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Publication Abstract from PubMed

Pneumococcal LicC is a member of the nucleoside triphosphate transferase superfamily and catalyzes the transfer of a cytidine monophosphate from CTP to phosphocholine to form CDP-choline. The structures of apo-LicC and the LicC-CDP-choline-Mg(2+) ternary complex were determined, and the comparison of these structures reveals a significant conformational change driven by the multivalent coordination of Mg(2+). The key event is breaking the Glu(216)-Arg(129) salt bridge, which triggers the coalescence of four individual beta-strands into two extended beta-sheets. These movements reorient the side chains of Trp(136) and Tyr(190) for the optimal binding and alignment of the phosphocholine moiety. Consistent with these conformational changes, LicC operates via a compulsory ordered kinetic mechanism. The structures explain the substrate specificity of LicC for CTP and phosphocholine and implicate a direct role for Mg(2+) in aligning phosphocholine for in-line nucleophilic attack and stabilizing the negative charge that develops in the pentacoordinate transition state. These results provide a structural basis for assigning a specific role for magnesium in the catalytic mechanism of pneumococcal LicC.

Structure and mechanism of CTP:phosphocholine cytidylyltransferase (LicC) from Streptococcus pneumoniae.,Kwak BY, Zhang YM, Yun M, Heath RJ, Rock CO, Jackowski S, Park HW J Biol Chem. 2002 Feb 8;277(6):4343-50. Epub 2001 Nov 12. PMID:11706035^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.