1.C.126. The HlyC Haemolysin (HlyC) Family
The hemolysin C of Brachyspira hyodysenteriae (268 aas; ter Huurne et al., 1994; Hyatt and Joens 1997) and the Co2+-resistance protein, CorC of Salmonella typhimurium (273 aas; with one putative TMS (residues 163-181)) are homologous throughout most of their lengths to each other. They are also homologous to the C-terminal portions of 5 close paralogues in Bacillus subtilis, all of which are about 440 aas long and have an N-terminal 4 TMS domain. One representative B. subtilis paralogue is YrkA (434 aas; P54428). The CorC protein was believed to function as an auxiliary protein to the CorA Co2+/Mg2+ channel of S. typhimurium (Gibson et al., 1991). CorA is a member of the Metal Ion Transporter (MIT) family of α-type channels (TC #1.A.35). The HlyC family corresponds to SwissProt family UPF0053. MstE (1.A.26.1.2), CLC (2.A.49.6.1) and HlyC/CorC may all share a hydrophilic domain, and members of the HlyC family lack the 4 TMS transmembrane region and therefore are probably not transporters (see below).
The bacterial proteins, YrkA and YhdP have three recognized domains: the 4-TMS DUF21 domain (residues 1-170), a nucleotide binding CBS domain (residues 225-335) and a CorC/HlyC domain (residues 360-430). The mammalian homologues have at least the first two of these domains which are preceded by an N-terminal TMS and an unidentified hydrophilic domain. The bacterial HlyC and CorC proteins (1.C.126.1.1 and 1.C.126.1.2) lack the 4 TMS DUF21 domain, but have the CBS and CorC/HlyC domains. Only the proteins with the DUF21 domain are likely to be transporters. The evidence is consistent with the conclusion that these homologues form divalent-cation-specific porters, possibly exporters.