Heme binding by proteins and protein-protein complexation are the processes strongly related to the biological activity of proteins. The mechanism of these processes has not been still recognised. These phenomena are presented using haemoglobin as the example. Half of the mature haemoglobin (one α-chain and one β-chain) treated as a dissociation step in haemoglobin degradation reveals a specific change in heme binding after dissociation. This phenomenon is the object of analysis that interprets the structure of both complexes (tetramer and dimer) with respect to their hydrophobic core structure. The results suggest the higher stability of the complex in the form of one α-chain and one β-chain with respect to the hydrophobic core.
The problem of structural similarity of polypeptide chains of low sequence similarity representing a similar 3D structural form has been the object of analysis of researchers engaged in the protein folding problem. Three homologous proteins of similar biological function with low sequence similarity are the objects of analysis presented in this paper. The structure of a hydrophobic core is used as the criterion for structural similarity assessment of these three proteins. The applied method allows recognition of differentiati on in topologically similar structures.
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Four different protein families (two proteinase inhibitor families, myoglobins and lysozymes) were surveyed for correlated mutations with respect to the position distance and their significance in structure stabilization and biological activity. They were chosen for this study in order to verify the currently admitted model of mutational correlation relationship with respect to spatial contact of the residues and contribution in protein biological activity. There was observed high contribution of spatially dispersed residues (which are also not involved in the protein active center) in mutational correlation. Because of the significantly large distance between correlated positions these cases do not correspond explicitly to any mechanism included in current hypotheses. It is suggested that the role of residue spatial contact in structure preservation, intermolecular interaction and active site rescue mechanisms only partially explains the correlation phenomenon.
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