Simultaneous dynamic stiffness and extension profiles of single titin molecules: Nanomechanical evidence for unfolding intermediates

The stiffness and extension force of single native titin molecules were measured. A molecular imaging PicoSPM AFM with a MAC-mode attachment and breakout box was augmented with an EG&G 7260 lockin amplifier and a Stanford Research Systems SR650 filter to measure force-extension and stiffness-extension curves simultaneously. It was shown that the acquisition of both force and stiffness on single protein molecules molecules was expected to provide new insights into folding intermediate states and elastic force generation in muscle and other soft biological composite material. The amplitude signal from the lockin was buffered and digitized by the auxiliary input on the PicoSPM control electronics.