The motor protein kinesin 'walks' by alternately advancing its two motor structural domains. A cutting-edge, single-molecule fluorescence technique reveals further details of this stepping mechanism. Suppose that walking required energy input in the form of, say, one Gummi bear for every step. In what position would you pop the next Gummi bear into your mouth? When one foot is firmly planted on the ground while the other is lifted up and poised next to it to be thrust forward, or when both feet are on the ground spaced apart at step size? Mori et al. (page 750 of this issue) have addressed these questions, not in a person, but in a miniature, biological walking machine — the molecular motor protein kinesin.
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