Structural Characterization of an α-Amylase Inhibitor from a Wild Common Bean (Phaseolus vulgaris): Insight into the Common Structural Features of Leguminous α-Amylase Inhibitors

抄録

The primary structures of two subunits of an α-amylase inhibitor (αAI-2) from a wild common bean (Phaseolus vulgaris) were revealed by a comparison of the amino acid sequence previusly deduced from the nucleotide sequence with the amino- and carboxyl-terminal amino acid sequences determined by conventional methods. The polypeptide molecular weight of αAI-2 obtained by the light-scattering technique, considered together with the sequence molecular weights revealed for the subunits, indicated that αAI-2 has the subunit stoichiometry of an α₂β₂ complex. These structural features were closely similar to those recently elucidated for a white kidney bean (P. vulgaris) α-amylase inhibitor, which is quite different in the inhibitory specificity from αAI-2. The post-translational processing of the precursor glycoproteins to form the tetrameric structure appeared to require an Arg residue close to the processing site. Further, the proper associations of the subunits into the tetrameric structures seemed to be strictly controlled by a few amino acids on the subunit interfaces.