THE ALPHA-MANNOSIDASE OF TRYPANOSOMA-CRUZI - STRUCTURE AND FUNCTION

Trypanosoma cruzi alpha-mannosidase has been purified to apparent homo geneity. It is a 240,000-Da tetramer composed of four identical subuni ts (58,000 Da). Each subunit contains one N-linked high-mannose oligos accharide. Based on pH optimum and sensitivity to inhibition by swains onine, we suggest it to be lysosomal, but this has yet to be demonstra ted directly. The enzyme appears to be developmentally regulated and m ay be a key enzyme in the degradation of the lipopeptidophosphoglycan (LPPG) during transformation from epimastigote to trypomastigote. Prel iminary experiments suggest T. cruzi does not utilize the mannose 6-ph osphate recognition system for sorting a-mannosidase (or other acid hy drolases) to the lysosome. To clone the a-mannosidase from T. cruzi we have used the same approach that has been used for other alpha-mannos idases. The cDNA amplification product was subcloned and sequenced. Co mparison of the T. cruzi alpha-mannosidase sequence with the alpha-man nosidases that were used in the original primer design demonstrated a greater similarity to murine lysosomal and Dictyostelium alpha-mannosi dases than to Golgi alpha-mannosidases.