 |
PDBsum entry 1m2f
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Circadian clock protein
|
PDB id
|
|
|
|
1m2f
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
References listed in PDB file
|
|
|
Key reference
|
|
|
Title
|
|
Structure and function from the circadian clock protein kaia of synechococcus elongatus: a potential clock input mechanism.
|
|
|
Authors
|
|
S.B.Williams,
I.Vakonakis,
S.S.Golden,
A.C.Liwang.
|
|
|
Ref.
|
|
Proc Natl Acad Sci U S A, 2002,
99,
15357-15362.
[DOI no: ]
|
|
|
PubMed id
|
|
|
|
|
|
Abstract
|
|
|
In the cyanobacterium Synechococcus elongatus (PCC 7942) the proteins KaiA,
KaiB, and KaiC are required for circadian clock function. We deduced a circadian
clock function for KaiA from a combination of biochemical and structural data.
Both KaiA and its isolated carboxyl-terminal domain (KaiA180C) stimulated KaiC
autophosphorylation and facilitated attenuation of KaiC autophosphorylation by
KaiB. An amino-terminal domain (KaiA135N) had no function in the
autophosphorylation assay. NMR structure determination showed that KaiA135N is a
pseudo-receiver domain. We propose that this pseudo-receiver is a timing
input-device that regulates KaiA stimulation of KaiC autophosphorylation, which
in turn is essential for circadian timekeeping.
|
|
|
|
|
|
|
|
Figure 3.
Fig 3. The solution structure of KaiA135N and comparisons
to other receiver domain proteins.  -strands are in blue,
 -helices are in purple,
and the flexible loop of KaiA135N and the equivalent region of
other receiver domains are in gold. The structure coordinates
have been deposited in the Protein Data Bank under PDB ID codes
1M2E and 1M2F for the average minimized structure and the family
of structures, respectively. (Ai) Schematic representation of
the average minimized structure. The solution structure of
KaiA135N is an - - sandwich built around a
five-parallel-strand -sheet with b-a-c-d-e
arrangement. The rotational correlation time (  [c]) was
calculated to be  8.2 ns, which is
consistent with a monomer in solution (21). (Aii) Stereoview of
the overlaid backbone of a family of 25 low-energy structures
calculated from 2,034 distance and geometry restraints. The
backbone rms deviation from the average is 0.38 ± 0.04
Å for residues 4-83 and 98-135. The rms deviation for all
heavy atoms is 0.78 ± 0.05 Å for the same residues.
Few medium- or long-range NOE contacts were identified for
residues 83-97, and 15N dynamics (see supporting information)
showed that this region is highly dynamic. (B) Structural
comparison of KaiA135N with other receiver domains. Shown here
are KaiA135N (Bi), the NtrC (1DC7) receiver domain (Bii), and
the AmiR (1QO0 [PDB]
, residues 11-131) receiver domain (Biii) at two mutually
orthogonal views. Figures were prepared with SPOCK (38).
|
|
Figure 5.
Fig 5. Working model of KaiA protein function and its role
in S. elongatus circadian timekeeping. CikA and other
environmental sensors initiate signal transduction cascades that
result in activation of the KaiA pseudo-receiver domain. This
activation modulates the KaiA carboxyl-terminal domain's
enhancement of the KaiC autophosphorylation rate. Thus,
equilibria between KaiC phosphorylation states are perturbed.
These states differentially control clock output, possibly
through the SasA protein kinase. In this manner, a cycle of
input, oscillation, and output can be established.
|
|
|
|
|
|
|
|
|
|
