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Tannerella forsythia is among the most potent triggers of periodontal diseases, and approaches to understand underlying mechanisms are currently intensively pursued. A similar to 22-nm-thick, 2D crystalline surface (S-) layer that completely covers Tannerella forsythia cells is crucially involved in the bacterium-host cross-talk. The S-layer is composed of two intercalating glycoproteins (TfsA-GP, TfsB-GP) that are aligned into a periodic lattice. To characterize this unique S-layer structure at the nanometer scale directly on intact T. forsythia cells, three complementary methods, i.e., small-angle X-ray scattering (SAXS), atomic force microscopy (AFM), and single-molecular force spectroscopy (SMFS), were applied. SAXS served as a difference method using signals from wild-type and S-layer-deficient cells for data evaluation, revealing two possible models for the assembly of the glycoproteins. Direct high-resolution imaging of the outer surface of T. forsythia wild-type cells by AFM revealed a p4 structure with a lattice constant of similar to 9.0 nm. In contrast, on mutant cells, no periodic lattice could be visualized. Additionally, SMFS was used to probe specific interaction forces between an anti-TfsA antibody coupled to the AFM tip and the S-layer as present on T. forsythia wild-type and mutant cells, displaying TfsA-GP alone. Unbinding forces between the antibody and wild-type cells were greater than with mutant cells. This indicated that the TfsA-GP is not so strongly attached to the mutant cell surface when the co-assembling TfsB-GP is missing. Altogether, the data gained from SAXS, AFM, and SMFS confirm the current model of the S-layer architecture with two intercalating S-layer glycoproteins and TfsA-GP being mainly outwardly oriented. Copyright (c) 2013 John Wiley & Sons, Ltd.

Fibrin aggregation is of vital importance in many physiological and pathological processes, such as blood coagulation, wound healing, and thrombosis. In the present study, we investigated the forces involved in the initial steps of the fibrinogen fibrin aggregation by force spectroscopy using the atomic force microscope. Our data confirm the existence of strong specific interactions between fibrin and fibrin (ogen), with unbinding forces ranging from 290 to 375 pN and a logarithmic dependence on the loading rate between 0.8 and 23 nN/s. (c) 2007 Wiley Periodicals, Inc.

The molecular processes based on the specific receptor-ligand interactions (e.g. immune response to a foreign antigen, communication between nerve cells, etc.) are essential for a good and stable performance of living organisms. The aim of the present work is to study such molecular processes with the Atomic Force Microscope (AFM) operated in Force Spectroscopy (FS) mode. Information such as the force and length of the ligand-receptor bond rupture could be obtained from the standard quasistatic FS studies, whereas no external dithering applied to the AFM tips. Firstly, the antigen-antibody interactions were examined with the Bovine Serum Albumin (BSA) protein and its poly- and two different monoclonal antibodies. It was shown that the peak unbinding force depends on the type of antibody and the antibody concentration. The single potential barrier is dominant for the interaction between BSA and monoclonal antibodies and was revealed from the loading rate-dependent measurements. Secondly, we are interested in the process of fibrin gel formation, in particular in the forces involved in this process. It was demonstrated that the fibrin-fibrinogen interaction is the specific one. The unbinding force rupture for single fibrin-fibrin(ogen) complex was determined to be of about 320 pN at a loading rate of 3.5 nN/s. The single potential barrier is also dominant for this interaction. Moreover, a new method of direct and continuous measurement of the spring constant of single molecules or molecular complexes has been elaborated in our laboratory. To this end, the standard FS technique with functionalized tips and samples is combined with a small dithering of the AFM tip. The change of the dithering amplitude as a function of the pulling force is measured in order to extract the spring constant of the complex. The potentialities of this technique were demonstrated for the experiments with single BSA – polyclonal antibody to BSA (Ab-BSA) and fibrinogen – fibrinogen complexes.