Progress in measuring biophysical properties of membrane proteins with AFM single-molecule force spectroscopy

Membrane proteins are crucial in cell physiological activities and are the targets for most drugs. Thus, investigating the behaviors of membrane proteins not only provide deeper insights into cell function, but also help disease treatment and drug development. Atomic force microscopy is a unique tool for investigating the structure of membrane proteins. It can both image the morphology of single native membrane proteins with high resolution and, via single-molecule force spectroscopy (SMFS), directly measure their biophysical properties during molecular physiological activities such as ligand binding and protein unfolding. In the context of molecular biomechanics, SMFS has been successfully used to understand the structure and function of membrane proteins, complementing the static three-dimensional structures of proteins obtained by X-ray crystallography. Here, based on the authors’ antigen-antibody binding force measurements in clinical tumor cells, the principle and method of SMFS is discussed, the progress in using SMFS to characterize membrane proteins is summarized, and challenges for SMFS are presented.