Tyrosine-heme ligation in heme-peptide complex: design based on conserved motif of catalase.

On the basis of evolutionary conservation of sequence in catalases, we have designed a heme-binding peptide (Ac-RLKSYTDTQISR12-(GGGG)-CRIVHC22-NH2) for the 'redox activity modulation' of heme. Heme-binding studies showed a blue-shifted Soret (369 nm) in the presence of TFE and a red-shifted Soret (418 nm) in the absence of TFE. These blue- and red-shifted Sorets suggest ligation through tyrosinate and histidine, respectively. This is the first designed peptide ligating to heme through tyrosine. NMR studies have confirmed that tyrosine ligation to heme in this heme-peptide complex occurs only in the presence of TFE. We suggest that TFE induces helicity in the peptide and brings the arginine and tyrosine in proximity, resulting in ionization of the phenolic side chain of tyrosine. In the absence of TFE, the unstructured peptide lacks the intra-molecular Arg(+)Tyr(-) ion pair, allowing heme binding to histidine. This peptide has significant peroxidase activity though it does not have catalase activity.