Structural origins of pH and ionic strength effects on protein stability. Acid denaturation of sperm whale apomyoglobin.

摘要: A recently developed approach to calculate the pH dependence of protein stability from three-dimensional structure information is applied analysis acid denaturation sperm whale apomyoglobin. The finite difference Poisson-Boltzmann method used pKa values and these are obtain titration curves for folded as well compact intermediates. total electrostatic free energy change involved in apomyoglobin unfolding then evaluated. Calculations carried out native (N) intermediate (I) relative unfolded state (U) over a range at various ionic strengths. contributions key ionizable groups process discussed. For acid-induced partial near 5, transition N I found be driven by three histidines that exposed when B, C, D E helices unfold. Similarly, consisting A, G H primarily few carboxylic acids with low state. This picture contrast view which attributes repulsion resulting build up positive charge. In fact, charge-charge interactions myoglobin attractive all where unfolds. pH-dependent changes contribute but other effects, such hydrogen bonding solvation, important well. effect increasing strength on attributed decrease destabilize I, stabilize U reducing shifts critical acids. more stable than neutral thus accounting its presence an folding pathway. Our results have implications origins intermediates or "molten globule" states.