Maximum likelihood estimation of multiple-bond kinetics from single-molecule pulling experiments

Kinetic parameters associated with bond dissociation have been identified from experiments in which mechanical forces exerted by atomic force microscopy or laser tweezers are used to break bonds in single molecules. Analysis of a single-bond microscopic model indicates that the breakage frequency distribution is most sensitive to the value of the distance to the free-energy minimum barrier and least sensitive to the molecular spring constant. This analysis plus limitations in the single-bond microscopic model motivate a double-bond microscopic model that requires only one additional kinetic parameter. In single-molecule experiments for the neural cellular adhesion molecule (NCAM), the double-bond microscopic model can more accurately describe the breakage frequency distribution for both high and low values of the applied force, which is consistent with the molecular structure of the NCAM determined by a surface force apparatus. This provides a systematic procedure for gaining information on the molecular structure of single molecules by analyzing breakage frequency distributions measured during single-molecule pulling experiments.