cytochrome-c-t and calix(4)arene

Sulfonato-calix[n]arenes (sclxn) are promising tools to generate crystalline protein frameworks. We report, for the first time, a lower rim functionalised octa-anionic calix[4]arene (sclx4mc) in complex with proteins. Two crystal structures of sclx4mc bound to yeast or horse heart cytochrome c (cytc) are described. Highly porous honeycomb or tubular assemblies were obtained with yeast or horse cytc, respectively. Related frameworks were obtained previously with sclx8 and sclx6 but not with sclx4, suggesting that the ligand charge is a determining factor.

Topics: Animals; Anions; Calixarenes; Crystallization; Crystallography, X-Ray; Cytochromes c; Horses; Ligands; Molecular Structure; Phenols; Porosity; Proteins; Yeasts

Small molecules that recognize protein surfaces are important tools for modifying protein interaction properties. Since the 1980s, several thousand studies concerning calixarenes and host-guest interactions have been published. Although there is growing interest in protein-calixarene interactions, only limited structural information has been available to date. We now report the crystal structure of a protein-calixarene complex. The water-soluble p-sulfonatocalix[4]arene is shown to bind the lysine-rich cytochrome c at three different sites. Binding curves obtained from NMR titrations reveal an interaction process that involves two or more binding sites. Together, the data indicate a dynamic complex in which the calixarene explores the surface of cytochrome c. In addition to providing valuable information on protein recognition, the data also indicate that the calixarene is a mediator of protein-protein interactions, with potential applications in generating assemblies and promoting crystallization.

Topics: Binding Sites; Calixarenes; Crystallography, X-Ray; Cytochromes c; Phenols; Protein Interaction Mapping; Protein Structure, Tertiary; Solvents; Static Electricity

Two novel carboxylphenyl-modified calix[4]arenes, tetrakis-carboxylphenylcalix[4]arene (TCPC) and 1,3-bis-carboxylphenylcalix[4]arene (BCPC), as well as a corresponding analogue for comparison, tetrakis-phenylcalix[4]arene (TPC), have been synthesized by palladium-catalyzed Suzuki cross-coupling of arylboronic acid and tetrabromocalix[4]arene as a key step. The binding properties of these calix[4]arene derivatives with bovine heart cytochrome c (cyt c) in dimethylformamide (DMF) was investigated by fluorescence spectroscopy. The binding affinity in the order of TCPC>BCPC>>TPC reflects a clear dependence on the number of carboxyl ligating groups attached onto a receptor and suggests the electrostatic force may be the predominant factor driving the complexing process. The stable 1:1 complexes of TCPC and BCPC with cyt c were evidenced with the binding constants of 3.15 x 10(6) and 5.85 x 10(5)L mol(-1), respectively. Due to a large overlap between the emission spectrum of TCPC and the absorption spectrum of cyt c, and a short interaction distance (estimated to be 5.6 nm) between them, the fluorescence quenching of TCPC upon complexation with cyt c is attributed to an efficient energy transfer.

Topics: Animals; Calixarenes; Carboxylic Acids; Cattle; Cytochromes c; Dimethylformamide; Energy Transfer; Phenols; Protein Binding; Spectrometry, Fluorescence; Structure-Activity Relationship