Structural highlights
Publication Abstract from PubMedClostridium thermocellum polynucleotide kinase (CthPnk), the 5' end-healing module of a bacterial RNA repair system, catalyzes reversible phosphoryl transfer from an NTP donor to a 5'-OH polynucleotide acceptor. Here we report the crystal structures of CthPnk-D38N in a Michaelis complex with GTP*Mg2+ and a 5'-OH oligonucleotide and a product complex with GDP*Mg2+ and a 5'-PO4 oligonucleotide. The O5' nucleophile is situated 3.0 A from the GTP gamma phosphorus in the Michaelis complex, where it is coordinated by Asn38 and is apical to the bridging beta phosphate oxygen of the GDP leaving group. In the product complex, the transferred phosphate has undergone stereochemical inversion and Asn38 coordinates the 5'-bridging phosphate oxygen of the oligonucleotide. The D38N enzyme is poised for catalysis, but cannot execute because it lacks Asp38-hereby implicated as the essential general base catalyst that abstracts a proton from the 5'-OH during the kinase reaction. Asp38 serves as a general acid catalyst during the 'reverse kinase' reaction by donating a proton to the O5' leaving group of the 5'-PO4 strand. The acceptor strand binding mode of CthPnk is distinct from that of bacteriophage T4 Pnk. Structures of bacterial polynucleotide kinase in a Michaelis complex with GTP*Mg2+ and 5'-OH oligonucleotide and a product complex with GDP*Mg2+ and 5'-PO4 oligonucleotide reveal a mechanism of general acid-base catalysis and the determinants of phosphoacceptor recognition.,Das U, Wang LK, Smith P, Jacewicz A, Shuman S Nucleic Acids Res. 2013 Oct 22. PMID:24150947[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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