Peptide design based on an antibody complementarity-determining region (CDR): construction of porphyrin-binding peptides and their affinity maturation by a combinatorial method.

We have utilized sequence information from an antiheme monoclonal antibody to develop novel porphyrin-binding peptides. Several peptides which have an intramolecular disulfide bond in different positions and different chain lengths were prepared. The affinities of peptides for meso-tetrakis(4-carboxyphenyl)porphyrin were increased by an appropriate conformational restraint using a disulfide bond. Detailed studies with a representative 12-peptide, 12C4, whose length was reduced from 20 residues of the complementarity-determining region (CDR), indicated that both the hydrophobic and electrostatic interactions were essential factors in the peptide-porphyrin binding. Moreover, two-dimensional 1H NMR spectroscopy revealed the conformation of the peptide and the critical residues for the porphyrin-binding. According to the obtained results, a further minimized 9-peptide, 9L, was successfully redesigned with a sequence capable of forming a beta-turn instead of a disulfide bond. Furthermore, affinity maturation studies of 9L were performed by using a combinatorial approach such as the spot-synthesis method. Peptides with an improved affinity for porphyrins were prepared by systematic amino acid replacement. Thus, the design of peptides targeted to porphyrins was demonstrated by the combination of antibody information and the rationally designed combinatorial method.