POSITION-120-123, A POTENTIAL ACTIVE-SITE OF TRICHOSANTHIN

Trichosanthin (TCS) is a type-I ribosome-inactivating protein (RIP) wi th wide spectrum of biological and pharmacological activities. In the present study, a potential site on the TCS molecule (position 120-123) is identified which may be important for the biological activities of TCS. By using site-directed mutagenesis, position 120-123 of TCS was either deleted or changed from Lys-Ile-Arg-Glu (hydrophilic) to Ser-Al a-Gly-Gly (hydrophobic). Deletion of these residues rendered a TCS mol ecule completely deprived of ribosome inactivating activity, while hyd rophobic replacement caused 4000-fold decrease in ribosome inactivatin g activity. The abortifacient activity of these two mutants was retain ed with decreased potency. This implies that position 120-123 of the n ative TCS molecule plays a critical role in maintaining its biological activity.