The histogram (inset) in c shows the distribution (with the Gaussian fit in red) of the specific interaction forces recorded in the adhesion image; the mean value is approximately 483 pN; b and d AFM topography image and the corresponding adhesion image of the same area of the sample after chemically reducing the core complexes on the surface and imaging in the dark. VX-680 The black arrows in c and d indicate two high-force non-specific

interactions that were not affected by the change in the redox conditions; e 3D composite images (topography combined with adhesion skin) of the specific unbinding Selleck SB431542 events from a and c; f as for e, but with data from b and d. In panels c–f, the colour coding is as follows: the red colour corresponds mTOR inhibitor to the specific events (high unbinding force), while the beige colour corresponds to the non-specific interactions. The scale bar in all panels is 100 nm Since interaction with the tip-bound reduced cyt c 2-His6 requires

that the surface-bound RC-His12-LH1-PufX complexes are in the oxidised state, (RC[ox]), we performed a control experiment by chemically reducing the RC-His12-LH1-PufX complex while conducting the AFM measurements in the dark to prevent RC photo-oxidation. Topographic and adhesion images were recorded over exactly the same area of the sample: the topography of the sample, Fig. 3b, is unchanged while the 137 high unbinding force events in the adhesion map, Fig. 3d, decreases to only 25—a significant drop by a factor of 5.5. This is an unambiguous indication that the high adhesion force events we observed in the adhesion images are associated with a specific interaction promoted by photooxidation Florfenicol of the RC. It is worth noting that some high-force unbinding events remained

unaffected by the change in the redox conditions, indicated with the black arrows in Fig. 3c, d, but they do not correlate with RC-His12-LH1-PufX molecules as evident from the 3D composite representations in Fig. 3f. Single-molecule force spectroscopy study of the interactions between monomeric RC-LH1-PufX core complex and the cytochrome c 2 electron carrier PF-QNM is a new method for simultaneously imaging the surface topography and the distribution of intermolecular forces, but there is a more established method, SMFS, for quantifying intermolecular forces (Bonanni et al. 2005), although not their surface distribution. Although the mapping aspect is an important part of our aims the conventional SMFS approach still provides a useful validation of our experimental system, and of the specificity of the interactions observed between the RC-His12-LH1-PufX and cyt c 2 proteins.