-arabinose catabolism. The final two reactions of the fungal L-arabinose pathway are shared with the D-xylose catabolic pathway (Figure 1). The bacterial isomerase pathway consists of an L-arabinose isomerase, ribulokinase, and L-ribulose phosphate-4-epimerase, whilst the enzyme sequence of the oxidative pathway consists of L-arabinose dehydrogenase, L-arabinolactonase, L-arabonate dehydratase, L-2-keto-3-deoxy-arabonate dehydratase, and 2,52013 American Chemical SocietyPdioxovalerate dehydrogenase, the end solution getting ketoglutarate. In a modification of this oxidative pathway, L-2keto-3-deoxy-arabonate is split by an aldolase into pyruvate and glycoaldehyde.7,8 Most of the genes and proteins involved in the fungal L-arabinose pathway have been characterized within the two ascomycetes Aspergillus niger and Trichoderma reesei.four In T. reesei L-arabinose reduction is mediated by the NADPH distinct D-xylose reductase XYL1, that is the significant reductase activity for the reduction of both pentoses D-xylose and L-arabinose.9,ten In a. niger, this NADPH-dependent reduction is accomplished by an L-arabinose distinct LarA as well as a D-xylose particular XyrA.Ceritinib 11 The subsequent steps are mediated by L-arabitol 4-dehydrogenase,12,13 L-xylulose reductase,14 xylitol dehydrogenase,15 and xylulose kinase.Baicalein 16 Enzymes with L-xylulose reductase activity are located within the quick chain dehydrogenase and reductase family17 and take part in the glucuronic acid/uronate cycle of mammals.PMID:23415682 In humans, LXR deficiency causes pentosuria, a clinically benign condition that final results in big amounts of L-xylulose in the urine of such patients.18 The initial fungal L-xylulose reductase, ALX1, was identified inside the yeast Ambrosiozyma monospora and, interestingly, is NADH-dependent.19 Despite the fact that an enzyme with 20 L-xylulose reductase (LXR1) was described for T. reesei, its functional characterization showed that it is truly a DReceived: November 26, 2012 Revised: March 16, 2013 Published: March 18,dx.doi.org/10.1021/bi301583u | Biochemistry 2013, 52, 2453-BiochemistryArticleFigure 1. Fungal L-arabinose degrading pathway represented by enzymes of A. niger and T. reesei. The initial three distinct methods of the fungal L-arabinose catabolism lead to xylitol, the very first frequent intermediate from the L-arabinose and D-xylose pathway. Xylitol is then converted to D-xylulose 5-phosphate before getting into the pentose phosphate pathway. L-Arabinose reduction is mainly mediated by the D-xylose reductase XYL1 in T. reesei, while A. niger features a certain Larabinose reductase LarA.mannitol 2-dehydrogenase.21,22 Only lately was a accurate Lxylulose reductase LxrA identified inside a. niger. Its deletion resulted in an pretty much total loss in the NADPH certain Lxylulose reductase activity but had an only little effect around the development on L-arabinose because the carbon source, explained by the presence of a NADH-dependent L-xylulose reductase activity.14 On the other hand, deletion of the LxrA homologue LXR4 in T. reesei showed that this gene will not be involved inside the oxidoreductive catabolism of L-arabinose but of D-galactose.23 To clone putative LXRs involved in L-arabinose catabolism in T. reesei, we made use with the fact that all LXRs identified to date are identified inside the group of short chain dehydrogenases and reductases. Consequently, we screened the T. reesei genome database for SDRs encoding genes and reduced the amount of LXR candidates by selecting for extremely conserved fungal LXRs which might be expressed inside the presence of L-arabinose.
