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  • Title: Crystal structure of a bifunctional transformylase and cyclohydrolase enzyme in purine biosynthesis.
    Author: Greasley SE, Horton P, Ramcharan J, Beardsley GP, Benkovic SJ, Wilson IA.
    Journal: Nat Struct Biol; 2001 May; 8(5):402-6. PubMed ID: 11323713.
    Abstract:
    ATIC, the product of the purH gene, is a 64 kDa bifunctional enzyme that possesses the final two activities in de novo purine biosynthesis, AICAR transformylase and IMP cyclohydrolase. The crystal structure of avian ATIC has been determined to 1.75 A resolution by the MAD method using a Se-methionine modified enzyme. ATIC forms an intertwined dimer with an extensive interface of approximately 5,000 A(2) per monomer. Each monomer is composed of two novel, separate functional domains. The N-terminal domain (up to residue 199) is responsible for the IMPCH activity, whereas the AICAR Tfase activity resides in the C-terminal domain (200-593). The active sites of the IMPCH and AICAR Tfase domains are approximately 50 A apart, with no structural evidence of a tunnel connecting the two active sites. The crystal structure of ATIC provides a framework to probe both catalytic mechanisms and to design specific inhibitors for use in cancer chemotherapy and inflammation.
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