Porphyrin, peptide interactions

The energetics of peptide-porphyrin interactions and peptide ligand-metal binding have also been observed in another self-assembly system constructed by Huffman et al. (125). Using monomeric helices binding to iron(III) coproporphyrin I, a fourfold symmetric tetracarboxylate porphyrin, these authors demonstrate a correlation between the hydropho-bicity of the peptide and the affinity for heme as well as the reduction potential of the encapsulated ferric ion, as shown in Fig. 12. These data clearly demonstrate that heme macrocycle-peptide hydrophobic interactions are important for both the stability of ferric heme proteins and the resultant electrochemistry. 

Kawakami, J. Kitano, T. Sugimoto, N., A selection of short peptides that interact with a porphyrin as a small target by immobilized phage display. Chem. Commun. 1999, 1765-1766... 

Another approach is based on n-n stacking, which utilizes the moderately strong interactions between delocalized n-electrons of nanocarbons and those in aromatic organic compounds, such as derivatives of pyrene [54,55], porphyrins [56,57], phthalo-cyanines [58] or combinations thereof [59], as well as peptides [60], DNA [61], benzyl alcohol [62] or triphenylphosphine [63]. These molecules are often modified with long... 

While these complex model heme proteins have a large potential for functionalization, an interesting approach that is very different has been taken by other workers in that the heme itself functions as the template in the formation of folded peptides. In these models peptide-peptide interactions are minimized and the driving force for folding appears to be the interactions between porphyrin and the hydrophobic faces of the amphiphiUc peptides. The amino acid sequences are too small to permit peptide-peptide contacts as they are separated by the tetrapyrrole residue. These peptide heme conjugates show well-re-solved NMR spectra and thus well-defined folds and the relationship between structure and function can probably be determined in great detail when functions have been demonstrated [22,23,77]. They are therefore important model systems that complement the more complex proteins described above. 

These minimalistic peptide scaffolds potentially provide a biologically relevant laboratory in which to explore the details of heme-peptide interactions and, with development, perhaps approach the observed range of natural heme protein fimction. These heme-peptide systems are more complex than typical small molecule bioinorganic porphyrin model compoimds, and yet are seemingly not as enigmatic as even the smallest natural heme proteins. Thus, in the continuum of heme protein model complexes these heme-peptide systems lie closer to, but certainly not at, the small molecule limit which allows for the effects of single amino acid changes to be directly elucidated. 

The formation of axially substituted complexes MLL (M = Zn or Cd H2L = porphyrin L = another ligand) has been investigated by a number of groups.1155-1158 An EXAFS study has shown that there is no short axial Zn—S interaction in peptide-substituted zinc porphyrins, in which the side chain bears a cysteine residue.1159 ... 

The three apparatus for detecting molecular interactions were investigated using the same peptide binder, HASYSC, and the peptides were immobilized in the same manner. All the apparatus show the ability for detection. Of course, porphyrins can be detected by a spectroscopic or florescence detection method however, these apparatus can be applied to substances that do not have spectroscopic or electrochemical properties. 

Sugimoto, N. Nakano, S., Sandwiching interaction of peptides with a porphyrin. Chem. Lett. 1997,939-940... 

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