 |
PDBsum entry 3f8t
|
|
|
|
References listed in PDB file
|
 |
|
Key reference
|
|
|
Title
|
|
Insights into the architecture of the replicative helicase from the structure of an archaeal mcm homolog.
|
|
|
Authors
|
|
B.Bae,
Y.H.Chen,
A.Costa,
S.Onesti,
J.S.Brunzelle,
Y.Lin,
I.K.Cann,
S.K.Nair.
|
|
|
Ref.
|
|
Structure, 2009,
17,
211-222.
[DOI no: ]
|
|
|
PubMed id
|
|
|
|
|
|
Abstract
|
|
|
The minichromosome maintenance (MCM) proteins, members of the AAA+ (ATPase
associated with diverse cellular activities) superfamily, are believed to
constitute the replicative helicase in eukaryotic and archaeal species. Here, we
present the 1.9 A resolution crystal structure of a monomeric MCM homolog from
Methanopyrus kandleri, the first crystallographic structure of a full-length
MCM. We also present an 18 A cryo-electron microscopy reconstruction of the
hexameric MCM from Methanothermobacter thermautotrophicus, and fit the atomic
resolution crystal structure into the reconstruction in order to generate an
atomic model for the oligomeric assembly. These structural data reveal a
distinct active site topology consisting of a unique arrangement of critical
determinants. The structures also provide a molecular framework for
understanding the functional contributions of trans-acting elements that
facilitate intersubunit crosstalk in response to DNA binding and ATP hydrolysis.
|
|
|
|
|
|
|
|
Figure 3.
Figure 3. Cryo-EM Density Map of the MCM Hexamer
(A and
C) Surface rendering of the cryo-EM density map (displayed at
2σ) viewed from the top and the side, respectively. The side
view clearly shows the lateral holes, which are disrupted by an
isthmus of electron density.
(B and D) Fitting of the AAA+
domain from MkaMCM2 (red) and the N-terminal domain from MthMCM
(green, Fletcher et al., 2003). The AAA+ domain of MkaMCM2
matches well the dome-shaped electron density.
(E) A view
showing the fitting of two hybrid monomers (including the
N-terminal domain of MthMCM and the AAA+ domain of MkaMCM2). The
N-terminal domain of one subunit (highlighted in green)
communicates with the AAA+ domain of the next-neighboring
subunit (in red) through the interaction between the PS1BH of
the AAA+ domain (shown in yellow) and the β7-β8 loop of the
N-terminal domain of an adjacent subunit (in orange) consistent
with biochemical studies on MthMCM (Sakakibara et al., 2008).
(F) A close up of the same interaction.
|
|
Figure 4.
Figure 4. Unique Trans-Acting Residues Characterize the MCM
AAA+ Domain
(A) Model of the MCM hexamer derived as per
Figure 3B showing the location of the composite active site
formed between two AAA+ domains (colored in blue and red).
(B) A close up view of the composite active site showing
residues that have been demonstrated to be critical for ATP
hydrolysis. The composite active site in MCM has unique features
that distinguish the AAA+ modules of these proteins from
classical AAA+ ATPases such as DnaA.
(C) Within the active
site of DnaA (Erzberger et al., 2006), the Walker A and B
motifs, sensor I and sensor II helix, are situated in one
molecule as cis-acting elements, but the critical arginine
finger is a trans-acting residue that is contributed from a
neighboring subunit.
(D) In contrast, the sensor II helix
in MCM functions in trans and is contributed by a neighboring
subunit.
(E–H) This arrangement of trans-acting elements
is similar to that found in viral superfamily III helicases,
such as the papillomavirus E1 helicase (Enemark and Joshua-Tor,
2006) (E). An additional trans-site has been identified by
biochemical analysis of SsoMCM (Moreau et al., 2007) and
consists of a motif containing a highly conserved acidic residue
at the base of PS1BH. Comparison of the structure of the SV40
large T antigen bound to (F) ATP and (G) ADP demonstrates that
this acidic residue orients the arginine finger in response to
the nature of the nucleotide (Gai et al., 2004). Likewise, a
similar, highly conserved acidic residue is located as a
trans-element in MCM (H) where it might similarly affect
intersubunit association in response to nucleotide hydrolysis.
|
|
|
|
|
|
The above figures are
reprinted
by permission from Cell Press:
Structure
(2009,
17,
211-222)
copyright 2009.
|
|
|
|
|
|
|
