Book of Abstracts: Albany 2009
June 16-20 2009
© Adenine Press (2008)
Three-Dimensional Structure of the Escherichia coli F1-ATPase in a Self-inhibited Conformation
We report the crystal structure of the E. coli F1-ATPase (EcF1) depleted of the δ-subunit, at 3.3 Å resolution. The structure was solved by a combination of molecular replacement and 4-fold non-crystallographic symmetry averaging, which yielded an electron density map of excellent quality. The sequences of the entire α3&beta3γε subunits (M.W. ∼375kDa) were unambiguously interpreted using selenomethionine-labeled protein. The general architecture of the α3β3γ ?core? is similar to that of the bovine mitochondrial F1 (MF1), but with greater asymmetry between pairs of αβ subunits. The conformation of ε (δ in MF1) is the most striking feature. Unlike δ in MF1, ε?s C-terminal domain (CTD) adopts a highly extended state: helix-1 extends up to pack on one side of γ?s ?foot? domain, the following loop packs below the ?DELSEED? motif of subunit βDP, and helix-2 inserts into the central cavity of EcF1 to form an antiparallel trimeric coiled-coil with part of γ?s N-terminal helix. This interaction blocks specific contacts between γ and the CTDs of αDP/βDP subunits, which are shifted away from γ?s central rotary shaft. Terminal residues of the ε-subunit adopt a non-helical conformation that embrace both γ-subunit helices and extend across the central cavity to contact βTP near the inner surface of its catalytic nucleotide-binding site. Overall, intrusion of ε?s CTD into the central cavity is likely to block subunit motions involved in the rotary catalytic cycle of F1 or the intact ATP synthase (FOF1). This structure sheds light on an inhibitory mechanism that is unique to bacterial and chloroplast ATP synthases.
SUNY Upstate Medical University