Invited Paper NS+SP-TuM5
Chemically-specific Intramolecular Imaging with Atomic Force Microscopy

Tuesday, October 20, 2015, 9:20 am, Room 212B

Atomic force microscopy (AFM) is a powerful tool for imaging and chemical characterization of biological samples at molecular resolution in physiologically relevant environments. However, the localized tip-sample interactions limit high-resolution images to the topmost layer of surfaces. Consequently, characterizing the three-dimensional (3-D) inner structures of molecules has been a challenge. Here we demonstrate three-dimensional localization of chemical groups within a protein complex using AFM. We employ short DNA sequences to label specific chemical groups inside the protein complex. T-shaped cantilevers functionalized with complementary probe DNAs allow locating each label with sequence specificity and sub-nanometer resolution. We measure pairwise distances between labels and reconstruct the 3-D loci of the target groups using simple geometric calculations. Experiments with the biotin-streptavidin complex showed that the 3-D loci of carboxylic acids of biotins are within 2-Angstroms of their respective 3-D loci in the corresponding crystal structure, suggesting AFM may complement existing structural biological techniques in solving structures that are difficult to study due to their size and complexity.