[Local structure of cytochrome c from horse heart in solution. Conformational analysis using data of two-dimensional nuclear Overhauser effect spectroscopy].

The research paper involves the analysis of the different shapes (conformations) of horse heart cytochrome c in both its oxidized and reduced states, using the data obtained from two-dimensional nuclear Overhauser effect spectroscopy. It found that the secondary structures of both forms of the protein were similar, but slight differences existed in parts of the protein chain located near the heme crevice.

Methodology and Findings

• The investigation used a method earlier suggested for calculating the backbone conformations of the horse heart cytochrome c. This was performed using two-dimensional nuclear Overhauser effect spectroscopy data.
• The structural elements of both the oxidized (ferricytochrome c) and reduced (ferrocytochrome c) forms of the protein were revealed in this process.
• The team also worked on revealing and analyzing the conformations of non-regular, irregular polypeptide chain segments within the protein.
• The study found a noticeable similarity in the secondary structures of both ferri- and ferrocytochrome c forms when they were in solution. This was established from the comparison of their conformations.
• Nevertheless, some minor differences were found between the conformations. These differences were localized within the polypeptide chain fragments that lay in the vicinity of the heme crevice.

Comparison and Further Analysis

• Further comparisons were made of the dihedral phi and psi angles in the calculated conformations of horse cytochrome C versus the corresponding characteristics of X-ray structures of tuna ferri- and ferrocytochrome c. Both oxidized and reduced forms of the protein were considered in this comparison, using quantitative criteria.
• The comparisons suggested that there was a similarity between the conformations as seen in solution and crystal forms.
• The study demonstrated that the conformational changes of individual amino acid residues resulting from the “solution-to-crystal” transition took place on the surface fragments of the protein globule. However, these changes did not significantly alter the secondary structure of the molecule.