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Figure 2.
Figure 2: Structure of PA26. a, PA26 heptamer coloured by
monomer. b, Monomer coloured by secondary structure. This
orientation corresponds to the magenta monomer in a. c,
Proteasome-binding surface of the PA26 heptamer. Activation
loops are yellow, C-terminal helix is red. View direction is
from below structure in a. d, Alignment of T. brucei PA26 and
human REG  amino-acid
sequences. Identical residues are shaded in pink. Disordered
residues are indicated with a thin line. PA26/REG residues
are structurally equivalent from the start of helix 2 to the C
terminus as indicated. The alignment for helix 1 is tentative.
The hexahistidine affinity tag inserted after the initiator
methionine of PA26 is shown. Every tenth residue is marked with
a dash (the first PA26 residue marked is Gln10). Residues that
contact the 20S proteasome are indicated with blue triangles.
The PA26 construct used in this study has a threonine in place
of the authentic serine^4 at position 226.
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