Design and synthesis of haem-binding peptides. Relationship between haem-binding properties and catalytic activities

We have designed and synthesized two series of amphiphilic two-α-helix peptides, that bound Fe^III-mesoporphyrin (haem) through a ligation of two His residues. The interaction between the peptides and the haem was characterized by UV-VIS and circular dichroism (CD) measurements. The first series of peptides, designed on the basis of the coiled-coil motif, showed a unique haem binding property which was dependent on the concentration of trifluoroethanol (TFE) present. The peptides bound the haem effectively only when the two-α-helix structures were controlled by the addition of 10-25% TFE. These results indicated that the haem binding ability of the peptides could be regulated by the change in peptide conformation with TFE. The second series of two-α-helix peptides, designed on the basis of the amphiphilic α-helix motif, but not of the coiled-coil motif, formed an α-helix structure and bound the haem in a buffer. Furthermore, in the presence of peptides, the haem showed strong induced CD peaks at the Soret region, implying that the haem chromophore was highly oriented in the peptide structures. The catalytic activity of the haem bound to the peptides, which was similar to that of peroxidase, was significantly depressed with increased binding constants and the Soret-CD intensities. It was demonstrated that the catalytic activity of the haem was correlated with the rigidity and orientation of the b-type haem in the polypeptides.