5N9X: Structure of adenylation domain THR1 involved in the biosynthesis of 4-chlorothreonine in Streptomyces SP.OH-5093, ligand bound structure

We determined the crystal structure of Thr1, the self-standing adenylation domain involved in the nonribosomal-like biosynthesis of free 4-chlorothreonine in Streptomyces sp. OH-5093. Thr1 shows two monomers in the crystallographic asymmetric unit with different relative orientations of the C- and N-terminal subdomains both in the presence of substrates and in the unliganded form. Co-crystallization with substrates, ATP and L-threonine, yielded one monomer containing the two substrates and the other in complex with L-threonine adenylate, locked in a post-adenylation state. Steady-state kinetics showed that Thr1 activates L-Thr and its stereoisomers, as well as D-Ala, L- and D-Ser, albeit with lower efficiency. Modeling of these substrates in the active site highlighted the molecular bases of substrate discrimination. This work provides the first crystal structure of a threonine-activating adenylation enzyme, a contribution to the studies on conformational rearrangement in adenylation domains and on substrate recognition in nonribosomal biosynthesis