engleski

Structural investigations of amino acid:[carrier protein] ligases and their specificity for carrier proteins

Amino acid:[carrier protein] ligases (aa:CP ligases) are newly discovered bacterial homologues of atypical seryl-tRNA sythetases (aSerRS) which adopted a function different from attachment of serine to the cognate tRNA. aa:CP ligases covalently bind amino acid to the phosphopantetheine arm of the cognate carrier protein (CP). We have recently reported the structure of glycine:[carrier protein] ligase (Gly:CP ligase) from Bradyrhizobium japonicum. Gly:CP ligase lacks tRNA-binding domain and shows high similarity to the overall fold of aSerRS catalytic domain. To understand the recognition and binding of CP, the crystal structure of Gly:CP ligase complexed with CPGly was solved. CPGly binds to a specific helix of Gly:CP ligase, which is held on a long loop and exposed to the solvent. In Gly:CP ligase structure without CPGly, this helix seems to be disordered and always visible only in one subunit of the homodimer, due to crystal contacts. This suggests that the helix becomes ordered upon the binding of CPGly. To understand the specificity of aa:CP ligases for cognate CP, a hybrid protein was designed. The helix important for CP binding has been replaced with equivalent one from Ala:CP ligase from Agrobacterium tumefaciens. It was shown that the hybrid protein changed specificity for CP ; it catalyses covalent binding of Gly to CPAla. Structure of the hybrid protein complexed with CPAla has also been solved and shows different mode of binding than CPGly to Gly:CP ligase. Interestingly, CPAla binds in a slightly different orientation making different specific contacts with the ligase helix. These structures reveal molecular basis for discrimination of structurally highly similar carrier proteins.

amino acid:[carrier protein] ligase ; carrier protein ; biomacromolecular crystallography ; protein-protein interaction

nije evidentirano