title: Structure-based functional annotation: yeast ymr099c codes for a D-hexose-6-phosphate mutarotase.
abstract: Despite the generation of a large amount of sequence information over the last decade, more than 40% of well characterized enzymatic functions still lack associated protein sequences. Assigning protein sequences to documented biochemical functions is an interesting challenge. We illustrate here that structural genomics may be a reasonable approach in addressing these questions. We present the crystal structure of the Saccharomyces cerevisiae YMR099cp, a protein of unknown function. YMR099cp adopts the same fold as galactose mutarotase and shares the same catalytic machinery necessary for the interconversion of the alpha and beta anomers of galactose. The structure revealed the presence in the active site of a sulfate ion attached by an arginine clamp made by the side chain from two strictly conserved arginine residues. This sulfate is ideally positioned to mimic the phosphate group of hexose 6-phosphate. We have subsequently successfully demonstrated that YMR099cp is a hexose-6-phosphate mutarotase with broad substrate specificity. We solved high resolution structures of some substrate enzyme complexes, further confirming our functional hypothesis. The metabolic role of a hexose-6-phosphate mutarotase is discussed. This work illustrates that structural information has been crucial to assign YMR099cp to the orphan EC activity: hexose-phosphate mutarotase.
authors.affiliation: Institut de Biochimie et de Biophysique Moléculaire et Cellulaire, Université Paris-Sud, IFR115, CNRS UMR8619, F-91405 Orsay Cedex, France.
authors.forename: Marc
authors.initials: M
authors.lastname: Graille
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Baltaze
authors.forename: Nicolas
authors.initials: N
authors.lastname: Leulliot
authors.forename: Dominique
authors.initials: D
authors.lastname: Liger
authors.forename: Sophie
authors.initials: S
authors.lastname: Quevillon-Cheruel
authors.forename: Herman
authors.initials: H
authors.lastname: van Tilbeurgh
mesh_terms: D000595:Amino Acid Sequence; D002238:Carbohydrate Epimerases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D006600:Hexosephosphates / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D017510:Protein Folding; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D013329:Structure-Activity Relationship; D013379:Substrate Specificity / Q000235:genetics
chemical_list: D006600:Hexosephosphates; D029701:Saccharomyces cerevisiae Proteins; D002238:Carbohydrate Epimerases; C514950:YMR099c protein, S cerevisiae; C459183:galactose mutarotase