Isolation and Partial Characterization of Three Proteinsynthesis Inhibitory Proteins from the Seeds of Luffa cylindrica

Abstract

Three new proteins which inhibit protein synthesis in rabbit reticulocyte lysates were isolated from an extract of sponge gourd (Luffa cylindrica) seeds by chromatography on a AF-Blue Toyopearl column followed by FPLC with a Mono S column. These three protein-synthesis inhibitory proteins (PSIs) have molecular masses of 19kDa, 15kDa, and 9kDa, and were designated 19K-PSI, 15K-PSI, and 9K-PSI, respectively. Although the 19K-PSI had no effect on protein synthesis in HeLa cells, its inhibitory activity on the cell-free protein synthesis was 340- and 83-fold stronger than those of ricin A-chain and luffin-a, respectively, probably due to hydrolyzing mRNA. The inhibitory activities of 15Kand 9K-PSIs on the cell-free protein synthesis were weaker than those of ricin A-chain and luffin-a. The 19K-PSI was a glycoprotein having an ordinary amino acid composition, three intramolecular disulfide bonds and a blocked N-terminal residue, while the 15K-PSI was extraordinarily rich in glycine and the 9K-PSI in arginine and glutamic acid (and/or glutamine). The amino acid composition of 19K-PSI was: Ser₂₇Glx₃Gly₁₆₄Tyr₇Lys₉His₆, and that of 9K-PSI was: Asx₃Glx₂₅Pro₂Gly₅Lys₂His₂Arg₂₅Trp₃.