Novo Heme Proteins

Two reports in 1994 began to develop the concepts of coordination chemistry based self-assembly of heme into designed protein scaffolds. In collaborative work, the laboratories of DeGrado and Dutton provided two related architectures for de novo heme protein design... 

The heme moiety provides de novo designed heme proteins with an intrinsic and spectroscopically rich probe. The interaction of the amide bonds of the peptide or protein with the heme macrocycle provides for an induced circular dichroism spectrum indicative of protein-cofactor interactions. The strong optical properties of the heme macrocycle also make it suitable for resonance Raman spectroscopy. Aside from the heme macrocycle, the encapsulated metal ion itself provides a spectroscopic probe into its electronic structure via EPR spectroscopy and electrochemistry. These spectroscopic and electrochemical tools provide a strong quantitative base for the detailed evaluation of the relative successes of de novo heme proteins. 

The rich spectroscopy and electrochemistry of the heme moiety yields a wealth of opportunities for the denovo heme protein design to evaluate the success of the heme binding site design. Combinations of these spectroscopic and electrochemical methods are elucidating the structure and function of de novo heme proteins and illustrating that they serve as excellent bioinorganic model complexes for simple cytochromes. 

Figure 8 Template approach to de novo heme protein design using metalloporphyrins as templates, (a) helichrome (b) tetraphilins (c) artificial membrane proteins. (Reprinted with permission from Ref. 22. 2001 the American Chemical Society) (d) helical proteins based on Cys-containing cyclic peptide. (Reprinted with permission from H.K. Ran, N. DeJonge, and W. Haehnel, Proc. Natl. Acad. Sci. U.S.A., 1998, 95, 11526. 1998 National Academy of Sciences, USA)...

Figure 9 Self assembly approach to de novo heme protein design, (a) bis-His ligated single heme parallel to the helices in the four a-helical bundle (b) bis-His ligated multi-hemes parallel to the helices in the four a-helical bundle. (Reprinted with permission from Ref 27. 2004 the American Chemical Society) (c) bis-His ligated multi-hemes perpendicular to each other in the four a-helical bundle. (Reprinted with permission from Ref 60. 2001 the Protein Society)...

Novel peroxidases can be generated by screening de novo heme-proteins derived from a designed combinatorial library. Turnover numbers as high as 17,000 min have been obtained. 

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