Structure of the γ subunit and active site of QHNDH.
(A) The backbone ribbon is blue, the crosslinked side
chains of Cys are yellow, and the crosslinked side chains of
tryptophylquinone (Trq), Glu, and Asp are red. (B)
Electron density around CTQ. Also shown are the putative active site
base Asp-33γ, its covalently linked Cys-27γ, the molecule of
t-butyl alcohol (tbu) and the sodium ion (Na). Only
Cα and side chain atoms are included. The map was computed
with coefficients (2Fo −
Fc) exp(−iα) where
Fc and α, the calculated structure factors
and phase angles, were derived from the final refined model. The
contours are drawn at 1.2 σ, where σ is the rms value of the
electron density. This diagram was prepared by using
TURBO-FRODO (18). (C) Stereoview of
the active site of QHNDH. See text for details.