Snapshot view of the V-ATPase molecular machine: animals vs. fungi
The V-ATPase molecular machine pumps hydrogen ions across membranes in the cell using a spinning ring. In yeast and other fungi, the ring has six copies of three different proteins (pink, blue, and yellow). In animals, the ring has six copies of two different proteins (pink and green). The circular ring (right) is shown in flat form like a map of the planet. The proteins assemble by contacting each other using specific interfaces, only some of which are compatible with each other (shown as triangles, squares, and circles).
In the study, ring proteins from the ancestor of all fungi (gray circle) and from the common ancestor of animals and fungi (black circle) were resurrected and experimentally characterized. The proteins that make up the more complex ring were found not to have gained any new functions, but they had lost some of those present in the ancestral proteins.
During the interval when complexity increased (red box), a single, simple mutation in the blue protein and another in the yellow caused each to lose an interaction interface that was present in their more versatile green ancestor. As a result, the blue and yellow proteins became limited to specialized positions in the ring; both became necessary components of a more complex machine.
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