This domain contains three transmembrane helices. Proteins containing this domain are important for glycine utilisation, being identified as glycine transporters. Some members of the family are also important for alanine utilisation. In these proteins this domain is found in pairs [1]. An archaeal member of this family which contains this domain is a TRIC-type potassium channel [2].

1: Mutant phenotypes for thousands of bacterial genes of unknown function. Price MN, Wetmore KM, Waters RJ, Callaghan M, Ray J, Liu H, Kuehl JV, Melnyk RA, Lamson JS, Suh Y, Carlson HK, Esquivel Z, Sadeeshkumar H, Chakraborty R, Zane GM, Rubin BE, Wall JD, Visel A, Bristow J, Blow MJ, Arkin AP, Deutschbauer AM; Nature. 2018;557:503-509. PMID:29769716

2: Structural basis for conductance through TRIC cation channels. Su M, Gao F, Yuan Q, Mao Y, Li DL, Guo Y, Yang C, Wang XH, Bruni R, Kloss B, Zhao H, Zeng Y, Zhang FB, Marks AR, Hendrickson WA, Chen YH; Nat Commun. 2017;8:15103. PMID:28524849