[On the role of some conserved and nonconserved amino acid residues in transition state and in intermediate of apomyoglobin folding].

The effect of some amino acid residues in A, B, G, and H helices on the folding nucleus and folding intermediate state formation was estimated. For four apomyoglobin mutant forms with point replacements of hydrophobic amino acid residues by Ala, the influence of the substitutions on the stability of native (N) protein and its folding intermediate state (I) was studied, as well as on the protein folding/unfolding rates. Equilibrium and kinetic studies on mutant proteins over a wide range of urea concentrations have shown that the protein native state was strongly destabilized in comparison with that of the wild type protein. At the same time, stability of the intermediate state changed insignificantly. It was shown that amino acid residues of A, G, and H helices make a small contribution to apomyoglobin folding nucleus stabilization in the rate-limiting I reversible N transition, which occurred after the intermediate state was formed. But the amino acid residue of B-helix was very important for the folding nucleus stabilization in the transition state upon the I reversible N transition.