Histone proteins are not only important due to their vital role in cellular processes such as DNA compaction, replication and repair but also show intriguing structural properties that might be exploited for bioengineering purposes such as the development of nano-materials. Based on their biological and technological implications, it is interesting to investigate the structural properties of proteins as a function of temperature. In this work, we study the spatial response dynamics of the histone H2AX, consisting of 143 residues, by a coarse-grained bond fluctuating model for a broad range of normalized temperatures. A knowledge-based interaction matrix is used as input for the residue-residue Lennard-Jones potential.
We find a variety of equilibrium structures including global globular configurations at low normalized temperature ( ), combination of segmental globules and elongated chains ( ), predominantly elongated chains ( ), as well as universal SAW conformations at high normalized temperature ( ). The radius of gyration of the protein exhibits a non-monotonic temperature dependence with a maximum at a characteristic temperature ( ) where a crossover occurs from a positive (stretching at ) to negative (contraction at ) thermal response on increasing .