Tuna cytochrome c at 2.0 A resolution. I. Ferricytochrome structure analysis

Area of Science:

• Biochemistry
• Structural Biology
• Crystallography

Background:

• Cytochrome c is a vital protein in cellular respiration.
• Previous studies on horse ferricytochrome c suggested a different heme crevice conformation.

Purpose of the Study:

• To determine the high-resolution crystal structure of oxidized tuna cytochrome c.
• To clarify the structural details of the heme crevice and its surrounding residues.

Main Methods:

• X-ray diffraction analysis.
• Crystallization using four isomorphous heavy atom derivatives.
• Structure solution to 2.0 A resolution.

Main Results:

• The crystal structure of oxidized tuna cytochrome c was solved at 2.0 A resolution.
• Two independent cytochrome molecules were observed in the asymmetric unit with minor surface side chain differences.
• The phenylalanine 83 residue was found to close the heme crevice, consistent with the ferrocytochrome c structure.

Conclusions:

• The molecular folding of oxidized tuna cytochrome c is similar to its reduced form.
• The heme crevice is closed by phenylalanine 83, contradicting earlier findings from horse ferricytochrome c.