Basis for Complex Formation of GCN5 Histone Acetyltransferase with H3
Harry Hurley '14 with
GCN5 Histone Acetyltransferase (HAT)
is a histone-modifying protein found in Tetrahymena thermophilia.
Acetyltransferases such as this one are crucial to successful
transcription. DNA in chromatin is bound about Histones, and HAT is
principal enzyme to signal Histone release. It does this
acetylation; acetylated Histone tails have a higher affinity for FACT,
which will cause the Histone to come apart, allowing RNA polymerase to
transcribe the gene.
GCN5 targets the
Carboxy-terminal end of the
phosphorylated Ser10 on H3 has shown to
raise the affinity
GCN5 binding. GCN5 can transfer an acetyl group from a
the carboxy-terminal tail on H3. This increases the
affinity for FACT binding and activity, ultimately allowing
transcription to proceed along the gene previously bound by the
is a monomer of roughly 22,000 molecular weight, composed of
a 162 peptide long polypeptide chain. GCN5
is a globular protein made up of five α-helices
and a six-stranded β-sheet.
combine to form a
domain with a pronounced L-shaped cleft. The interaction
the H3 substrate is within the longer segment of the cleft, defined by
GCN5 and the
GCN5 monomer forms a
complex with acetyl CoA, which donates the acetyl group, and a 19
peptide carboxy terminal domain
of the H3 histone subunit.
the H3 chain is
responsible for accepting the acetyl group.
to the active site
is mediated by the
a both the
acetylator and the stabilizing factor for the H3 peptide.
Since it is so crucial to these aspects, GCN5 activity, it
must bind before
anything else does. The CoA - Protein interactions
H3 peptide ternary complex are made by the β4-turn-α3
the GCN5 domain
group and pantetheine arm of CoA. Additional interactions are
provided by the α1
helix of the N-terminal protein segment,
and the β4-strand
and the α4-turn
regions in the
and the β5-turn-α4
key factor to the binding
of H3 is
a phosphorylated Ser10
residue on H3.
extensive interactions between Thr11
and the GCN5
residues at the base of the
is dependent on
residue. The Thr11
side chain from H3 is buried
deeply in the base of the cleft, making substantial van der Waals
interactions with the
Thr11 also forms a hydrogen bond with Glu122. Here
is the full H3 polypeptide,
not included in the PDB.
Acetylation of the Lys14
residue hinges upon the proper K14-G15-L16-G17
bind to the GCN5
properly. The highly reactive Lys14 residue of the histone H3
peptide is directly anchored to the substrate binding site by van der
123 and Leu 126
in the β4
sheet at the
base of the peptide cleft and by the CoA cofactor, and
by hydrogen bonds to the backbone carbonyl group of Ala124,and
of CoA. The region of the
β4 strand that
interacts with the Lys14 residue of the histone H3 peptide has
which appears to be
essential to facilitate
these protein-substrate interactions as well as to point the backbone
carbonyls of residues Val 123 and Ala124 into the histone-binding cleft
to facilitate an electrostatic attraction for the lysine substrate.
novel observation of this structure is that
the phosphorylated histone H3 undergoes a significant
rearrangement when compared to the nonphosphorylated histone (Clements
et al., 2003).
result is a change in the overall architecture of the ternary GCN5
complex, promoting more interactions between GCN5 and the histone H3
substrate (Clements et al., 2003). In particular, the
interaction surface for the
N-terminus has moved significantly from the GCN5 α2 helix
unmodified H3 peptide to the α5-β6 loop in the case
phosphorylated H3 peptide (Clements et al., 2003). No
parallel has been found among
comparable histone acetyltransferases of this phosphorylated region.
Phospho-Ser10 enhancement of HAT activity is GCN5 specific,
rather than generally applicable to all histone acetyltransferases
(Rojas et al., 1999).
A., Poux, A., Lo, W.,
Pillus, L., Berger, S., Marmorstein, R. August 2003.
Basis for Histone and Phosphohistone Binding by the GCN5 Histone
Cell, Vol. 12, 461-473.
Poux, A., Cebrat, M., Kim, C., Cole, P., Marmorstein, R. October 2002.
Structure of the GCN5 histone cetyltransferase bound to a
bisubstrate inhibitor. PNAS,
Vol. 99 no. 22 14065-14070.
Poux, A., and Marmorstein, R. September, 2003.
Molecular Basis for GCN5/PCAF Histone Acetyltransferase
Selectivity for Histone and Nonhistone Substrates. Biochemistry, Vol.
Rojas, J., Trievel, R., Zhou, J., Mo, Y., Li, X., Berger, S., Allis,
D., Marmorstein, R. September 1999. Structure of Tetrahymena GCN5
Bound to Coenzyme A and a Histone H3 Peptide. Nature,
Vol 401, 93-98.