Protein stabilization by compatible solutes

Heteronuclear NMR relaxation measurements and hydrogen exchange data have been used to characterize protein dynamics in the presence or absence of stabilizing solutes from hyperthermophiles. Rubredoxin from Desulfovibrio gigas was selected as a model protein and the effect of diglycerol phosphate on its dynamic behaviour was studied. The presence of 100 mM diglycerol phosphate induces a fourfold increase in the half-life for thermal denaturation of D. gigas rubredoxin [Lamosa, P., Burke, A., Peist, R., Huber, R., Liu, M.Y., Silva, G., Rodrigues-Pousada, C., LeGall, J., Maycock, C. & Santos, H. (2000) Appl. Environ. Microbiol. 66, 1974–1979]. A model-free analysis of the protein backbone relaxation parameters shows an average increase of generalized order parameters of 0.015 reflecting a small overall reduction in mobility of fast-scale motions. Hydrogen exchange data acquired over a temperature span of 20 C yielded thermodynamic parameters for the structural opening reactions that allow for the exchange. This shows that the closed form of the protein is stabilized by an additional 1.6 kJÆmol in the presence of the solute. The results seem to indicate that the stabilizing effect is due mainly to a reduction in mobility of the slower, larger-scale motions within the protein structure with an associated increase in the enthalpy of interactions.