Biophysical Society Thematic Meeting | Canterbury 2023

Towards a More Perfect Union: Multi-Scale Models of Muscle and Their Experimental Validation

Poster Abstracts

19-POS Board 19 COOPERATIVE BINDING OF MYOSIN-NUCLEOTIDE COMPLEX AND UNREGULATED F-ACTIN Aarushi Naskar 1 ; Alexis Johnson 1 ; Mitchell Turk 1 ; Yuri Nesmelov 1 ; 1 UNC Charlotte, Physics, Charlotte, NC, USA In the actomyosin cycle myosin hydrolyses ATP and binds actin, initially weakly and then strongly. The timing of myosin ATP hydrolysis and subsequent binding to actin remains elusive. We performed a double-mixing transient experiment to characterize the kinetics of actomyosin interaction shortly after ATP binding to myosin. In the experiment we first rapidly pre-mix rabbit skeletal myosin S1 and equimolar ATP, thus producing myosin-ATP complex. After a controlled delay we rapidly add unregulated F-actin to the mixture to observe the interaction of actin with myosin-ATP complex. We detect transients of the light scattering after the second mixing. A sigmoid-shaped curve of transients was observed, which is a sign of cooperative binding. This is in contrast to an exponential curve, usually observed when myosin S1 is rapidly mixed with unregulated F-actin without the presence of any nucleotide, as expected for the well-known strong non-cooperative binding of actin and myosin. We consider several models to explain the observed transients of actin and myosin-ATP complex: a non-cooperative binding, the cooperative single-contiguous and doubly-contiguous actomyosin binding. We conclude that the model of the doubly-contiguous actomyosin binding fits best the observed transients. We conclude that in the presence of physiological ATP concentration, myosin binds actin cooperatively, even without the regulatory proteins of the thin filament.

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