title: Structure and mechanism of CTP:phosphocholine cytidylyltransferase (LicC) from Streptococcus pneumoniae.
abstract: 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.
authors.affiliation: Department of Structural Biology and the Protein Science Division, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
authors.forename: Bo-Yeon
authors.initials: BY
authors.lastname: Kwak
authors.forename: Yong-Mei
authors.initials: YM
authors.lastname: Zhang
authors.forename: Mikyung
authors.initials: M
authors.lastname: Yun
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Heath
authors.forename: Charles O
authors.initials: CO
authors.lastname: Rock
authors.forename: Suzanne
authors.initials: S
authors.lastname: Jackowski
authors.forename: Hee-Won
authors.initials: HW
authors.lastname: Park
mesh_terms: D002384:Catalysis; D019916:Choline-Phosphate Cytidylyltransferase / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D008958:Models, Molecular; D011487:Protein Conformation; D055672:Static Electricity; D013296:Streptococcus pneumoniae / Q000201:enzymology*; D013379:Substrate Specificity
chemical_list: D019916:Choline-Phosphate Cytidylyltransferase; D008274:Magnesium