CHARACTERIZATION OF A PHOSPHOLIPASE C-RESISTANT INOSITOL CONTAINING GLYCOLIPID FROM TRYPANOSOMA-CRUZI

Since glycosylphosphatidylinositol is the most common form of attachme nt of proteins to membranes in T. cruzi, and that this parasite depend s on surface-mediated interactions for survival within the vector and mammalian host, it is probable that a drug which interfers with the me tabolism of glycosylphosphatidylinositol (GPI) could be successfully e mployed in chemotherapy. Over the last few years several groups have b een characterizing this mode of attachment in T. cruzi and more recent ly we have been concentrating our efforts on the identification of can didate precursors for protein anchors in metacyclic trypomastigotes. P reviously detected GPI heterogeneity regarding solubilization of a maj or stage-specific antigen (1G7-Ag) by phospholipase C led us to invest igate whether biosynthetic precursors with similar properties could al so be identified. Two glycolipid species whose migration properties re semble glycolipids A and C of T. brucei were amenable to biosynthetic radiolabelling with palmitic acid, inositol, ethanolamine, glucosamine and mannose. Following purification,these species were submitted to c lassical GPI diagnostic treatments. In both cases digestion with GPI-s pecific phospholipase D (GPIPLD) produced phospatidic acid and treatme nt with either mild base or phospholipase A(2) (PLA(2)) produced free fatty acid, indicating an acylation at least at position 2 of the glyc erol. The glycolipid A-like species proved to be susceptible to solubi lization by PIPLC of B. thuringiensis and by GPIPLC of T. brucei and t he glycolipid C-like material proved to be fully resistant to both lip ases. Although the glycolipid A-like species indeed presents these and other properties compatible with a precursor for the chemically chara cterized 1 G7-Ag anchor, the PLC-resistant species which is completely insensitive to nitrous acid deamination might be an exception to the general finding of a non-acetylated glucosamine in the GPI moieties so far described.