Schistosome invasion of human skin and degradation of dermal elastin are mediated by a single serine protease

Aquatic larvae (cercariae) of the trematode parasite Schistosoma mansoni ra pidly penetrate human skin by degrading host proteins including elastin, Tw o serine proteases, one chymotrypsin-like and the second trypsin-like, have been proposed to be involved. To evaluate the relative roles of these two proteases in larval invasion, both were purified, identified by sequence, a nd then biochemically characterized. The trypsin-like activity was resolved into two distinct serine proteases 76% similar in predicted amino acid seq uence, Southern blot analysis, genomic polymerase chain reaction, and immun olocalization demonstrated that the trypsin-like proteases are in fact not from the schistosome, but are released with larvae from the snail host Biom phalaria glabrata, Invasion inhibition assays using selective inhibitors co nfirmed that the chymotrypsin-like protease is the enzyme involved in skin penetration. Its ability to degrade skin elastin was confirmed, and the thr ee sites of cleavage within elastin help define a new family of elastases.