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| - Identification of Catalytic Amino Acids in the Human GTP FucosePyrophosphorylase Active Site
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| - GTP-l-fucose pyrophosphorylase(GFPP) catalyzes the reversible formation of the nucleotide-sugar GDP-β-l-fucose from guanosine triphosphate and β-l-fucose-1-phosphate. The enzyme functionsprimarily in the mammalian liver and kidney to salvage free fucose during the breakdown of glycoproteinsand glycolipids. GFPP shares little primary sequence identity with other nucleotide-sugar metabolizingenzymes, and the three-dimensional structure of the protein is unknown. The enzyme does contain severalsequences that could be nucleotide binding sites, but none of them are an exact match to consensussequences. Using a combination of site-directed mutagenesis and UV photoaffinity cross-linking, we haveidentified five amino acid residues that are critical for catalysis. Some of these amino acids are foundwithin the poorly conserved nucleotide binding consensus structures, while others represent new motifs.Two active site lysines can be cross-linked to photoaffinity probes. The site of cross-linking depends onthe probe used. The identification of these critical residues highlights how distinct GFPP is from othernucleotide-sugar pyrophosphorylases.
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