Measuring forces between biological macromolecules with the Atomic Force Microscope: characterization and applications

Structure and function in biological macromolecular systems such as proteins and polynucleotides are based on intermolecular interactions that are short ranged and chemically specific. Our knowledge of these molecular interactions results from indirect physical and thermodynamic measurements such as x-ray crystallography, light scattering and nuclear magnetic resonance spectroscopy. Direct measurement of molecular interaction forces requires that the state of a system be monitored with near atomic resolution while an independent force is applied to the system of 10−12 to 10−9 Newton magnitude. The atomic force microscope (AFM) has recently been applied to the study of single molecular interactions. The microfabricated cantilever of the AFM, a force transducer of small yet variable stiffness and high resonance frequency, produces a transducer of 10−15 N/Hz1/2 force sensitivities and 0.01 nm position accuracy.This presentation describes the AFM measurement of the molecular interaction forces in the model ligand-receptor system streptavidin-biotin and between complementary strands of DNA.