Effect of cyclodextrins on the thermal stability of globular proteins

摘要: Since unfolding of globular proteins normally involves exposure buried hydrophobic side chains,' the binding cyclodextrins2 to these exposed residues should destabilize native conformations by shifting equilibrium in favor unfolded polypeptide chain. This indeed appears be case. Differential scanning calorimetry (DSC)3 a range shows that a-CD reduces mean temperature (T,,,) for all examined (Figure l ) , and increasing cyclodextrin concentration progressively thermal stability manner consistent with weak non-covalent attachment molecules onto chain 2). On molar basis, is more effective reducing protein than either urea or guanidine hydrochloride under similar condition^,^ although it much less soluble. Alongside this reduction T,,, there decrease transition enthalpy (AH,,,). Part arises from normal dependence AH,,, arising heat capacity effects (ACP).l However, even after correction effect, observed enthalpies are consistently lower expected up 10 kcal mol-' at highest concentrations available. The ACp values themselves also generally presence a-CD, as indicated post-transition base lines 1, except PGK where obscured exothermic aggregation). Both sites on polypeptide. Heats complex formation between aromatic groups small but (-1 -4 mol-'),6 such would both reduce overall and, burying within CD cavity, AC,. A simple model assuming n identical independent shift (AT,,, = Tm0) depend ligand [a-CD] thus: