Hybrid scanning transmission electron/scanning tunneling microscope system for the preparation and investigation of biomolecules

Structural changes in native membrane proteins monitored at subnanometer resolution with the atomic force microscope: a review

Three membrane proteins, OmpF porin from Escherichia coli, bacteriorhodopsin from Halobacterium salinarium, and the hexagonally packed intermediate (HPI) layer from Deinoccocus radiodurans, were investigated with the atomic force microscope in buffer solution. A resolution of up to 0.8 nm allowed structural differences of individual proteins to be detected. OmpF porin exhibits different static conformations on the outer surface, which possibly represent the two conductive states of the ion channels. Reversible structural changes in the cytoplasmic surface of purple membrane have been induced by changing the force applied to the scanning stylus: doughnut-shaped bacteriorhodopsin trimers transformed into a structure with three pronounced protrusions when the force was reduced from 300 to 100 pN. Furthermore, individual pores of the inner surface of the HPI layer were observed to switch from an "open" to a "closed" state. Together, the structural changes in proteins monitored under physiological conditions suggest that direct observation of function-related conformational changes of biomolecules with the atomic force microscope is feasible.

Progress in the application of scanning probe microscopy to biology

Several key developments have occurred recently in the application of scanning probe microscopy to biology. These include the use of 'tapping-mode' atomic force microscopy both for the high-resolution imaging of biomolecules in liquids and for monitoring in situ biocatalysis, the use of atomic force microscopy as a force transducer to measure individual biological interactions, and the development of hybrid techniques such as scanning tunnelling microscopy coupled to confocal scanning laser microscopy.