The pentose catabolic pathway has been studied mainly in Aspergillus niger, Aspergillus nidulans and Trichoderma reesei (Hypocrea jecorina) and, except for L-arabinose reductase and L-xylulose reductase, all genes from the pathway have been identified and characterised
[2–11]. In vitro Temsirolimus cell line analysis of the substrate specificity of A. niger L-arabitol dehydrogenase and xylitol dehydrogenase demonstrated that L-arabitol dehydrogenase is active on L-arabitol and xylitol, but not on D-sorbitol, while xylitol dehydrogenase is active on xylitol and D-sorbitol, but not on L-arabitol [5]. In this study we aimed to elucidate the structural basis for the differences in substrate specificity particularly concerning the activity on D-sorbitol. Results Fungal xylitol see more and L-arabitol dehydrogenases form separate groups from D-sorbitol dehydrogenases of higher eukaryotes in the family of dehydrogenases containing a Alcohol dehydrogenase GroES-like domain (pfam08240) To determine whether fungal genomes contain homologues of D-sorbitol dehydrogenases MK-0457 manufacturer of higher eukaryotes, the human D-sorbitol dehydrogenase [12] amino acid sequence was blasted against the genomes of A. niger, A. nidulans and A. oryzae at the comparative Aspergillus server from the Broad Institute http://www.broad.mit.edu/annotation/genome/aspergillus_group/MultiHome.html.
However, the highest hit for these fungi was xylitol dehydrogenase (data not shown). In addition, the KEGG website http://www.genome.ad.jp/dbget-bin/www_bget?enzyme+1.1.1.15 was searched for putative D-sorbitol dehydrogenases of A. niger. Two of these DCLK1 corresponded to ladA and xdhA, while a third was An09g03900. In addition,
two homologues of A. nidulans ladA, ladB and ladC, have been described [7] although no biochemical function has been reported for these proteins. Putative orthologues for ladB were only found in A. niger and A. oryzae, while orthologues for ladC were only absent in N. crassa and T. reeseii out of the 8 fungi tested in this study. To determine the phylogenetic relationships between L-arabitol dehydrogenases, xylitol dehydrogenases and D-sorbitol dehydrogenases, an alignment was performed using amino acid sequences of established and putative L-arabitol and xylitol dehydrogenases of eight fungi, D-sorbitol dehydrogenases of ten eukaryotes and the other genes found in the analysis described above. A bootstrapped NJ tree (1000 bootstraps, Fig. 1) of the alignment shows that the D-sorbitol dehydrogenases of animals and plants split into two groups reflecting the kingdoms. The fungal L-arabitol and xylitol dehydrogenases form separate groups in the tree. In addition, a group with unknown function that contains the additional A. niger gene found in the KEGG database splits of from the xylitol dehydrogenase branch, although this clade only has a low bootstrap support (50%).