Inhibition Mechanism and Molecular Evolution of Amylase- and Protease-Inhibitors

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Based on our previous finding of an extraordinary dicergent evolution that Hordeum uulgare (barley) trypsin inhibitor is structurally related to Triticum (wheat) -amylase inhibitors, Ricinus communis(castor bean) seed strage protein, and mammalian pancreatic secretory trypsin inhibitors, we have investigated the structure-function relationship and molecular evelution of these proteins. Detailed comparison of these inhibitors suggested that they have arisen from fusion of two ancestral genes coding for a proteinase inhibitor and an -amylase inhibitor of about 7 kda in tandem, and subsequent mutation had made one of the inhibitory site silent or specific for some unknown enzymes. This domain structure was partially confirmed by determination of 3 (out of 5) disulfide bridges in the barley inhibitor. It is of particular interest that the potential -amylase inhibitory domain is also homologous to bovine pancreatic secretory trypsin inhibitor (kazal), indicating the unusual dicergent evolut … More ion of a proteinase- and an -amylase-inhibitors from a single ancestral gene.Plant seeds contain a number of low nolecular mass proteins of known and unknown function. We have identified an unusually hydrophobic protein in glycine max (soybean) seeds, and determined the complete primary structure. The protein showed a very weak inhibitory action on mammalian triacylglycerol lipases, and also a weak and partial sequence similarity to the above described proteins and to bowman-birk type inhibitors, which suggest the presence of a protein superfamily including a wide variety of proteins. It also showed a marked and unexpected similarity to a mammalian hormone, rat prolaction. Another unusual protein, soybean aspartic acid-rich polypeptide, has been isolated and sequence. The protein is remarkable for its high content of aspartic acid, and sequence analysis showed that the protein has a long poly(L-aspartic acid) tail at the C-terminus which interacts with trypsin.Post-translational modifications, important for manifestation of protein fonctions, is rather difficult to detect by the ordinary analytical systems. We have constructed a rapid and sensitive detection system for modified amino acids and applied to the present investigation. Less