Interaction Forces with Carbohydrates Measured by Atomic Force Microscopy

Studies of carbohydrate-carbohydrate-interactions by atomic force microscopy employing functionalized 4-acetylthio-butyl glucopyranosides

By Fischer glycosylation both anomers of 4-chlorobutyl gluco-as well as galactopyranosides were obtained and transformed into the corresponding 4-acetylthio-butyl glycopyranosides. Dependent on the precursors two straightforward routes were followed to obtain the appropriate 3-O-sulfated derivatives. Unsubstituted and sulfated glucopyranosides were attached to gold surfaces a gold tips. Their interactions were studied using atomic force microscopy for simulations of intercellular glycoside-based interactions and discussed in-depth.

A stochastic, cantilever approach to the evaluation of solution phase thermodynamic quantities

A cantilever device based on competitive binding of an immobilized receptor to immobilized and soluble ligand and capable of measuring solution-phase thermodynamic quantities is described. Through multiple binary queries, the device stochastically measures the probability of the formation of a bound complex between immobilized protein and immobilized ligand as a function of soluble ligand concentration. The resulting binding isotherm is described by a binding polynomial consisting of the activities of soluble and immobilized ligand and binding constants for the association of immobilized protein with free and immobilized ligand. Evaluation of the polynomial reveals an association constant for the formation of a complex between immobilized ligand and immobilized protein close to that for the formation of complex between soluble protein and soluble ligand. The methodology lays the foundation for construction of practical portable sensing devices.

Physical properties of Escherichia coli P pili measured by optical tweezers

The mechanical behavior of individual P pili of uropathogenic Escherichia coli has been investigated using optical tweezers. P pili, whose main part constitutes the PapA rod, composed of approximately 10(3) PapA subunits in a helical arrangement, are distributed over the bacterial surface and mediate adhesion to host cells. They are particularly important in the pathogenesis of E. coli colonizing the upper urinary tract and kidneys. A biological model system has been established for in situ measurements of the forces that occur during mechanical stretching of pili. A mathematical model of the force-versus-elongation behavior of an individual pilus has been developed. Three elongation regions of pili were identified. In region I, P pili stretch elastically, up to a relative elongation of 16 +/- 3%. The product of elasticity modulus and area of a P pilus, EA, was assessed to 154 +/- 20 pN (n=6). In region II, the quaternary structure of the PapA rod unfolds under a constant force of 27 +/- 2 pN (n approximately 100) by a sequential breaking of the interactions between adjacent layers of PapA subunits. This unfolding can elongate the pilus up to 7 +/- 2 times. In region III, pili elongate in a nonlinear manner as a result of stretching until the bond ruptures.