High-Resolution Imaging and Force Measurement of Individual Membrane Proteins by AFM

Abstract

Atomic force microscopy (AFM) has developed into a powerful tool in biophysics to assess the structure and measure the inter- and intramolecular forces of biological objects. At the cutting-edge, imaging and force measurements are performed on individual membrane proteins. Here, recent achievements of high-resolution imaging and imaging in combination with controlled force measurement using AFM are reviewed. High-resolution imaging can yield topographical information to ∼ 10 Å resolution. The comparison with protein structures from X-ray crystallography shows that surface protruding loops of no more than 5 aminoacids are reliably contoured. Force measurements reveal intramolecular forces with a precision of ∼ 10 pN. Again, the comparison with atomic structures shows that forces between pairs of transmembrane helices are probed. As a major advantage, the combination of force spectroscopy measurements with high resolution imaging allow assignment of measured unfolding events with topographical changes. Keywords: AQP1, Escherichia coli aquaporinZ, X-ray crystallography, Blastochloris viridis Core-Complex, Surface layers (S-layers), Halobacterium Salinarum Bacteriorhodopsin