Fig. 2. ATXR5/6 contain a bipartite catalytic domain composed of nSET
and SET. (A) Ribbon representation of the RcATXR5-H3.1-AdoHcy ternary complex in which nSET and SET are highlighted in gray and green, respectively.
Carbon atoms of H3.1 and product cofactor are colored in orange and magenta,
respectively. (B) Zoomed view of the peptide binding cleft of RcATXR5. Three-letter code refers to H3.1 residues. Carbon atoms of residues found in the L1, L2,
and L3 loops are rendered in yellow, beige, and purple, respectively. The carbon
atoms of other residues interacting with H3.1 are highlighted in green. Carbon
atoms of H3.1 residues are colored in orange, whereas oxygen and nitrogen atoms
are highlighted in red and blue. Hydrogen bonds and water molecules are illustrated as red dashed lines and red spheres, respectively. (C) Simulated annealing
Fo – Fc omit map (green) contoured at 2s. The H3.1 peptide is rendered as in (A).
Fig. 3. The selectivity pocket
and safety belt of ATXR5/6-type
H3K27 methyltransferases are
responsible for H3.1 preference
over H3.3. (A) The structure of
the ATXR5-H3.1-SAH complex in
electrostatic potential surface representation, with the selectivity
pocket and safety belt highlighted.
Positive and negative potentials are
in blue and red, respectively. Inlet
figure shows a zoomed view of the
residues forming the surface of the
selectivity pocket (three-letter code
refers to histone H3.1 residues).
Hydrogen bonds are shown as dashed
red lines. (B) In vitro HKM assay
using recombinant chromatin containing plant H3.1 or H3.3 as substrates and WT or point mutants of
ATXR6 from A. thaliana. The enzymatic activity indicated for each
reaction is relative to the activity
of ATXR6 (WT) on H3.1 nucleosomes.
WT E186D E186S E186A M190A R309Q R309A Y339A
H3.1H3.3 H3.3 H3.1 H3.1 H3.1 H3.3 H3.3H3.1H3.3 H3.3 H3.1 H3.1 H3.1 H3.3 H3.3
100% 7% 24% 0% 1% 0% 0% 0% 87% 2% 2% 2% 98%22% 0% 0% B