title: GTP cyclohydrolase II structure and mechanism.
abstract: GTP cyclohydrolase II converts GTP to 2,5-diamino-6-beta-ribosyl-4(3H)-pyrimidinone 5'-phosphate, formate and pyrophosphate, the first step in riboflavin biosynthesis. The essential role of riboflavin in metabolism and the absence of GTP cyclohydrolase II in higher eukaryotes makes it a potential novel selective antimicrobial drug target. GTP cyclohydrolase II catalyzes a distinctive overall reaction from GTP cyclohydrolase I; the latter converts GTP to dihydroneopterin triphosphate, utilized in folate and tetrahydrobiopterin biosynthesis. The structure of GTP cyclohydrolase II determined at 1.54-A resolution reveals both a different protein fold to GTP cyclohydrolase I and distinctive molecular recognition determinants for GTP; although in both enzymes there is a bound catalytic zinc. The GTP cyclohydrolase II.GMPCPP complex structure shows Arg(128) interacting with the alpha-phosphonate, and thus in the case of GTP, Arg(128) is positioned to act as the nucleophile for pyrophosphate release and formation of the proposed covalent guanylyl-GTP cyclohydrolase II intermediate. Tyr(105) is identified as playing a key role in GTP ring opening; it is hydrogen-bonded to the zinc-activated water molecule, the latter being positioned for nucleophilic attack on the guanine C-8 atom. Although GTP cyclohydrolase I and GTP cyclohydrolase II both use a zinc ion for the GTP ring opening and formate release, different residues are utilized in each case to catalyze this reaction step.
authors.affiliation: Division of Structural Biology, The Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford, OX3 7BN, United Kingdom.
authors.forename: Jingshan
authors.initials: J
authors.lastname: Ren
authors.forename: Masayo
authors.initials: M
authors.lastname: Kotaka
authors.forename: Michael
authors.initials: M
authors.lastname: Lockyer
authors.forename: Heather K
authors.initials: HK
authors.lastname: Lamb
authors.forename: Alastair R
authors.initials: AR
authors.lastname: Hawkins
authors.forename: David K
authors.initials: DK
authors.lastname: Stammers
mesh_terms: D001665:Binding Sites; D003460:Crystallization; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D006136:GTP Cyclohydrolase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D015394:Molecular Structure; D011487:Protein Conformation; D014443:Tyrosine / Q000378:metabolism; D015032:Zinc / Q000378:metabolism
chemical_list: D014443:Tyrosine; C004805:5'-guanylylmethylenebisphosphonate; D006160:Guanosine Triphosphate; D006136:GTP Cyclohydrolase; D015032:Zinc