Primary Structure of a Cysteine Proteinase Inhibitor from the Fruit of Avocado (Persea americana Mill)

Abstract

The complete amino acid sequence of a proteinaceous cysteine proteinase inhibitor from the fruit of avocado (avocado cystatin)is presented. The protein consists of 100 amino acid residues and has a molecular mass of 11, 300 Da. Comparison of this sequence with sequences of plant cysteine proteinase inhibitors (phytocystatins), including oryzacystatins I and II from rice seeds, cowpea cystatin, and corn cystatin, showed that the avocado cystatin molecule has 60% and 54% residues identical with the two forms of the rice seed proteins, oryzacystatins I and II, respectively, and 64% and 63% with the cowpea and corn proteins, respectively. The totally conserved sequence, Gln-Val-Val-Ala-Gly, among several of the animal cystatins as well as phytocystatins, is at positions 47-51in the avocado cystatin molecule.