Recently, a nontransporting enzyme II complex was characterized
in E. coli that phosphorylates dihydroxyacetone (DHA) at
the expense of PEP, using three soluble DHA-specific proteins in
addition to EI and HPr (25). The three components of the DHA
enzyme II complex are designated DhaK, DhaL, and DhaM. The
DhaM protein of E. coli is a tridomain protein consisting of an
N-terminal IIADha domain that is distantly related to IIAMan, a
central HPr domain, and a C-terminally truncated EI domain. All
three domains have been shown to be phosphorylated, using PEP
and the classical enzyme I and HPr proteins as phosphoryl donors.
The various currently recognized phosphoryl relay chains of
the PTS are depicted in Fig. 1A.