CONFORMATIONAL-CHANGES UPON DISSOCIATION OF A GLOBULAR PROTEIN FROM PEA - A FOURIER-TRANSFORM INFRARED-SPECTROSCOPY STUDY

Fourier transform infrared spectroscopy shows that the secondary struc ture of legumin, a globular protein from pea seeds, is composed of 41% beta-sheets and 16% alpha-helices and furthermore reveals the presenc e of beta-turns. The conformation prediction from the analysis of the amino-acid sequence of legumin using hydrophobic cluster analysis reve als that the C-terminal part of the alpha-polypeptide is devoided of d efined secondary structures, whereas the beta-polypeptide is highly or dered. Comparison with analogous 11S globulins from other plant famili es indicates that ordered domains are highly preserved, phenomenon tha t may be associated with the similarity of the quaternary structure of these proteins. The results also reveal the presence of a large hyper variable region, located at the surface of the protein, that could be at the origin of the different functional properties of the 11S type g lobulins. The step-by-step destruction of the quaternary oligomeric st ructure of the native protein is accompanied by conformational changes that depend on the dissociation conditions. Whereas acylation leads t o a decrease of the a-helix content by 10% at the expense of the beta- sheet content, addition of sodium perchlorate results in the conversio n of 10% of the protein secondary structure from beta-sheet to unorder ed. These observations provide further evidence of the existence of di fferent monomeric states that differ from their secondary structure an d, therefore, exhibit different surface-active properties.