SMALL-ANGLE X-RAY-SCATTERING AND CRYSTALLOGRAPHIC STUDIES OF ARCELIN-1 - AN INSECTICIDAL LECTIN-LIKE GLYCOPROTEIN FROM PHASEOLUS-VULGARIS L

Arcelin-1 and alpha-amylase inhibitor are two lectin-like glycoprotein s expressed in the seeds of the kidney bean (Phaseolus vulgaris). They display insecticidal activities and protect the seeds from predation by larvae of various bruchids through different biological actions, So lution-state investigations by small-angle X-ray scattering (SAXS) sho w the dimeric structure of arcelin-1, a requirement for its hemaggluti nating properties. Anions were found to have specific properties in th eir effectiveness to disrupt protein aggregates, affect solubility, an d improve crystallizability. The SAXS results were used to improve cry stallization conditions, and single crystals diffracting beyond 1.9 An gstrom resolution were obtained, X-ray diffraction data analysis shows that noncrystallographic symmetry-related arcelin-1 molecules form a lectin-like dimer and reveals the presence of a solvent-exposed anion binding site on the protein, at a crystal-packing interface. The solut ion state properties of arcelin-1 and crystal twinning may be explaine d by the anion specificity of this binding site. (C) 1997 Wiley-Liss, Inc.