Solution structure of the phosphoryl transfer complex between the signal transducing proteins HPr and IIA(Glucose) of the Escherichia coli phosphoenolpyruvate : sugar phosphotransferase system

The solution structure of the second protein-protein complex of the Escheri chia coli phosphoenolpyruvate : sugar phosphotransferase system, that betwe en histidine-containing phosphocarrier protein (HPr) and glucose-specific e nzyme IIA(Glucose) (IIA(Glc)), has been determined by NMR spectroscopy, inc luding the use of dipolar couplings to provide long-range orientational inf ormation and newly developed rigid body minimization and constrained/restra ined simulated annealing methods. A protruding convex surface on HPr intera cts with a complementary concave depression on IIA(GlC). Both binding surfa ces comprise a central hydrophobic core region surrounded by a ring of pola r and charged residues, positive for HPr and negative for IIA(GlC). Formati on of the unphosphorylated complex, as well as the phosphorylated transitio n state, involves little or no change in the protein backbones, but there a re conformational rearrangements of the interfacial side chains. Both HPr a nd IIA(Glc) recognize a variety of structurally diverse proteins. Compariso ns with the structures of the enzyme I-HPr and IIA(Glc)-glycerol kinase com plexes reveal how similar binding surfaces can be formed with underlying ba ckbone scaffolds that are structurally dissimilar and highlight the role of redundancy and side chain conformational plasticity.