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Resolving Spatial Conformations of Immuno-Proteins with Cryo-Atomic Force Microscopy (Cryo-Afm)

A major advantage of atomic force microscopy (AFM) is its intrinsic high contrast, owing to its extremely high sensitivity to height variations. For clean, flat specimens, high-resolution images of a variety of bio-molecules have been obtained, demonstrating the usefulness of AFM in structural biology. However, for large molecular complexes, the effectiveness of AFM is seriously limited, partly owing to the excessive deformation induced by the probe force exerted on the specimen. To overcome this difficulty, we have developed a cryo-AFM, operated under liquid nitrogen vapor at a temperature only a few degrees above 77K. In this system, specimen or tip contamination is significantly reduced, and the resolution achieved with isolated macromolecules is generally higher than that obtainable at room temperature with AFM. Therefore, cryo-AFM has been proven to be a worthy alternative for conventional electron microscopy (EM) with the potential of higher resolution without image averaging. A particularly fruitful application of cryo-AFM is the study of the spatial structure of several immuno-proteins, where the 3D surface topology of the molecule has been obtained.