D-ARABITOL METABOLISM IN CANDIDA-ALBICANS - STUDIES OF THE BIOSYNTHETIC-PATHWAY AND THE GENE THAT ENCODES NAD-DEPENDENT D-ARABITOL DEHYDROGENASE

Candida albicans produces large amounts of the pentitol D-arabitol in culture and in infected mammalian hosts, but the functional and pathog enic significance of D-arabitol in C albicans is not known. In this st udy, we sought to elucidate the pathway by which C albicans synthesize s D-arabitol and to identify and characterize key enzymes in this path way. C. albicans B311 produced D-[C-14-1]arabitol from [C-14-2]glucose ; this finding implies on structural grounds that D-ribulose-5-PO4 fro m the pentose pathway is the major metabolic precursor of D-arabitol. NAD- or NADP-dependent pentitol dehydrogenases catalyze the final step s in D-arabitol biosynthesis in other fungi; therefore, lysates of C a lbicans B311 were tested for enzymes of this class and were found to c ontain a previously unknown NAD-dependent D-arabitol dehydrogenase (Ar DH). The ArDH structural gene was cloned by constructing a new D-arabi tol utilization pathway in Escherichia coli. The C albicans ArDH gene expressed in E. coli and Saccharomyces cerevisiae an enzyme that catal yzes the reaction D-arabitol + NAD half arrow right over half arrow le ft D-ribulose + NADH; this gene was present as a single copy per haplo id genome, and its deduced peptide sequence was homologous with sequen ces of several members of the short-chain dehydrogenase family of enzy mes. These results suggest that (i) C albicans synthesizes D-arabitol by dephosphorylating and reducing the pentose pathway intermediate D-r ibulose-5-PO4 and (ii) ArDH catalyzes the final step in this pathway.