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

Journal Article · Thu Apr 01 00:00:00 EST 1993 · Plant Physiology; (United States)

DOI:https://doi.org/10.1104/pp.101.4.1341· OSTI ID:6448805

Pueyo, J J; Hunt, D C; Chrispeels, M J ^[1]

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1. Univ. of California, San Diego, La Jolla (United States)

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 is 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.

• OSTI ID: 6448805
• Journal Information: Plant Physiology; (United States), Vol. 101:4; ISSN 0032-0889
• Country of Publication: United States
• Language: English

Related Subjects

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