3tw3
From Proteopedia
Crystal structure of RtcA.ATP.Co ternary complex
Structural highlights
Function[RTCA_ECOLI] Catalyzes the conversion of 3'-phosphate to a 2',3'-cyclic phosphodiester at the end of RNA. The mechanism of action of the enzyme occurs in 3 steps: (A) adenylation of the enzyme by ATP; (B) transfer of adenylate to an RNA-N3'P to produce RNA-N3'PP5'A; (C) and attack of the adjacent 2'-hydroxyl on the 3'-phosphorus in the diester linkage to produce the cyclic end product. The biological role of this enzyme is unknown but it is likely to function in some aspects of cellular RNA processing.[1] Publication Abstract from PubMedRNA 3'-phosphate cyclase (RtcA) synthesizes RNA 2',3' cyclic phosphate ends via three steps: reaction with ATP to form a covalent RtcA-(histidinyl-Nepsilon)-AMP intermediate; transfer of adenylate to an RNA 3'-phosphate to form RNA(3')pp(5')A; and attack of the vicinal O2' on the 3'-phosphorus to form a 2',3' cyclic phosphate and release AMP. Here we report the crystal structures of RtcA*ATP, RtcA*ATP*Mn(2+), and RtcA*ATP*Co(2+) substrate complexes and an RtcA*AMP product complex. Together with the structures of RtcA apoenzyme and the covalent RtcA-AMP intermediate, they illuminate the mechanism of nucleotidyl transfer, especially the stereochemical transitions at the AMP phosphate, the critical role of the metal in orienting the PP(i) leaving group of ATP during step 1, and the protein conformational switches that accompany substrate binding and product release. The octahedral metal complex of RtcA*ATP*Mn(2+) includes nonbridging oxygens from each of the ATP phosphates, two waters, and Glu14 as the sole RtcA component. Whereas the RtcA adenylylation step is metal-catalyzed, the subsequent steps in the cyclization pathway are metal-independent. Structures of RNA 3'-phosphate cyclase bound to ATP reveal the mechanism of nucleotidyl transfer and metal-assisted catalysis.,Chakravarty AK, Smith P, Shuman S Proc Natl Acad Sci U S A. 2011 Dec 13. PMID:22167800[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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