FIGURE 7.
Proposed reaction cycle of E. cloacae MurA involving the Cys-115-PEP adduct. The reaction cycle is derived from the different reaction states of MurA obtained by crystallography with wild-type or mutant enzyme liganded with UNAM, UNAG or UNAGal. The structure identifiers are the same as in Table 1. The cellular UNAG/UNAM ratio controls formation of the dormant complex I. Rapidly reversible exchange with UNAG yields complex II followed by transfer of PEP to UNAG to yield the tetrahedral intermediate, THI (III), which breaks down to the ternary products complex (IV). Covalent reaction of PEP with IV displaces Pi to yield complex V followed by rapidly reversible exchange of EP-UNAG and UNAG to complete the cycle. The PEP molecule is shown in cyan, the enolpyruvyl moiety is in green, and the muramic acid moiety is in magenta. The loop containing Cys-115 is shown in gray.