A MAJOR SURFACE-ANTIGEN OF PROCYCLIC STAGE TRYPANOSOMA-CONGOLENSE

Five monoclonal antibodies (mAb) were raised that bound to the surface of procyclic stage Trypanosoma congolense with high intensity in immu nofluorescence. Immunoblot analysis of trypanosome lysates using 3 of these mAb revealed a diffuse SDS-PAGE band of 36-40 kDa. The purified antigen did not react with Coomassie Blue or silver stains, but did st ain blue with Stains-all(TM), indicating acidity. For the one mAb test ed, the epitope was periodate-sensitive and therefore probably glycan. Although this antigen shares properties with procyclin/PARP, which fo rms a surface coat on procyclic Trypanosoma brucei, a search in T. con golense for homologues of a procyclin/PARP gene revealed only non-codi ng sequence of partial similarity. Using a differential screen, a proc yclic stage T. congolense cDNA clone was isolated that encoded a putat ive 256-amino acid protein containing 2 peptides chemically sequenced independently by Beecroft et al. [36]. The protein, termed glutamate a nd alanine-rich protein (GARP), has potential hydrophobic leader and t ail sequences (the latter with potential for replacement by a glycosyl phosphoinositol anchor) and no potential N-linked glycosylation sites . It has no significant sequence homology with known proteins. Antibod ies against a translational fusion of GARP bound specifically in Weste rn blots to a band very similar to that detected by the mAb and also t o the purified antigen. Immunogold electron microscopy revealed a dens e packing of the antigen on the cell surface. It appears that procycli c T. brucei and T. congolense have major surface proteins with structu ral analogy, but with no sequence homology.