novel fold. It has a highly positively charged surface which contributes to a high overall isoelectric point. A calcium-binding channel is formed from residues in the C-terminal Ig-like domain in conjunction with some of the long side-chains of residues from strands beta-14 and beta-18 of this domain [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