Role of macromolecular crowding and salt ions on the structural-fluctuation of a highly compact configuration of carbonmonoxycytochrome c

Role of Macromolecular Crowding on Stability and Iron Release Kinetics of Serum Transferrin

“…Sectors 1 and 2 correspond to stabilizing cosolutes, while sectors 3 and 4 correspond to destabilizing cosolutes. Furthermore, sectors 1 and 3 represent the enthalpically dominated effect, while sectors 2 and 4 represent entropically dominated effect. , The enthalpy–entropy plots for reductive iron release from Fe N Tf, collected in the absence and presence of 200 mg mL –1 of dextran 40, dextran 70, and ficoll 70 at pH 7.4 and 5.5 lie in sector 1 (Figure e,f), which is in general agreement with the models that describe enthalpically dominated stabilization. , …”

“…The enthalpy–entropy plots for reductive iron release from Fe N Tf, collected in the absence and presence of crowder at pH 7.4 and 5.5, reveal that ,in controlling iron release from Fe N Tf in the presence of crowding agent under physiological and endosomal pH conditions, the enthalpic effect is more dominated than the entropic one (Figure e,f). Previously it was established that crowder-induced protein stabilization through purely steric excluded volume effect is entropic. ,, However, recent studies showed that the observed effect of crowders on protein stability and folding have a significant enthalpic contributions. ,, Moreover enthalpic effect even dominates over entropic contributions. ,, To account for enthalpic as well as entropic effects of crowders, some recent reports suggest that it is necessary to augment the steric excluded volume effects with other nonspecific interactions. ,,,, Therefore, the present study highlights that both hard-core repulsions and nonspecific soft chemical interactions must be considered to understand the effects of crowding agent on the iron release from Fe N Tf under physiological and endosomal pH conditions. Current result suggests that hard and soft interactions are always present, but their relative influences on protein depend on the size, shape, and chemical nature of the crowders.…”

“…To test whether the crowding presence affects the thermodynamic activation parameter for reductive iron release, the Eyring plots for Fe 2+ release reaction of Fe N Tf obtained in the absence and presence of 200 mg mL –1 crowding agent (dextran 40, dextran 70, and ficoll 70) at pH 7.4 (Figure a) and 5.5 (Figure b) were analyzed using eq …”

“…As described earlier, , the enthalpy–entropy plot could be used to determine enthalpic and entropic contributions toward the stability, folding, and dynamics of proteins. The enthalpy–entropy plot has four sectors (Figure e,f).…”

“…Previous reports concluded that crowder environment increases the thermal and structural stability of proteins. ,,− The guanidine hydrochloride (GdnHCl)-induced equilibrium unfolding of native apoazurin revealed that the stabilizing effect of ficoll 70 is less than any of the dextrans (dextran 20, dextran 40, and dextran 70), and among the dextrans no size dependent effect was observed . However, GdnHCl-induced equilibrium unfolding transitions of ferrocytochrome c at pH 7 showed that the smaller sized crowder (dextran 40) has a greater impact on the thermodynamic stability of protein and typically follows the order dextran 40 > dextran 70 > ficoll 70 . The thermal stability of flavodoxin is increased more in the presence of dextran 70 than ficoll 70 .…”