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Figure 1.
Structures of PA26-proteasome complexes. A, overall structure
with one PA26 subunit colored blue and its three C-terminal
residues in space-filling representation. Proteasome subunits
that form the corresponding binding pocket are pink and gray
(white in subsequent panels). B, close-up showing main chain
hydrogen-bonding interactions of the PA26 C-terminal residues
(31). C, sequences and structures of PA26 (31) and variants
described in this work shown after overlap on the proteasome
structures. D, the penultimate Tyr-230 residue contacts Gly-19
to reposition the Pro-17 turn. Distances between Tyr-230-OH and
Gly-19-O in closed (red; modeled) and open (green; observed)
conformations are shown. Pro-17 undergoes an apparent movement
of ∼1 Å. H0, helix 0. E, binding pocket with proteasome
shown as a semitransparent molecular surface. Conserved residues
whose side chains contact the activator C-terminal residues are
indicated. F, V230F penultimate phenylalanine interactions
observed with Gly-19 in the open conformation (pink) and modeled
in the closed conformation (blue). To best describe contacts,
riding hydrogen atoms were included in determined structures and
assessed with MolProbity (36).
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