CHARACTERIZATION AND SUGAR-BINDING PROPERTIES OF ARCELIN-1, AN INSECTICIDAL LECTIN-LIKE PROTEIN ISOLATED FROM KIDNEY BEAN (PHASEOLUS-VULGARIS L. CV RAZ-2) SEEDS

Arcelin-1 is a lectin-like protein found in the seeds of wild varietie s of the kidney bean (Phaseolus vulgaris). This protein displays insec ticidal properties, but the mechanism of action is as yet unknown. In the present study we investigated the biochemical and biophysical prop erties of arcelin-1 from Phaseolus vulgaris cv. RAZ-2. Native arcelin- 1 is a dimeric glycoprotein of 60 kDa, built from the non-covalent ass ociation of two identical monomers. This dimer resists dissociation by chaotropic agents and is highly resistant to proteolytic enzymes. Eac h subunit contains 10% (w/w) neutral sugars which belong to the high-m annose and complex-type glycans attached to three glycosylation sites. No interaction of the protein with simple sugars could be detected, b ut arcelin-1 displays an intrinsic specificity in binding complex glyc ans. Arcelin-1 therefore differs from the closely related phytohaemagg lutinin lectins and alpha-amylase inhibitor in several respects: oligo merization states, sugar-binding affinities and the type and number of glycan chains. These features may be related to the toxicity of arcel in-1.