| Research Abstract |
Iron porphyrins and metals display diverse functions in proteins as cofactors. Over the years, in order to elucidate functions of metallo- and heme-proteins, many studies using synthetic porphyrin compounds and mutated proteins have been carried out. It is not easy, however, to understand deteiled mechanisms of diverse functions of metallo- and hemeproteins, since the natural proteins contain many complicated factors that are inherently independent of the essential for the functions. Thus, it is needed to establish the structural model system which has more native-like properties and remove the complexity of the natural counterpart. Along with this aspect, considerable effort has been devoted to the construction of de novo designed polypeptide 3D structures conjugated with metal and ironporphyrin by chelation or covalent linkage with peptides. However, little is known yet, about the factors that influence the interaction between the iron porphyrin and designed peptides.
In this study, t
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he author have synthesized a variety of originally designed peptides, which are composed of two amphiphilic alpha-helix and bind a metal ion or Fe-mesoporphyrin (heme) through a ligation of two His residues, in order to know the minimal requirements for the construction of stable peptide-metal ion / heme conjugates in water. The peptides demonstrated some requirements for the effective metal ion / heme -binding. That is, the peptide conformation, the hydrophobic and steric interactions between the haem and amino acid-chains at the heme-binding site are important factors that determine the binding constant between the peptides and heme. Furthermore, the author could examine a role of haem cofactor as a structural element and/or effector of artificial designed peptides. It has been demonstrated that the heme-binding significantly affects on the 2D, 3D and 4D structure of designed peptides. Additionally, the catalytic activity of heme bound to the peptides was significantly afected by the heme-binding properties of the peptides, indicating that the function of heme could be partly regulated by the artificially designed peptides, The obtained information will be available for the development of an artificial haemprotein that meets minimal requirements for the function. Less
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