. Author manuscript; available in PMC: 2016 Jul 9.

Published in final edited form as: J Mol Microbiol Biotechnol. 2015 Jul 9;25(0):73–78. doi: 10.1159/000381215

Table 2.

Four evolutionarily distinct families of PTS Enzyme IIC proteins and their characteristics

Enzyme family¹	Characteristics¹
A) The Glc-Fru-Lac Superfamily
1	Fru has been proposed to be the original PTS, but other IIC proteins diverged in function, sequence and possibly structure.
2	A basic dimeric 10 TMS topology, with two functionally different 5TMS halves per promoter is established for one member, but topological variations for other family members are possible.
3	IIAs and IIBs have mosaic origins; e.g. IIA^Glc is not homologous to IIA^Mtl, IIA^Ntr or IIA^Lac; IIB^Glc is not homologous to IIB^Chb.
4	IIAs, IIBs and IICs did not coevolve.
B) The Asc-Gat Superfamily
1	IIC^Asc homologues are often fused to IIA and IIB homologues, but IIC^Gat homologues never are. The IIC proteins have an 11 or 12 TMS topology, probably with a basic internal 6 TMS repeat unit, with an N-terminal TMS deleted for the 11 TMS proteins.
2	IIC^Asc homologues are always encoded by genes in operons with IIA and IIB genes, but IIC^Gat homologues can be encoded in operons lacking IIA and IIB genes.
3	Some IIC^Gat homologues are found in organisms that lack all other PTS proteins, suggesting roles as secondary carriers.
4	Asc and Gat IIA and IIB constituents are distantly related to IIA and IIB constituents of the Glc-Fru-Lac Superfamily
C) The Man Family
1	All constituents (IIA, IIB, IIC and IID) differ structurally from all other PTS permease proteins.
2	All members, but only members of this family, have IID constituents.
3	The IIB constituents are phosphorylated on His rather than Cys residues as is true for other IIB proteins.
4	Members often exhibit broad specificity for aldo- and keto- sugars.
D) The Dha Family
1	DhaK and DhaL are homologous to the N- and C-terminal domains of ATP-dependent dihydroxyacetone (DHA) kinases.
2	DhaM consists of three domains: IIA^Man-HPr-I Δ².
3	The three domains of DhaM are phosphorylated by PEP, EI and HPr, but DhaK and L are not phosphorylated.
4	DhaK binds DHA covalently to a His residue and transfers the phosphoryl group from IIA of DhaM via DhaL-ADP to DHA.

Abbreviations: Glc, glucose; Fru, fructose; Lac, lactose; Asc, L-ascorbate; Gat, galactitol; Man, mannose; Chb, diacelylchitobiose; Dha or DHA, dihydroxyacetone. See text and Figure 1 for protein designations.

I Δ, a truncated (partially deleted) Enzyme I.