X-ray crystallography and electron microscopy can each provide a wealth of structural information about proteins and other biomolecules. But neither technique can operate under physiologically relevant conditions, so they’re unable to observe the dynamic processes that are central to proteins’ biological function. Atomic force microscopy, on the other hand, can work in water. Now Duckhoe Kim and Ozgur Sahin of Columbia University have used that capability to create a specialized atomic force microscope (AFM) that can locate specific chemical groups in a protein under biological conditions.1
From their AFM tip the researchers dangle two single-stranded DNA hexamers, shown in figure 1 in red and green. The complementary strands, shown in like colors, are attached to a protein’s chemical groups of interest and serve as imaging labels. Whenever one of the hexamers comes into contact with its complement, the two strands briefly bind, and the AFM cantilever is observed to...
