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Figure 3.
Figure 3. Structure of the BCL6 BTB Domain/SMRT-BBD
Complex(A) Ribbon diagram of the 2:2 complex. The
crystallographic asymmetric unit contains the entire four-chain
structure. The two chains of the BCL6 BTB domain dimer are
colored blue and red, and the two SMRT chains are colored yellow
and green. The N termini of the two SMRT chains are
labeled.(B–D) View of the BCL6 BTB domain displayed as a
solvent accessible surface colored according to the two chains
of the BTB dimer (blue and white), with the two SMRT fragments
rendered in stick representation (oxygens in red, nitrogens in
blue, and the carbons of the two corepressor chains colored in
either yellow or green, as in [A]). The two nonoverlapping
surfaces of the BCL6 BTB dimer that are buried upon peptide
binding are highlighted in purple. (B) View in same orientation
as in [A]. (C) “Bottom” of the complex, viewed along the
molecular pseudo-2-fold axis. (D) Ser-1424 (hidden by His-116 in
this view) and Ile-1425 of SMRT are buried in a groove formed
in part by Arg-13′ (α1′) and His-116 (α6) from the
two chains of the BCL6 BTB domain.(E) Sequence alignment of
selected human BTB/zinc finger proteins and the observed
secondary structure of the BCL6 BTB domain. The
residue-by-residue surfaces buried due to interactions with the
yellow SMRT peptide are indicated with red and blue bars (color
scheme according to [A]). HIC-1 has a 13 amino acid insert at
the position indicated by the three asterisks.
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