3 years ago

Protein Dimerization on a Phosphonated Calix[6]arene Disc

Protein Dimerization on a Phosphonated Calix[6]arene Disc
Aishling M. Doolan, Martin L. Rennie, Colin L. Raston, Peter B. Crowley
Complex formation between cationic cytochrome c and the water-soluble, poly-anionic p-phosphonatocalix[6]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 (C2) 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 Kd in the low micromolar range was determined for the charge-rich protein–calixarene complex. In contrast to p-sulfonatocalix[4]arene, the larger pclx6 has a single, well-defined binding site that mediates the assembly of cytochrome c in solution. Calixarene contact: Phosphonato-calix[6]arene acts like molecular glue to prompt assembly of cyt c at both low and high salt concentrations. A crystal structure revealed a dimeric disc of the calixarene sandwiched between two proteins. Self-assembly in solution was observed by size exclusion chromatography with multi-angle light scattering, NMR spectroscopy, and isothermal titration calorimetry.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/anie.201701500

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