3HL4

Crystal structure of a mammalian CTP:phosphocholine cytidylyltransferase with CDP-choline

Summary for 3HL4

• Entry DOI: 10.2210/pdb3hl4/pdb
• Descriptor: Choline-phosphate cytidylyltransferase A, [2-CYTIDYLATE-O'-PHOSPHONYLOXYL]-ETHYL-TRIMETHYL-AMMONIUM, GLYCEROL, ... (5 entities in total)
• Functional Keywords: cytidylyltransferase, rossmann fold, phospholipid synthesis, phosphatidylcholine, phosphocholine, ctp, cdp-choline, amphitropic protein, lipid metabolism, nucleotidyltransferase, phosphoprotein, transferase
• Biological source: Rattus norvegicus (rat)
• Cellular location: Cytoplasm, cytosol: P19836
• Total number of polymer chains: 2
• Total formula weight: 54975.05

Authors

Lee, J.,Paetzel, M.,Cornell, R.B. (deposition date: 2009-05-26, release date: 2009-09-22, Last modification date: 2024-02-21)

Primary citation

Lee, J.,Johnson, J.E.,Ding, Z.,Paetzel, M.,Cornell, R.B.
Crystal Structure of a mammalian CTP: Phosphocholine cytidylyltransferase catalytic domain reveals novel active site residues within a highly conserved nucleotidyl-transferase fold
J.Biol.Chem., 284:33535-33548, 2009

PubMed Abstract: CTP:phosphocholine cytidylyltransferase (CCT) is the key regulatory enzyme in the synthesis of phosphatidylcholine, the most abundant phospholipid in eukaryotic cell membranes. The CCT-catalyzed transfer of a cytidylyl group from CTP to phosphocholine to form CDP-choline is regulated by a membrane lipid-dependent mechanism imparted by its C-terminal membrane binding domain. We present the first analysis of a crystal structure of a eukaryotic CCT. A deletion construct of rat CCTalpha spanning residues 1-236 (CCT236) lacks the regulatory domain and as a result displays constitutive activity. The 2.2-A structure reveals a CCT236 homodimer in complex with the reaction product, CDP-choline. Each chain is composed of a complete catalytic domain with an intimately associated N-terminal extension, which together with the catalytic domain contributes to the dimer interface. Although the CCT236 structure reveals elements involved in binding cytidine that are conserved with other members of the cytidylyltransferase superfamily, it also features nonconserved active site residues, His-168 and Tyr-173, that make key interactions with the beta-phosphate of CDP-choline. Mutagenesis and kinetic analyses confirmed their role in phosphocholine binding and catalysis. These results demonstrate structural and mechanistic differences in a broadly conserved protein fold across the cytidylyltransferase family. Comparison of the CCT236 structure with those of other nucleotidyltransferases provides evidence for substrate-induced active site loop movements and a disorder-to-order transition of a loop element in the catalytic mechanism.

PubMed: 19783652
DOI: 10.1074/jbc.M109.053363

Experimental method

X-RAY DIFFRACTION (2.2 Å)