These findings are critical to take into account in a model relating Pi-release to force generation.
However, it is controversial whether the main force-generating structural change, the powerstroke, gates Pi-release or vice versa 7, 10, 12, 15, 16, 21, 24, 26, 27, 28, 29, a lack of insight that hampers understanding of the transduction process.Įxperiments that combine transient biochemical kinetics with time-resolved fluorescence resonance energy transfer (FRET) for powerstroke detection provide particularly compelling evidence that Pi-release occurs after the powerstroke 7, 8. The process underlies critical cell and body functions 1, 2, 3 in animals and plants from muscle contraction over non-muscle cell motility and intracellular transport to cell signaling. Utilization of the chemical free energy of ATP (We use the abbreviation ATP and ADP while recognizing that MgATP and MgADP are the actual substrate and product, respectively.) for force- and motion-generation by myosin molecules in their interaction with actin filaments, is a prime example of chemomechanical energy transduction in biology. In addition to revealing critical features of energy transduction by actomyosin, the results suggest enzymatic mechanisms of potentially general relevance.
It is also consistent with high-speed atomic force microscopy movies of single myosin II molecules without Pi at the active site, showing consecutive snapshots of pre- and post-power stroke conformations. The model is based on our evidence from kinetics, molecular modelling and single molecule fluorescence studies of Pi binding outside the active site. Here, we present a model with multistep Pi-release that unifies current conflicting views while also revealing additional complexities of potential functional importance. The relationship between release of the ATP hydrolysis product ortophosphate (Pi) from the myosin active site and the force-generating structural change, the power-stroke, remains enigmatic despite its central role in energy transduction. Muscle contraction and a range of critical cellular functions rely on force-producing interactions between myosin motors and actin filaments, powered by turnover of adenosine triphosphate (ATP).
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