Biosynthesis of a novel nucleoside: are two cofactors better than one?

The natural product oxetanocin is a potent antiviral compound produced by Bacillus megaterium NK84-0128. The biosynthesis of oxetanocin has been linked to a plasmid-borne gene cluster that contains four genes involved in oxetanocin production (oxsA and oxsB) and oxetanocin resistance (oxrA and oxrB). In collaboration with the Liu Lab at the University of Texas, Austin, we now present detailed structural and biochemical analysis that confirms the involvement of the cobalamin (Cbl) dependent S-adenosylmethionine (AdoMet) radical enzyme, OxsB, and an HD-domain phosphohydrolase enzyme, OxsA, in oxetanocin production. These studies of OxsB provide a framework for understanding the coordination and interplay of AdoMet and Cbl cofactors in performing Nature’s chemistry. Additional X-ray crystal structures of the oxetanocin production partner protein, OxsA, reveal a phosphohydrolase enzyme with a restructured active site specific for a phosphorylated oxetanocin derivative. Our crystallographic endeavors and sequence-based comparisons have allowed for elucidation of a biochemical scheme for the challenging production of oxetanocin, expanded the catalytic repertoire of the HD-domain phosphohydrolase enzyme superfamily, and provided the first structural characterization of a Cbl-dependent AdoMet radical enzyme.
Jennifer Bridwell-Rabb (Massachusetts Institute of Technology)