Three-dimensional structure of cyanomet-sulfmyoglobin C

Area of Science:

• Biochemistry
• Structural Biology
• X-ray Crystallography

Background:

• Sulfmyoglobin is a stable derivative of myoglobin.
• Myoglobin's prosthetic group, protoheme IX, can be chemically modified.
• Understanding protein-cofactor interactions is crucial in biochemistry.

Purpose of the Study:

• To determine the three-dimensional atomic structure of horse heart cyanomet-sulfmyoglobin C.
• To characterize the structural impact of converting the protoheme IX prosthetic group to an iron-chlorin.
• To investigate the structural consequences of sulfur incorporation into the myoglobin prosthetic group.

Main Methods:

• X-ray crystallography was employed to resolve the protein structure to 2.0 A resolution.
• The protoheme IX prosthetic group was chemically modified to a chlorin.
• Structural analysis focused on the protein's overall conformation and the prosthetic group's environment.

Main Results:

• The atomic structure of horse heart cyanomet-sulfmyoglobin C was successfully elucidated.
• The protoheme IX was converted to a chlorin, featuring a saturated pyrrole ring and an exocyclic thiolene ring.
• The polypeptide chain conformation remained largely similar to the native protein, but the prosthetic group and surrounding residues were distorted due to sulfur incorporation.

Conclusions:

• This study presents the first three-dimensional structure of a protein with an iron-chlorin prosthetic group.
• Sulfur incorporation into the prosthetic group causes significant local distortions within the heme pocket.
• The findings provide valuable insights into the structural adaptability of proteins to modified prosthetic groups.