Conformation of concanavalin A and its fragments in aqueous solution and organic solvent-water mixtures

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Abstract
The conformations of concanavalin A (con A), an all-β protein, and its three CNBr-cleaved fragments were studied by CD. Con A in buffer showed a 197 nm maximum and a 223 nm minimum, which were red-shifted by 6–7 nm from those of regular all-β proteins and β-sheet of (Lys) n . Fragment 1 (residue 1–42) resembled an unordered form with a CD maximum at 200 nm, but fragments 2 (residues 43–129) and 3 (residues 130–237) showed a regular CD spectrum with two extrema at 192–193 nm (+) and 214–216 nm (−). Equimolar mixture of the three fragments showed some degree of interaction, but did not reconstitute the conformation of native con A, probably because of the loss of bound Ca2+ and Mn2+ ions in the fragments. In ethanol-, methanol-, and dioxane-water mixed solvents, con A and its fragments remained as β-sheet. In contrast, addition of trifluoroethanol and sodium dodecyl sulfate induceda-helix at the expense of β-sheet for con A and its fragments in aqueous solution. In 80% trifluoroethanol, the induced helicities exceeded their sequence-predicted helix-potentials, but in 10 mM sodium dodecyl sulfate the helicities agreed well with corresponding predictions.