Molecular Addressability of Lipid Membrane Embedded Calixarenes towards Cytochrome C

By means of the atomic force microscopy techniques we studied the surface topography of the supported bilayer lipid membranes (sBLM) composed of 1,2-sn-glycerodimyristoylfosfatidylcholine (DMPC) with incorporated calixarenes tOct [6]CH2COOH (CX) specific to cytochrome c (cyt c). It is supposed that cyt c interacts with CX through amino groups of lysine residues at its surface. Therefore we also applied single molecule force spectroscopy (SMFS) to analyze the mechanisms of interaction of cyt c with the CX. In later case cyt c or individual NH2 group have been connected to the AFM tip through special linker. The topography of bare sBLM in a gel state (T=19oC) revealed relatively smooth surface (RRMS=0.18 nm) and thickness ~5.1 nm which agrees well with previous studies. Incorporation of CX into DMPC bilayer resulted in increase of the surface roughness (RRMS= 0.39 nm) and in increase of thickness in average by 0.5 nm. The incubation of the layer with30 nM of cyt c resulted in a surface smoothing (RRMS=0.32 nm) and in a further increase of the thickness between 0.7 to 1.2 nm. The SMFS experiments with cyt c modified AFM tips approved its specific binding to CX and allowed us to determine the binding parameters koff (1.14 ± 0.59 s-1) and xβ (3.98 ± 0.63A). SMFS experiments with an amino-ended linker also resulted in highly specific interactions with comparable values for koff (2.74 ± 0.66 s-1) and xβ (5.91 ± 2.55 A). This suggests that both electrostatic and amino group specific interactions between cyt c and CX cavity exist.