The seven-fold circularized propellar is called a β propellar by the authors.

From the name, it is clear that seven β sheets are needed to give the β subunit of the G protein the correct shape for its function.



You should note that the terms
"β sheet" and "β subunit" share β in their names only by coincidence.

The subunit that carries the propellar could have been called the "α subunit" but by chance it was called the "β subunit".

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