Bovine mitochondrial c8 ring

With only 8 members in the ring, the packing is not very tight.

One possibility is that lipids fill in the gaps.

Glu 58 is colored red.

Bioenergetic cost of making an adenosine triphosphate molecule in animal mitochondria. Watt, I.N., Montgomery, M.G., Runswick, M.J., Leslie, A.G.W., Walker, J.E.,
(PubMed)

2xnd (PDB)

 alkaliphilic cyanobacterium: Spirulina platensis c15 ring

With 15 subunits, the packing is tight.

Glu 62 is colored red.

Pogoryelov D, Yildiz O, Faraldo-Gómez JD, Meier T.: High-resolution structure of the rotor ring of a proton-dependent ATP synthase. Nat Struct Mol Biol. 2009 Oct;16(10):1068-73. (PubMed)

2wie (PDB)