Inositol phosphoryl transferases from human pathogenic fungi.

The IPC1 gene from Saccharomyces cerevisiae, which encodes inositolphosphorylceramide (IPC) synthase, was first identified as a novel and essential gene encoding resistance to the natural product antifungal aureobasidin A (AUR1). The formation of IPC in fungi is essential for viability, suggesting inhibitors of IPC1p function would make ideal antifungal drug candidates. Homologs of the AUR1/IPC1 gene were identified from a number of human pathogenic fungi, Candida glabrata, Candida krusei, Candida parapsilosis, Candida tropicalis and Cryptococcus neoformans. Comparison of these genes with other homologous genes from Candida albicans, Aspergillus fumigatus, Aspergillus nidulans, Saccharomyces cerevisiae and Schizosaccharomyces pombe reveals a conserved structural motif for inositolphosphoryl transferases which is similar to a motif recently described for lipid phosphatases, but with unique characteristics.

Photoaffinity analog of the semisynthetic echinocandin LY303366: identification of echinocandin targets in Candida albicans.

The echinocandins are a family of cyclic lipopeptides with potent antifungal activity. These compounds inhibit the synthesis of BETA-1,3-glucan in fungi. The new semisynthetic echinocandin LY303366 was derivatized to produce a photoactivatable cross-linking echinocandin analog with antifungal activity. This analog was radioiodinated and used as a probe in microsomal membrane preparations of Candida albicans which contain glucan synthase activity. The photoaffinity probe identified two major proteins of 40 and 18 kDa in both membrane preparations. Labeling of these proteins was specific in that it required irradiation with UV light and was effectively competed against with unlabeled echinocandin analogs. In addition, the abilities of echinocandin analogs to compete with the photoaffinity probe correlated to their relative antifungal potencies and glucan synthase inhibition. The 40-kDa protein was isolated, and partial sequences were obtained from internal peptide fragments of the protein. Analysis of the sequences of these internal peptides of the 40-kDa protein revealed that it was a new protein not previously described as being involved in glucan synthesis or the mode of action of echinocandins.

The AUR1 gene in Saccharomyces cerevisiae encodes dominant resistance to the antifungal agent aureobasidin A (LY295337).

Aureobasidin A (LY295337) is a cyclic depsipeptide antifungal agent with activity against Candida spp. The mechanism of action of LY295337 remains unknown. LY295337 also shows activity against the yeast Saccharomyces cerevisiae. Generation of a mutant of S. cerevisiae resistant to LY295337 is reported. Resistance was found to reside in a dominant mutation of a single gene which has been named AUR1 (aureobasidin resistance). This gene was cloned and sequenced. A search for homologous sequences in GenBank and by BLAST did not elucidate the function of this gene, although sequence homology too an open reading frame from the Saccharomyces genome sequencing project and several other adjacent loci was noted. Deletion of aur1 was accomplished in a diploid S. cerevisiae strain. Subsequent sporulation and dissection of the aur1/aur1 delta diploid resulted in tetrads demonstrating 2:2 segregation of viable and nonviable spores, indicating that deletion of aur1 is lethal. As LY295337 is fungicidal and deletion of aur1 is lethal, aur1 represents a potential candidate for the target of LY295337.

Human X-linked phosphoribosylpyrophosphate synthetase superactivity is associated with distinct point mutations in the PRPS1 gene.

Superactivity of phosphoribosylpyrophosphate synthetase (PRS) is an X chromosome-linked disorder of purine metabolism, characterized by gout with uric acid overproduction and, in some families, neurodevelopmental impairment. Two highly homologous isoforms of PRS (PRS1 and PRS2), each encoded by a distinct X chromosome-linked locus, have been identified, and PRS1 and 2 cDNAs have been cloned. The entire 954-base pair translated regions of PRS1 and 2 cDNAs derived from cultured lymphoblasts and fibroblasts from two patients in whom purine nucleotide feedback resistance of PRS is associated with enzyme superactivity and neurodevelopmental defects were examined by direct sequencing after polymerase chain reaction amplification of PRS transcripts. Nucleotide sequences of PRS2 cDNAs from the patients and normal individuals were identical. In contrast, PRS1 cDNAs from the patients differ from normal PRS1 cDNA, each by a single base substitution. PRS1 cDNA from patient N. B. showed an A to G transition at nucleotide 341, corresponding to an asparagine to serine change at amino acid residue 113 of mature PRS1. A G to C transversion at nucleotide 547, indicating an aspartic acid to histidine change at amino acid 182, was found for PRS1 cDNA from patient S. M. Point mutations at the sites identified in the PRS1 cDNAs of the two patients were confirmed by the results of RNase mapping analysis. Normal, N. B., and S. M. PRS1 cDNAs were introduced into Escherichia coli BL21 (DE3)/pLyS, and recombinant N. B. and S. M. PRS1s showed the purine nucleotide feedback resistance phenotypes characteristic of PRS from patients' cells.

Cloning of cDNAs for human phosphoribosylpyrophosphate synthetases 1 and 2 and X chromosome localization of PRPS1 and PRPS2 genes.

Cloned cDNAs representing the entire, homologous (80%) translated sequences of human phosphoribosylpyrophosphate synthetase (PRS) 1 and PRS 2 cDNAs were utilized as probes to localize the corresponding human PRPS1 and PRPS2 genes, previously reported to be X chromosome linked. PRPS1 and PRPS2 loci mapped to the intervals Xq22-q24 and Xp22.2-p22.3, respectively, using a combination of in situ chromosomal hybridization and human x rodent somatic cell panel genomic DNA hybridization analyses. A PRPS1-related gene or pseudogene (PRPS1L2) was also identified using in situ chromosomal hybridization at 9q33-q34. Human HPRT and PRPS1 loci are not closely linked. Despite marked cDNA and deduced amino acid sequence homology, human PRS 1 and PRS 2 isoforms are encoded by genes widely separated on the X chromosome.

Analysis of yeast retrotransposon Ty insertions at the CAN1 locus.

The target site distribution for 55 independent Ty insertions that inactivate the function of the Saccharomyces cerevisiae CAN1 gene is reported. Under some selection conditions Ty elements inserted preferentially into the promoter and exhibited an orientation bias. In contrast, under other conditions no insertions were detected in the promoter region and transposition appeared to occur randomly throughout the CAN1 coding sequence. These results show that the target site distribution for Ty insertions may be a function of the selection conditions.