Linked Life Data

12180990

Source:http://linkedlifedata.com/resource/pubmed/id/12180990

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
16
pubmed:dateCreated
2002-8-15
pubmed:abstractText
Flavonols are produced by the desaturation of flavanols catalyzed by flavonol synthase. The enzyme belongs to the class of intermolecular dioxygenases which depend on molecular oxygen and FeII/2-oxoglutarate for activity, and have been in focus of structural studies recently. Flavonol synthase cDNAs were cloned from six plant species, but none of the enzymes had been studied in detail. Therefore, a cDNA from Citrus unshiu (Satsuma mandarin) designated as flavonol synthase was expressed in Escherichia coli, and the purified recombinant enzyme was subjected to kinetic and mutational chacterizations. The integrity of the recombinant synthase was revealed by a molecular ion from MALDI-TOF mass spectrometry at m/z 37888 +/- 40 (as compared to 37899 Da calculated for the translated polypeptide), and by partial N-terminal sequencing. Maximal flavonol synthase activity was observed in the range of pH 5-6 with dihydroquercetin as substrate and a temperature optimum at about 37 degrees C. Km values of 272, 11 and 36 micro m were determined for dihydroquercetin, FeII and 2-oxoglutarate, respectively, with a sixfold higher affinity to dihydrokaempferol (Km 45 micro m). Flavonol synthase polypeptides share an overall sequence similarity of 85% (47% identity), whereas only 30-60% similarity were apparent with other dioxygenases. Like the other dioxygenases of this class, Citrus flavonol synthase cDNA encodes eight strictly conserved amino-acid residues which include two histidines (His221, His277) and one acidic amino acid (Asp223) residue for FeII-coordination, an arginine (Arg287) proposed to bind 2-oxoglutarate, and four amino acids (Gly68, His75, Gly261, Pro207) with no obvious functionality. Replacements of Gly68 and Gly261 by alanine reduced the catalytic activity by 95%, while the exchange of these Gly residues for proline completely abolished the enzyme activity. Alternatively, the substitution of Pro207 by glycine hardly affected the activity. The data suggest that Gly68 and Gly261, at least, are required for proper folding of the flavonol synthase polypeptide.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Aug
pubmed:issn
0014-2956
pubmed:author
pubmed:issnType
Print
pubmed:volume
269
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
4134-42
pubmed:dateRevised
2007-7-23
pubmed:meshHeading
pubmed-meshheading:12180990-Amino Acid Sequence, pubmed-meshheading:12180990-Amino Acid Substitution, pubmed-meshheading:12180990-Catalysis, pubmed-meshheading:12180990-Circular Dichroism, pubmed-meshheading:12180990-Citrus, pubmed-meshheading:12180990-DNA, Complementary, pubmed-meshheading:12180990-DNA, Plant, pubmed-meshheading:12180990-Enzyme Induction, pubmed-meshheading:12180990-Flavonoids, pubmed-meshheading:12180990-Flavonols, pubmed-meshheading:12180990-Hydrogen-Ion Concentration, pubmed-meshheading:12180990-Molecular Sequence Data, pubmed-meshheading:12180990-Mutagenesis, Site-Directed, pubmed-meshheading:12180990-Oxidoreductases, pubmed-meshheading:12180990-Plant Proteins, pubmed-meshheading:12180990-Quercetin, pubmed-meshheading:12180990-Recombinant Fusion Proteins, pubmed-meshheading:12180990-Sequence Alignment, pubmed-meshheading:12180990-Sequence Analysis, Protein, pubmed-meshheading:12180990-Sequence Homology, Amino Acid, pubmed-meshheading:12180990-Spectrometry, Mass, Matrix-Assisted Laser..., pubmed-meshheading:12180990-Temperature
pubmed:year
2002
pubmed:articleTitle
Functional expression and mutational analysis of flavonol synthase from Citrus unshiu.
pubmed:affiliation
Institut für Pharmazeutische Biologie, Philipps-Universität Marburg, Germany.
pubmed:publicationType
Journal Article, Comparative Study, Research Support, Non-U.S. Gov't