INHIBITION OF THE TREHALOSE-P SYNTHASE OF MYCOBACTERIA BY VARIOUS ANTIBIOTICS

A number of antibiotics were tested as potential inhibitors of the pur ified trehalose-P synthase of Mycobacterium smegma-fis. Of about 30 co mpounds tested, 4 (cathomycin, circulin, diumycin, and moenomycin) wer e active against this enzyme. Thus each of these compounds inhibited t he formation of trehalose-P by the purified trehalose-P synthase when either UDP-glucose or GDP-glucose was used as the glucosyl donor. Howe ver, preincubation of the synthase with heparin, a polyanion activator of the enzyme when UDP-glucose is used as the substrate, prevented th e inhibition by these various antibiotics. Fifty percent inhibition by diumycin and moenomycin occurred at a concentration of about 50 mu g/ ml (K-i of about 1 x 10(-5) M), but 50% inhibition by cathomycin and c irculin required substantially higher concentrations (about 50 to 200 mu g/ml), The inhibition by cathomycin, diumycin, and moenomycin was o f the competitive type, whereas that by circulin was noncompetitive in nature. However, the inhibition was of a complex nature and the data suggest two different binding sites for these inhibitors. Photoaffinit y labeling of the synthase with an azido-UDP-[P-32]glucose probe was e ffectively blocked by diumycin, moenomycin, or cathomycin indicating t hat these inhibitors do interact at the substrate binding site. These antibiotics also inhibited the growth of M. smegmatis when added to ce lls innoculated into trypticase soy broth. The inhibition of growth wa s concentration-dependent and directly proportional to the size of the bacterial innoculum. These antibiotics, however, did not inhibit prot ein synthesis nor did they inhibit the incorporation of mannose into l ipid-linked saccharides. (C) 1996 Academic Press, Inc.