THE SOLUTION STRUCTURE OF CONCANAVALIN-A PROBED BY FT-IR SPECTROSCOPY

The secondary structural properties of various forms of concanavalin A in solution were investigated by Fourier-transform infrared spectroscopy in the Amide I region. As in the crystal, the solution structure of the native protein consists mainly of antiparallel .beta.-sheet. Carbohydrate binding does not produce major changes in the overall secondary structure of concanavlin A, but affects infrared bands dure to loops and .beta.-turns. Upon demetallization, the spectrum of concanavalin A shows only a small change in the Amide I band, indicating that whereas the .beta.-sheet structure is conserved, the tertiary properties may be altered. There are also changes in the bands from the tyrosine residue which are compatible with local changes in structure. Confirming tertiary structural differences, the cation-depleted apoprotein is much less stable, denaturing around 63.degree.C, while the native protein denatures only at temperatures around 85.degree.C. Tetramerization proceeds without significant secondary structural change. However, aggregation of the tetramers leads to a significant decrease of the bands corresponding to .beta.-sheet structure, and changes in the tyrosine bands.