We are calculating the protein A - protein B complex structure , Binding interface of the complex is validating the by construct the mutants on interface of protein A , Other-side most of the residues are conserved on protein B .
After obtaining the ITC experiments ,the binding interaction between Protein A (wild type) and protein B was driven by the Entropy .But in case of ALA mutation of ASP ( Mutant ) , the binding was driven by the Enthalpy ( Entropy got reduced and change in Enthalpy was negative) . and binding affinity got reduced to 150 time compare to wild type.
Is it possible that entropy driven interaction can turn to enthalpy driven? What could be possible reasons?
I found that some of references which is indicating the similar observations .
One of the publication depend on mutagensis study ( J. Biol. Chem. 2010, 285:20390-20398 ) described Entropy and Enthalpy interconversion as follows :
The binding interfaces can be modulated by changes in residues that affect either the binding enthalpy or the entropy, thus providing additional freedom to maintain an interaction during the course of evolution, this effect that has been described previously as entropy/enthalpy compensation(1,2) .
(1) J. Biol. Chem. 283, 19581–19592
(2) Chem. Biol. 10, 1023–1032
(3) Nature 488, 236–240 (09 August 2012)
The distinction between entropy and enthalpy is certainly convenient in terms of differing chemical interactions which together lead to protein/protein binding. However, in the final analysis -delta H for the binding is heat release into the surroundings and thus an increase in entropy of the4 surroundings. Where delta G is the change in free energy of the binding and delta S(tot) is the total change in entropy (system plus surroundings)
-deltaG = + delta S(tot). So in the long run protein/proteon binding is all entropy driven.
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