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Title: Activation of bean (Phaseolus vulgaris) [alpha]-amylase inhibitor requires proteolytic processing of the proprotein

Seeds of the common bean (Phaseolus vulgaris) contain a plant defense protein that inhibits the [alpha]-amylases of mammals and insects. This [alpha]-amylase inhibitor ([alpha]Al) is synthesized as a proprotein on the endoplasmic reticulum and is proteolytically processed after arrival in the protein storage vacuoles to polypeptides of relative molecular weight (M[sub r]) 15,000 to 18,000. The authors report two types of evidence that proteolytic processing is linked to activation of the inhibitory activity. First, by surveying seed extracts of wild accessions of P. vulgaris and other species in the genus Phaseolus, they found that antibodies to [alpha]Al recognize large (M[sub r] 30,000-35,000) polypeptides as well as typical [alpha]Al processing products (M[sub r] 15,000-18,000). [alpha]Al activity was found in all extracts that had the typical [alpha]Al processed polypeptides, but was absent from seed extracts that lacked such polypeptides. Second, they made a mutant [alpha]Al in which asparagine-77 is changed to aspartic acid-77. This mutation slows down the proteolytic processing of pro-[alpha]Al when the gene is expressed in tobacco. When pro-[alpha]Al was separated from mature [alpha]Al by gel filtration, pro-[alpha]Al was found not to have [alpha]-amylase inhibitory activity. The authors interpret these results to mean that formation of the active inhibitor ismore » causally related to proteolytic processing of the proprotein. They suggest that the polypeptide cleavage removes a conformation constraint on the precursor to produce the biochemically active molecule. 43 refs., 5 figs., 1 tab.« less
Authors:
; ;  [1]
  1. (Univ. of California, San Diego, La Jolla (United States))
Publication Date:
OSTI Identifier:
6448805
Resource Type:
Journal Article
Resource Relation:
Journal Name: Plant Physiology; (United States); Journal Volume: 101:4
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; AMYLASE; INHIBITION; BIOCHEMISTRY; PLANTS; RESPONSE MODIFYING FACTORS; ASPARAGINE; ASPARTIC ACID; BIOLOGICAL PATHWAYS; ENDOPLASMIC RETICULUM; INSECTS; MAMMALS; PHASEOLUS; POLYPEPTIDES; PRECURSOR; PROTEINS; PROTEOLYSIS; SEEDS; TOBACCO; AMIDES; AMINO ACIDS; ANIMALS; ARTHROPODS; CARBOXYLIC ACIDS; CELL CONSTITUENTS; CHEMICAL REACTIONS; CHEMISTRY; DECOMPOSITION; ENZYMES; GLYCOSYL HYDROLASES; HYDROLASES; INVERTEBRATES; LEGUMINOSAE; MAGNOLIOPHYTA; MAGNOLIOPSIDA; O-GLYCOSYL HYDROLASES; ORGANIC ACIDS; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; PEPTIDES; VERTEBRATES 550200* -- Biochemistry