A NOVEL ALPHA-AMYLASE INHIBITOR FROM AMARANTH (AMARANTHUS-HYPOCONDRIACUS) SEEDS

The major alpha-amylase inhibitor (AAT) present in the seeds of Amaran thus hypocondriacus, a variety of the Mexican crop plant amaranth, is a 32-residue-long polypeptide with three disulfide bridges. Purified A AI strongly inhibits the alpha-amylase activity of insect larvae (Trib olium castaneum and Prostephanus truncatus) and does not inhibit prote ases and mammalian alpha-amylases. AAI was sequenced with the automate d Edman method, and the disulfide bridges were localized using enzymat ic and chemical fragmentation methods combined with N-terminal sequenc ing. AAI is the shortest alpha-amylase inhibitor described so far whic h has no known close homologs in the sequence data bases. Its residue conservation patterns and disulfide connectivity are related to the sq uash family of proteinase inhibitors, to the cellulose binding domain of cellobiohydrolase, and to omega-conotoxin, i.e. a group of small pr oteins termed ''knottins'' by Nguyen, D. L., Heitz, A., Chiche, L., Ca stro, B., Boigegrain, R., Favel, A., and Coletti-Previero, M. ((1990) (Biochimie 72, 431-435) The three-dimensional model of AAI was built a ccording to the common structural features of this group of proteins u sing side chain replacement and molecular dynamics refinement techniqu es.