Electron cryotomography of the E. coli pyruvate and 2-oxoglutarate dehydrogenase complexes.

The E. coli pyruvate and 2-oxoglutarate dehydrogenases are two closely related, large complexes that exemplify a growing number of multiprotein "machines" whose domains have been studied extensively and modeled in atomic detail, but whose quaternary structures have remained unclear for lack of an effective imaging technology. Here, electron cryotomography was used to show that the E1 and E3 subunits of these complexes are flexibly tethered approximately 11 nm away from the E2 core. This result demonstrates unambiguously that electron cryotomography can reveal the relative positions of features as small as 80 kDa in individual complexes, elucidating quaternary structure and conformational flexibility.