Efficient and selective isotopic labeling of hemes to facilitate the study of multiheme proteins

Specific isotopic labeling of hemes provides a unique opportunity to characterize the structure and function of heme-proteins. Unfortunately, current methods do not allow efficient labeling in high yields of multiheme cytochromes c, which are of great biotechnological interest. Here, a method for production of recombinant multiheme cytochromes c in Escherichia coli with isotopically labeled hemes is reported. A small tetraheme cytochrome of 12 kDa from Shewanella oneidensis MR-1 was used to demonstrate the method, achieving a production of 4 mg pure protein per liter. This method achieves, in a single step, efficient expression and incorporation of hemes isotopically labeled in specific atom positions adequate for spectroscopic characterization of these complex heme proteins. It is, furthermore, of general application to heme proteins, opening new possibilities for the characterization of this important class of proteins.