Abstract
The design of protein-based single molecule sensors and nanostructures for micromachines requires a thorough understanding of the mechanical properties and functional stability of the protein building blocks. Immobilization of these structures at interfaces is an important part of their utility in nanotechnology. Meniscus forces have been shown to linearize and stretch biopolymers such as DNA, polysaccharides, and the giant protein, titin. Here we report that "molecular combing" can also effect the forced unfolding of proteins. As revealed by non-contact mode atomic force microscopy (AFM), meniscus forces can have a profound effect upon the conformation of the small, 16 kDa calcium sensor protein, calmodulin. Individual calmodulin molecules immobilized on a mica surface appear as dumbbells with a separation of ∼18 nm in an aqueous environment. This separation is three-fold larger than the 5 nm distance that spans the two globular domains in crystal structure. These globular domains must be partially unfolded mechanically by interfacial forces.