Solution structure of a post-transition state analog of the phosphotransfer reaction between the A and B cytoplasmic domains of the te l-0 7, v er sio n - 2 M ay Résultats et discussion mannitol transporter IIMannitol of the Escherichia coli phosphotransf

The solution structure of the post-transition state complex between the isolated cytoplasmic A (IIAMtl) and phosphorylated B (phospho-IIBMtl) domains of the mannitol transporter of the Esch-erichia coli phosphotransferase system has been solved by NMR. The active site His-554 of IIAMtl was mutated to glutamine to block phosphoryl transfer activity, and the active site Cys-384 of IIBMtl (residues of IIBMtl are denoted in italic type) was substituted by serine to permit the formation of a stable phosphorylated form of IIBMtl. The two complementary interaction surfaces are predomi-nantly hydrophobic, and two methionines on IIBMtl, Met-388 and Met-393, serve as anchors by interacting with two deep pockets on the surface of IIAMtl.With the exception of a salt bridge between the conserved Arg-538 of IIAMtl and the phosphoryl group of phospho-IIBMtl, electrostatic interactions between the two proteins are lim-ited to the outer edges of the interface, are few in number, an