Solution NMR Structures of Productive and Non-productive Complexes between the A and B Domains of the Cytoplasmic Subunit of the Mannose Transporter of the Escherichia coli

Solution structures of complexes between the isolated A (IIAMan) and B (IIBMan) domains of the cytoplasmic component of the mannose transporter of Escherichia coli have been solved by NMR. The complex of wild-type IIAMan and IIBMan is amixture of two species comprising a productive, phosphoryl transfer compe-tent complex and a non-productive complex with the two active site histidines, His-10 of IIAMan and His-175 of IIBMan, separated by25 Å.Mutationof the active site histidine,His-10, of IIAMan to a glutamate, tomimic phosphorylation, results in the formation of a single productive complex. The apparent equilibrium dissocia-tion constants for the binding of both wild-type and H10E IIAMan to IIBMan are approximately the same (KD 0.5mM). The produc-tive complex can readily accommodate a transition state involving a pentacoordinate phosphoryl group with trigonal bipyramidal geometrybonded to theN2atomofHis-10of IIAMan and theN