Cleavage specificity of cucumisin, a serine protease, with synthetic substrates

The substrate specificity of a plant serine protease, cucumisin (EC 3.4.21.25), was studied by the use of synthetic oligopeptides and peptidyl-pNA substrates. Since P1'-Ser, Ala, and Gly substrates were hydrolyzed rapidly, cucumisin appears to prefer a small side chain at the P1' position of the oligopeptide substrate. The k(cat)/K-m for the hydrolysis of P1-Leu, Ala, Phe, and Glu substrates demonstrated that they were preferentially cleaved over P1-Lys, diaminopropionic acid (Dap), Gly, Val, and Pro substrates. From the digestion of peptidyl-pNAs, the specificity of the protease was determined to be broad, but the preferential cleavage sites were hydrophobic amino acid residues at the P1 position. (C) 2000 Elsevier Science Ltd. All rights reserved.