Imaging the native structure of the chaperone protein GroEL without fixation using atomic force microscopy

Most sample preparation methods for scanning probe or electron microscopy require that biomolecules, such as proteins, be fixed. Fixation destroys the molecular functionality and can possibly affect the true molecular structure. Here we report sample preparation conditions that allow the imaging of an unfixed protein, GroEL, under in-vivo conditions, by atomic force microscopy. Under these conditions, the protein should maintain its native structure and biological activity. The typical toroidal shape with pore of the GroEL complex was easily visible in the images. Images of a single complex show dimensions that agree well with crystallographic data. Under in-vivo conditions, it should be possible to study the biological activity and function of proteins.