4.A.5 The PTS Galactitol (Gat) Family

The only well-characterized member of the Gat famly is the galactitol permease of E. coli (Noblemann and Lengeler, 1995). However, a homologous IIC protein (38% identity) from Listeria monocytogenes has been shown to be required for D-arabitol fermentation (Saklani-Jusforgues et al., 2001). It functions together with IIA^Gat and IIB^Gat homologues. IIC^Gat is distantly related to IIC^Sgc of E. coli (Reizer et al., 1996); IIA^Gat is distantly related to IIA^Sga and IIA^Sgc of E. coli as well as IIA^Mtl and IIA^Fru. IIB^Gat is distantly related to IIB^Sga and IIB^Sgc of E. coli. Domains in the LicR/CelR family of transcriptional activators show C-terminal domains exhibiting weak sequence similiarity to IIB^Gat and IIA^Gat (Tchieu et al., 2001). The biochemistry of this family is poorly defined. Howeever, the 3-d structure of GatB has been solved. GatB consists of a central four-stranded parallel beta-sheet flanked by alpha-helices on both sides. The active site cysteine of GatB is located at the beginning of an unstructured loop between beta1 and alpha1 that folds into a P-loop-like structure. This structural arrangement shows similarities with other IIB subunits as noted above, but also with mammalian low molecular weight protein tyrosine phosphatases (LMW PTPase) and arsenate reductase (ArsC) (Volpon et al. 2006).The Gat Family is related to the L-Asc Family (TC# 4.A.7) (Hvorup et al. 2003; Saier et al. 2005).