A CALORIMETRIC STUDY OF THE EFFECTS OF GLN(16)-LEU AND TYR(26)-ASP AMINO-ACID SUBSTITUTIONS ON THE STRUCTURE AND STABILITY OF THE CRO REPRESSOR OF PHAGE-LAMBDA
Vb. Rogov et Yv. Griko, A CALORIMETRIC STUDY OF THE EFFECTS OF GLN(16)-LEU AND TYR(26)-ASP AMINO-ACID SUBSTITUTIONS ON THE STRUCTURE AND STABILITY OF THE CRO REPRESSOR OF PHAGE-LAMBDA, Molecular biology, 27(4), 1993, pp. 488-491
The effects of amino acid substitutions on the thermodynamic parameter
s of the cooperative molecular structure formation and stabilization i
n the phage lambda Cro repressor were investigated by scanning calorim
etry. Gln(16)-Leu and Tyr(26)-Asp substitutions were found to increase
protein stability by 32 degrees C relative to the wild-type protein.
The values of the denaturation enthalpy for the wild-type and variant
Cro protein, as measured calorimetrically at the same temperature, dif
fer insignificantly, while the apparent enthalpy is considerably small
er for the variant protein. An analysis of the excess heat capacity of
the variant protein indicated that this composite parameter measured
experimentally can be approximated by a combination of two functions,
suggesting the occurrence of two pseudoindependent transitions. The st
abilization and redistribution of intramolecular interactions in the r
epressor molecule caused by the substitutions result thus in splitting
the unified cooperative molecular system into two interacting domains
. A plausible mechanism of the domain structure formation is discussed
on the basis of the calorimetric evidence obtained.