| Abstract: | Complex formation between cationic cytochrome c and the water‐soluble, poly‐anionic p ‐phosphonatocalix6]arene (pclx6) was investigated. A crystal structure (at 1.8 Å resolution) revealed a remarkable dimeric disc of pclx6 that acts like glue to mediate a symmetric (C 2) protein dimer. The calixarene disc has a diameter of about 1.5 nm and masks about 360 Å2 of protein surface. The key protein–calixarene contacts occur via two linchpin lysines, with additional contacts provided by a small hydrophobic patch. The protein–calixarene supramolecular assemblies were observed in solution by size‐exclusion chromatography with multi‐angle light scattering and NMR spectroscopy. Using isothermal titration calorimetry and NMR data, an apparent K d in the low micromolar range was determined for the charge‐rich protein–calixarene complex. In contrast to p ‐sulfonatocalix4]arene, the larger pclx6 has a single, well‐defined binding site that mediates the assembly of cytochrome c in solution. |
