This domain is found at the C-terminal end of a group of prokaryotic cation-chloride cotransporters (CCCs), including Na-K-Cl cotransporter from Methanosarcina acetivorans (Swiss:Q8THK8). These proteins consist of an N-terminal transmembrane transport region (Pfam:PF00324 and Pfam:PF13520) followed by a cytoplasmic regulatory domain. The C-terminal domain adopts a compact trapezoid-shaped elongated structure with a mixed alpha-beta fold and can be divided in two structurally related subdomains. This entry represents second subdomain, which shows a central five-stranded parallel beta-sheet and three alpha-helices that pack on either face of the sheet [1].

1: X-ray structure of the C-terminal domain of a prokaryotic cation-chloride cotransporter. Warmuth S, Zimmermann I, Dutzler R; Structure. 2009;17:538-546. PMID:19368887