PHOTOAFFINITY ANALOG OF THE SEMISYNTHETIC ECHINOCANDIN LY303366 - IDENTIFICATION OF ECHINOCANDIN TARGETS IN CANDIDA-ALBICANS

The echinocandins are a family of cyclic lipopeptides with potent anti fungal activity. These compounds inhibit the synthesis of beta-1,3-glu can in fungi. The new semisynthetic echinocandin LY303366 was derivati zed to produce a photoactivatable cross-linking echinocandin analog wi th antifungal activity. This analog was radioiodinated and used as a p robe in microsomal membrane preparations of Candida albicans which con tain glucan synthase activity. The photoaffinity probe identified two major proteins of 40 and 18 kDa in both membrane preparations. Labelin g of these proteins was specific in that it required irradiation with UV light and was effectively competed against with unlabeled echinocan din analogs. In addition, the abilities of echinocandin analogs to com pete with the photoaffinity probe correlated to their relative antifun gal potencies and glucan synthase inhibition. The 40-kDa protein was i solated, and partial sequences were obtained from internal peptide fra gments of the protein. Analysis of the sequences of these internal pep tides of the 40-kDa protein revealed that it was a new protein not pre viously described as being involved in glucan synthesis or the mode of action of echinocandins.