1jyk
From Proteopedia
Catalytic Mechanism of CTP:phosphocholine Cytidylytransferase from Streptococcus pneumoniae (LicC)
Overview
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.
About this Structure
1JYK is a Single protein structure of sequence from Streptococcus pneumoniae. Full crystallographic information is available from OCA.
Reference
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 Page seeded by OCA on Fri May 2 22:04:52 2008
