Two‐stage thermal unfolding of [Cys55]‐substituted Cro repressor of bacteriophage λ

Abstract

It has been shown by scanning calorimetry and ¹H NMR spectroscopy that thermal denaturation of mutant λ phage cro repressor in which Val⁵⁵ was substituted for Cys, proceeds in 2 stages in contrast to the wild type protein. At neutral pH values, an additional cooperative transition has been observed at about 100°C. Calorimetric measurements on the mutant and its tryptic fragment lead to the conclusion that the two-stage character of thermal unfolding of the mutant is due to a disruption of an additional cooperative domain in the dimer molecule which is stabilized by the S–S crosslink.