The contribution of metal ions to the conformational stability of ribonuclease T-1 - Crystal versus solution

In the crystalline state, ribonuclease T-1 binds calcium ions at different lattice-dependent positions. In solution, its conformational stability is a lso remarkably increased in the presence of divalent metal ions. Combining urea unfolding studies and X-ray crystallography, we compared the presence of several metal ions at specific sites in the protein to their contributio n to the overall stabilizing effect in solution. We constructed thermodynam ic cycles involving particular metal ions and specific carboxylate function s. The resulting coupling energies indicate that some (but not all) metal i ons found at lattice contacts in crystal structures may indeed significantl y contribute to stability enhancement in the presence of metal ions in solu tion.