Proteasomes are molecular machines found in virtually all cells that provide one of the mechanisms
for protein turnover. We have analysed the 20S proteasome of Schistosoma mansoni, the
first multimeric complex isolated from this helminth parasite. Three chromatographic steps
were employed to yield a highly homogeneous preparation. 2-DE of the purified complex
revealed 58 spots, of which 46 could be assigned either an a or a b proteasome signature by MS.
Most of the 14 transcripts (7a and 7b) encoded by the parasite genome were represented by
multiple spots and we suggest that this diversity is due to PTMs of subunits. For most of the
isoforms, variations in pI predominated although alterations in mass were also observed. 2-DE
separations of extracts from infective cercariae and blood-dwelling adult worms probed by
Western blotting, using a human anti-a subunit antibody, revealed different patterns of reactivity,
most probably in a3 and a6 subunits, on the basis of sequence conservation. This difference was
rapidly lost following transformation of the cercaria to the skin schistosomulum stage, suggesting
that changes in the proteasome structure, likely caused by the introduction of a new set of
PTMs, precede remodelling of the parasite body prior to intravascular migration