Fig. 4.

Three topological types identified for ABC3 porters. a The basic four-TMS unit may or may not be fused N-terminally to an ABC (ATP-hydrolyzing) domain, but the eight- and 10-TMS proteins are never fused to ABC domains (Khwaja et al. 2005). b Two putative topological types with eight and 10 TMSs, respectively, resulting from intragenic duplication of the four-TMS unit shown in a. The two extra TMSs (in white) in the 10-TMS proteins are centrally located between the two repeat units. (Reproduced from Khwaja et al. 2005, with permission.)