β-Catenin as a Tension Transmitter Revealed by AFM Nanomechanical Testing

Abstract

β-Catenin, a component of adherens junction (AJ), transmits forces between cells and stabilizes their balance, thereby contributing to AJ maturation. A previous study based on a single-molecule experiment has suggested that β-catenin unfolds under tension with low mechanical stability, while another study showed its mechanical behavior bearing to high forces. Such discrepancy in mechanical behaviors of β-catenin could be a result of experimental conditions such as solvent compounds, pH, and temperature. In the present study, we successfully tested the mechanical behaviors of β-catenin in a simple experimental condition by employing atomic force microscopy (AFM). To perform nanomechanical testing in phosphate-buffered saline buffer without protein aggregation, we directly modified the AFM probe with β-catenin in a low concentration. We performed two types of experiments, in which a part and a whole structure of β-catenin were loaded under tension. The results of the testing indicated that β-catenin behaves as a nonlinear elastic material under tension, i.e., a mechanical component with low stiffness under low tension and high stiffness under high tension. The nonlinear elastic behavior exhibited in our experiment suggests a mechanical function of β-catenin to serve as a tension transmitter at AJs: (1) preserving links between AJ molecules under low tension and (2) transmitting high tension with high mechanical stability.