Ligand-Induced Structural Changes in Maltose Binding Proteins Measured by Atomic Force Microscopy

We use atomic force microscopy (AFM) based force-compression measurements to probe the ligand-induced functional conformational changes in surface-immobilized dicysteine-terminated maltose binding proteins (dicys-MBPs). The proteins are immobilized at well-defined locations directly on Au substrates using the previously reported technique of nanografting. By measuring the difference between the ligand-free and ligand-bound mechanical work performed by the AFM-tip during the protein compression, we determine the open-closed transition energy for dicys-MBPs to be ΔE0 ) (8 ( 4) Kcal/mol. We also compare the binding kinetics of two different ligands (maltose and maltotriose) to dicys-MBPs by performing AFM-friction measurements. We show that our results are consistent with a simple model for the surface-immobilized dicys-MBPs: the protein consists of two rigid lateral lobes connected by a hinge-loaded spring.

http://pubs.acs.org/cgi-bin/asap.cgi/nalefd/asap/html/nl801553h.html

Enhanced Cellular Activation with Single Walled Carbon Nanotube Bundles Presenting Antibody Stimuli

Efficient immunotherapy can be accomplished by expanding T cells outside the body using single walled carbon nanotube (SWNT) bundles presenting antibody stimuli. Owing to the large surface area of these bundles, which can reach 1560 m2/g, T cell stimulating antibodies such as anti-CD3, can be presented at high local concentrations inducing potent activation of T cells. We show that anti-CD3 adsorbed onto SWNT
bundles stimulate cells more effectively than equivalent concentrations of soluble anti-CD3. Stimulation by antibody adsorbed onto SWNT is significantly higher than other high surface area materials (activated carbon, polystyrene, and C60 nanoparticles), suggesting unique properties of SWNT bundles for stimuli presentation. We demonstrate the surface area tunability of these bundles by chemical treatment and its effect on antibody adsorption and subsequent T cell activation. In addition, the T cell response varied with the concentration of SWNT in a concentration dependent manner. Antibody stimuli adsorbed onto SWNT bundles represent a novel paradigm for efficient activation of lymphocytes, useful for basic science applications and clinical immunotherapy.

http://pubs.acs.org/cgi-bin/article.cgi/nalefd/2008/8/i07/pdf/nl080332i.pdf