Iron(III) Protoporphyrin IX Associates with Proteins in a Sequence-Dependent Manner

The role and action of heme as a regulatory effector of proteins came more and more into the focus of biochemical research aiming at a complete understanding of this molecule’s function in the organism apart from its well-investigated embedment in hemoproteins, which e.g. are involved in gas transport, catalytic reactions or electron transfer [1-3]. Transient binding of regulatory heme to proteins might significantly change a protein's function. Distinct sequence stretches on the protein surface are responsible for interaction with heme. As a consequence of association, conformational changes within the protein may lead to changes in the protein's activity [4]. Interactions between heme and characteristic iron-coordinating amino acids (cysteine, histidine, tyrosine) are well-known. In addition, however, the surrounding amino acids contribute to the association of the protein with the protoporphyrin ring system. This fact was confirmed by results of a combinatorial peptide library screening [1]. Based on these data we predicted motifs for heme binding as well as proteins as possible targets, such as dipeptidyl peptidase 8 which subsequently was proven to be inhibited by heme [5]. Further targets possessing a great potential as heme-regulated proteins are currently under investigation. In-depth structural studies e.g. using UV-vis, resonance Raman, and NMR spectroscopy revealed the existence of different binding modes for heme-peptide/protein complexes [6]. These investigations resulted in the first structures of heme-peptide complexes known so far [5,7]. Binding data and structural characteristics displayed specific sequence requirements that, in turn, present suitable tools to identify potential heme-regulated proteins and, moreover, open new perspectives for diagnosis and treatment of pathophysiological conditions associated with non-balanced concentrations of bound and free regulatory heme in the organism [6].

References

1.  Kühl, T., Sahoo, N., Nikolajski, M., Schlott, B., Heinemann, S.H., Imhof, D., Chembiochem 2011, 12, 2846-2855.

2. Yao, X., Balamurugan, P., Arvey, A., Leslie, C., Zhang, L., Biochem. Biophys. Res. Commun. 2010, 403, 30-35.

3. Atamna, H., Boyle, K., Proc. Natl. Acad. Sci. USA 2006, 103, 3381-3386.

4. Shimizu, T., J. Inorg. Biochem. 2012, 108, 171-177.

5. Kühl, T., Wißbrock, A., Goradia, N., Sahoo, N., Galler, K., Neugebauer, U., Popp, J., Heinemann, S.H., Ohlenschläger, O., Imhof, D., ACS Chem. Biol. 2013, 8, 1785-1793.

6. Kühl, T., Imhof, D., Chembiochem 2014, 15, 2024-2035.

7.  Brewitz, H.H., Kühl, T., Goradia, N., Galler, K., Popp, J., Neugebauer, U., Ohlenschläger, O., Imhof, D., submitted.