ATP synthase

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Index:

I. ATP synthase.

F1 is the catalytic part of ATP synthase which projects inward from inner mitochondrial membranes. Walker and coworkers have solved its structure to 2.8 A resolution.

The quaternary structure of F1 consists of 3 each of alternating alpha and beta subunits forming a cylindrical complex attached to the membrane-embedded F0 proton channel. The central cavity of the cylinder is occupied by by the alpha-helical C-terminal domain of the gamma subunit [fig. 1 from Cross]:

From Abrahams et al: "...the three catalytic beta-subunits differ in conformation and in the bound nucleotide. The structure supports a catalytic mechanism .. in which the three catalytic subunits are in different states of the catalytic cycle at any instant. Interconversion of the states may be achieved by rotation of the alpha3beta3 subassembly relative to an alpha-helical domain of the gamma-subunit."

Animated cartoon of ATP synthase in action:

This cartoon is adapted from fig. 2 of Cross. The 3 shades of red represent the 3 different conformational states of the catalytic subunits. The central asymmetric black object represents the gamma subunit which is caused to rotate by the mitochondrial proton efflux. This rotation drives the conformational transitions of the catalytic subunits which, in turn, alters the nucleotide binding site affinities. As a consequence, conformational energy flows from the catalytic subunit into the bound ADP and P_i to promote their dehydration into ATP.

Note that, when "uncoupled", i.e., dissociated from a proton gradient, ATP synthases act as ATPases. The ATP-coupled proton transporters associated with Golgi membranes are structurally similar to the ATP synthases.

Abrahams JP, et al, 1994 Nature 370:621.
Cross RL, 1994 Nature 370: 594.