The inhibitor and NAD are presented as sticks. Analysis of LadA M70F and Y318F Using site directed mutagenesis, specific mutants of LadA were produced in which M70 and Y318 were altered, individually
and in combination, to phenylalanine that is present at these positions in xylitol and D-sorbitol dehydrogenases. The AZD2014 order mutant and the wild type enzymes were expressed in E. coli and purified. Comparison of the kinetic properties www.selleckchem.com/products/XL880(GSK1363089,EXEL-2880).html of wild type LadA and the Y318F mutant protein demonstrated that the Y318F mutant protein had a higher Vmax on L-arabitol and xylitol, but similar affinity (Km) (Table 2). In contrast, the Vmax on D-sorbitol was similar for LadA and the Y318F mutant protein, but the Km of the mutant was nearly 5-times lower (Table 2). Table 2 Kinetic analysis of wild type and mutant LadA Wild type Y318F Km Vmax Kcat Km Vmax Kcat L-arabitol 0.056 96.2 863 0.078 176.8 1800 Xylitol 0.250 131.5 1180 0.218 216.8 2208 D-sorbitol 4.122 90.2 809 0.868 81.8 833 ND = not determined. Discussion Comparison of the deduced amino acid sequences of LadA and XdhA to other L-arabitol, xylitol
and D-sorbitol dehydrogenases, as well as some putative dehydrogenases with unknown function demonstrated that these enzymes form distinct groups in the family of dehydrogenases containing selleckchem an Alcohol dehydrogenase GroES-like domain (pfam08240). Previously it was suggested that L-arabitol dehydrogenase might be the fungal orthologue of D-sorbitol dehydrogenase of higher eukaryotes . find more However, the data in our study indicates that LAD, XDH and SDH are three distinct
families, possibly originating from a common ancestor. Based on sequence identity (data not shown) and enzyme activity XDH appears to be more similar to SDH than LAD, as XDH but not LAD was shown to have significant activity on D-sorbitol , while SDH is significantly more active on xylitol than on L-arabitol (our study). Interestingly, our study suggests that there is no clear fungal orthologue of SDH, based on BLAST and KEGG analysis. As the expression of A. niger ladA and xdhA appears highly specific for L-arabinose and D-xylose , it is unlikely that these enzymes are also acting as a sorbitol dehydrogenase for this fungus. A possible candidate sorbitol dehydrogenase might be the enzyme encoded by the uncharacterised gene from A. niger (An09g03900) that is in the groups that splits of the XDH branch in the tree. As orthologues for this gene were found in all tested fungi, it appears to encode a conserved function. However, bootstrap support for similarity of these enzymes to SDH is weak, indicating that no reliable prediction of function is possible based on these results. The two homologues of LadA described for A. nidulans  cluster in the tree with LadA, but appear as separate branches.