Dr. Robert Szoszkiewicz

Biological Sciences, Columbia University, New York, NY

Single-molecule and Local Studies of Mechanical (un)folding of Proteins, Enzymatic Catalysis, and Water Structure at Solid Surfaces

Monday, March 24, 2008

4:00 p.m.

Cardwell 102

With the ability to watch one molecule at a time single-molecule techniques are unique in observing the processes, which otherwise are hidden in macroscopic observables or averaged out by ensemble measurements. In the force-clamp spectroscopy with atomic force microscopy (AFM) piconewtons of force can be applied along a precisely defined direction, and to a single molecule. First, I will show how to identify several distinct regimes associated with (un)folding of single protein molecules, and what kind of physical information can be extracted from there. Mechanical forces exerted on single protein molecules are inherently present in biological systems. Our muscles, cell transport, and cell motility (i.e., ability to move spontaneously) rely heavily on these forces.

Next, I will show how we could have obtained the details of the energy landscape and conformational changes of the substrate-enzyme during an enzymatic catalysis, while using single molecule force-clamp spectroscopy with a particular choice of native enzyme, and an engineered polyprotein.

Finally, in a series of local AFM measurements we studied water molecules confined in sub-nanometer gaps. Water in sub-nanometer gaps defines physical properties of cell membranes, and permeation of ion channels inside each cell membrane. On both hydrophilic and hydrophobic surfaces, we observed the oscillatory solvation forces arising from the density fluctuations within confined water layers, and we obtained an approximate viscosity of each water layer.