The larval form of the parasite Schistosomamansoni infects humans by first penetrating the skin and then invading through the connective tissues. To invade through the connective tissue, the larvae secrete an enzyme that catalyzes the cleavage of peptide bonds between residues X and Y in the sequence -Gly-Pro-X-Y- (X and Y can be any of several amino acids). What is this enzyme and why is this enzyme activity important for the parasite to invade the connective tissue?