PRIMARY STRUCTURE OF A CYSTEINE PROTEINASE-INHIBITOR FROM THE FRUIT OF AVOCADO (PERSEN-AMERICANA MILL)

The complete amino acid sequence of a proteinaceous cysteine proteinas e inhibitor from the fruit of avocado (avocado cystatin) is presented. The protein consists of 100 amino acid residues and has a molecular m ass of 11,300 Da. Comparison of this sequence with sequences of plant cysteine proteinase inhibitors (phytocystatins), including oryzacystat ins I and II from rice seeds, cowpea cystatin, and corn cystatin, shel ved that the avocado cystatin molecule has 60% and 54% residues identi cal 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, amo ng several of the animal cystatins as well as phytocystatins, is at po sitions 47-51 in the avocado cystatin molecule.