4.A.4 The PTS Glucitol (Gut) Family
The Gut family consists only of glucitol-specific porters, but these occur both in Gram-negative and Gram-positive bacteria. IIGut of E. coli consists of three proteins, a IIA protein, a putative 4 TMS IIC2 protein and a putative 4 TMS IIC1 protein (Nguyen et al., 2006). The N- and C-termini as well as the IIB domain may thereby be localized to the cell cytoplasm, but the topology has not been established experimentally. IIAGut is believed to be phosphorylated on a histidyl residue, while IIBGut is probably phosphorylated on a cysteyl residue. However, these possibilities have not been demonstrated experimentally.