Watching the walk: observing chemo-mechanical coupling in a processive myosin motor.

Molecular motors are cellular nanomachines that convert the energy from nucleotide binding, hydrolysis, and product release into mechanical work. Because molecular motors contribute to fundamental processes in all living organisms, including genome replication, gene transcription, protein synthesis, organelle transport, and cell division, understanding how the chemical (ATP utilization) and mechanical (motility) cycles are linked is of fundamental importance. A recent study reports the direct visualization of simultaneous nucleotide binding and mechanical displacement of a single myosin 5a molecule, a processive molecular motor protein that takes successive approximately 36-nm steps along actin filaments of the cytoskeleton. This new work demonstrates an exciting advance in single-molecule enzymology and advances our understanding of the link between chemical catalysis and mechanical work in molecular motors, particularly those that operate under internal and external loads.