title: Re-design of Saccharomyces cerevisiae flavocytochrome b2: introduction of L-mandelate dehydrogenase activity.
abstract: Flavocytochrome b2 from Saccharomyces cerevisiae is an l-lactate dehydrogenase which exhibits only barely detectable activity levels towards another 2-hydroxyacid, l-mandelate. Using protein engineering methods we have altered the active site of flavocytochrome b2 and successfully introduced substantial mandelate dehydrogenase activity into the enzyme. Changes to Ala-198 and Leu-230 have significant effects on the ability of the enzyme to utilize l-mandelate as a substrate. The double mutation of Ala-198-->Gly and Leu-230-->Ala results in an enzyme with a kcat value (25 degrees C) with L-mandelate of 8.5 s-1, which represents an increase of greater than 400-fold over the wild-type enzyme. Perhaps more significantly, the mutant enzyme has a catalytic efficiency (as judged by kcat/Km values) that is 6-fold higher with l-mandelate than it is with L-lactate. Closer examination of the X-ray structure of S. cerevisiae flavocytochrome b2 led us to conclude that one of the haem propionate groups might interfere with the binding of L-mandelate at the active site of the enzyme. To test this idea, the activity with l-mandelate of the independently expressed flavodehydrogenase domain (FDH), was examined and found to be higher than that seen with the wild-type enzyme. In addition, the double mutation of Ala-198-->Gly and Leu-230-->Ala introduced into FDH produced the greatest mandelate dehydrogenase activity increase, with a kcat value more than 700-fold greater than that seen with the wild-type holoenzyme. In addition, the enzyme efficiency (kcat/Km) of this mutant enzyme was more than 20-fold greater with L-mandelate than with l-lactate. We have therefore succeeded in constructing an enzyme which is now a better mandelate dehydrogenase than a lactate dehydrogenase.
authors.affiliation: Institute of Cell and Molecular Biology, Department of Chemistry, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JR, Scotland, U.K.
authors.forename: R
authors.initials: R
authors.lastname: Sinclair
authors.forename: G A
authors.initials: GA
authors.lastname: Reid
authors.forename: S K
authors.initials: SK
authors.lastname: Chapman
mesh_terms: D000429:Alcohol Oxidoreductases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D019943:Amino Acid Substitution; D001665:Binding Sites; D018360:Crystallography, X-Ray; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D042844:L-Lactate Dehydrogenase (Cytochrome); D019344:Lactic Acid / Q000378:metabolism; D008333:Mandelic Acids / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013379:Substrate Specificity
chemical_list: D008333:Mandelic Acids; D019344:Lactic Acid; D000429:Alcohol Oxidoreductases; D007770:L-Lactate Dehydrogenase; D042844:L-Lactate Dehydrogenase (Cytochrome); C021538:L-mandelate dehydrogenase; C037938:mandelic acid