Structural biology: Proton-powered turbine of a plant motor

ATP synthases are enzymes that can work in two directions to catalyse either the synthesis or breakdown of ATP, and they constitute the smallest rotary motors in biology. The flow of protons propels the rotation of a membrane-spanning complex of identical protein subunits, the number of which determines the efficiency of energy conversion. This proton-powered turbine is predicted to consist of 12 subunits, based on data for Escherichia coli. The yeast mitochondrial enzyme, however, has only 10 subunits. We have imaged the ATP synthase from leaf chloroplasts by using atomic force microscopy and, surprisingly, find that its turbine has 14 subunits, arranged in a cylindrical ring.

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