期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2016
卷号：113
期号：48
页码：13750-13755
DOI：10.1073/pnas.1613610113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceOver the past few decades, natural products, or chemical compounds derived from plants, animals, or microbes have greatly inspired drug discovery. Because natural products often have more complex and architecturally unique scaffolds than available man-made drugs, characterization of natural product biosynthetic pathways often reveals unprecedented chemistry and enzymatic platforms. Oxetanocin-A (OXT) is a natural product nucleoside analog that has an unusual four-membered oxetane ring connected to an adenine base. Prior to this work, there were no details available about OXT biosynthesis. Here, we not only elucidate a scheme for the two-enzyme catalyzed production of OXT, but also reveal modifications to an HD domain phosphohydrolase enzyme scaffold that expand the catalytic repertoire of this enzyme superfamily. HD domain phosphohydrolase enzymes are characterized by a conserved set of histidine and aspartate residues that coordinate an active site metallocenter. Despite the important roles these enzymes play in nucleotide metabolism and signal transduction, few have been both biochemically and structurally characterized. Here, we present X-ray crystal structures and biochemical characterization of the Bacillus megaterium HD domain phosphohydrolase OxsA, involved in the biosynthesis of the antitumor, antiviral, and antibacterial compound oxetanocin-A. These studies reveal a previously uncharacterized reaction for this family; OxsA catalyzes the conversion of a triphosphorylated compound into a nucleoside, releasing one molecule of inorganic phosphate at a time. Remarkably, this functionality is a result of the OxsA active site, which based on structural and kinetic analyses has been tailored to bind the small, four-membered ring of oxetanocin-A over larger substrates. Furthermore, our OxsA structures show an active site that switches from a dinuclear to a mononuclear metal center as phosphates are eliminated from substrate.
