Single-Cell Biophysics: Measurement, Modulation, and Modeling

Single-Cell Biophysics: Measurement, Modulation, and Modeling

Poster Abstracts

49-POS Board 25 Mechano-Chemical Regulation of Actin Depolymerization Kinetics Cho-yin Lee 1,2,3 , Jizhong Lou 4 , Kuo-Kuang Wen 5 , Melissa McKane 5 , Suzanne G. Eskin 1 , Peter A. Rubenstein 5 , Shu Chien 7 , Ono Shoichiro 6 , Cheng Zhu 1 , Larry V. McIntire 1 . 1 Georgia Institute of Technology, Atlanta, GA, USA, 2 National Taiwan University Hospital, Taipei City, Taiwan, 3 Taoyuan General Hospital, Ministry of Health and Welfare, Taoyuan City, Taiwan, 4 Chinese Academy of Sciences, Beijing, China, 5 University of Iowa, Iowa City, IA, USA, 6 Emory University, Atlanta, GA, USA, 7 University of California at San Diego, La Jolla, CA, USA. A fundamental yet unresolved issue in cell biology is how force regulates actin dynamics and how this biophysical regulation is modulated by biochemical signaling molecules. Here we show, by atomic force microscopy (AFM) force-clamp experiments, that tensile force regulates the kinetics of G-actin/G-actin and G-actin/F-actin interactions by decelerating dissociation at low forces (catch bonds) and accelerating dissociation at high forces (slip bonds). Steered molecular dynamics (SMD) simulations revealed force-induced formation K113: E195 salt bridge between actin subunits. This provided a structural mechanism for actin catch bonds, supported by the mutagenesis study showing that the K113S, K113E, E195S, E195K mutants of yeast actin suppressed the actin catch bonds; and that this suppression is rescued by a K113E/E195K double mutant (E/K) restoring the interaction in the opposite orientation. Moreover, formin controlled by RhoA-mediated auto-inhibitory module can serve as a "molecular switch", converting the catch-slip bonds to slip-only. These results demonstrate the mechano-chemical regulation of the actin depolymerization kinetics by catch-slip bonds. They also support biological significance of actin catch-slip bonds, as they corroborate reported observations that RhoA and formin switch force-induced actin cytoskeleton alignment and that either K113E or E195K induces yeast cell growth defects rescued by E/K. Our study may provide a mechanoregulatory mechanism to control cell functions by regulating the depolymerization kinetics of force-bearing actin filaments throughout the cytoskeleton.

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