Protein surface recognition by synthetic agents: Design and structural requirements of a family of artificial receptors that bind to cytochrome c

The design, synthesis, and evaluation of a novel series of receptors for pr otein surface recognition are described. The design of these agents is base d around the attachment of four constrained peptide loops onto a central ca lix[4]arene scaffold. This arrangement mimics the role of the hypervariable loops in antibody combining regions and defines a large surface area for b inding to a complementary region of the exterior of a target protein. Using affinity and gel filtration chromatographies we show that one particular r eceptor binds strongly to the surface of cytochrome c. The site of binding is presumably close to the heme edge region, which contains several charged lysine residues. This is supported by the observation that the receptor in hibits the reduction of Fe(III) cytochrome c to its Fe(II) form. We also sh ow that binding is strongly dependent on the nature of the substituents on the lower rim of the calixarene. The nmr and computational studies suggest that this effect may be due to conformational differences among the differe nces substituted receptors. (C) 1998 John Wiley & Sons, Inc.