Interaction of L-glutamate oxidase with triazine dyes: selection of ligands for affinity chromatography.
Glutamate oxidase (GOX, EC 1.4.3.11) from Streptomyces catalyses the oxidation of L-glutamate to alpha-ketoglutarate. Its kinetic constants for L-glutamate were measured equal to 2 mM for Km and 85.8 s(-1) for kcat. BLAST search and amino acid sequence alignments revealed low homology to other L-amino acid oxidases (18-38%). Threading methodology, homology modeling and CASTp analysis resulted in certain conclusions concerning the structure of catalytic alpha-subunit and led to the prediction of a binding pocket that provides favorable conditions of accommodating negatively charged aromatic ligands, such as sulphonated triazine dyes. Eleven commercial textile dyes and four biomimetic dyes or minodyes, bearing a ketocarboxylated-structure as their terminal biomimetic moiety, immobilized on cross-linked agarose gel. The resulted mini-library of affinity adsorbents was screened for binding and eluting L-glutamate oxidase activity. All but Cibacron Blue 3GA (CB3GA) affinity adsorbents were able to bind GOX at pH 5.6. One immobilized minodye-ligand, bearing as its terminal biomimetic moiety p-aminobenzyloxanylic acid (BM1), displayed the higher affinity for GOX. Kinetic inhibition studies showed that BM1 inhibits GOX in a non-competitive manner with a Ki of 10.5 microM, indicating that the dye-enzyme interaction does not involve the substrate-binding site. Adsorption equilibrium data, obtained from a batch system with BM1 adsorbent, corresponded well to the Freundlich isotherm with a rate constant k of 2.7 mg(1/2)ml(1/2)/g and Freundlich isotherm exponent n of 1. The interaction of GOX with the BM1 adsorbent was further studied with regards to adsorption and elution conditions. The results obtained were exploited in the development of a facile purification protocol for GOX, which led to 335-fold purification in a single step with high enzyme recovery (95%). The present purification procedure is the most efficient reported so far for L-glutamate oxidase.
Katsos
N E
NE
Laboratory of Enzyme Technology, Department of Agricultural Biotechnology, Agricultural University of Athens, 75 Iera Odos Street, GR-11855 Athens, Greece.
Labrou
N E
NE
Clonis
Y D
YD
D000327:Adsorption; D000594:Amino Acid Oxidoreductases / Q000737:chemistry*; D000595:Amino Acid Sequence; D000818:Animals; D002846:Chromatography, Affinity / Q000379:methods*; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D014227:Triazines / Q000737:chemistry*
D008024:Ligands; D014227:Triazines; D000594:Amino Acid Oxidoreductases; C023061:L-glutamate oxidase