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PDBsum entry 3k1r
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Structural protein
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PDB id
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3k1r
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References listed in PDB file
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Key reference
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Title
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The structure of the harmonin/sans complex reveals an unexpected interaction mode of the two usher syndrome proteins.
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Authors
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J.Yan,
L.Pan,
X.Chen,
L.Wu,
M.Zhang.
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Ref.
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Proc Natl Acad Sci U S A, 2010,
107,
4040-4045.
[DOI no: ]
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PubMed id
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Abstract
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The hereditary hearing-vision loss disease, Usher syndrome I (USH1), is caused
by defects in several proteins that can interact with each other in vitro.
Defects in USH1 proteins are thought to be responsible for the developmental and
functional impairments of sensory cells in the retina and inner ear.
Harmonin/USH1C and Sans/USH1G are two of the USH1 proteins that interact with
each other. Harmonin also binds to other USH1 proteins such as cadherin 23
(CDH23) and protocadherin 15 (PCDH15). However, the molecular basis governing
the harmonin and Sans interaction is largely unknown. Here, we report an
unexpected assembly mode between harmonin and Sans. We demonstrate that the
N-terminal domain and the first PDZ domain of harmonin are tethered by a
small-domain C-terminal to PDZ1 to form a structural and functional supramodule
responsible for binding to Sans. We discover that the SAM domain of Sans,
specifically, binds to the PDZ domain of harmonin, revealing previously unknown
interaction modes for both PDZ and SAM domains. We further show that the
synergistic PDZ1/SAM and PDZ1/carboxyl PDZ binding-motif interactions, between
harmonin and Sans, lock the two scaffold proteins into a highly stable complex.
Mutations in harmonin and Sans found in USH1 patients are shown to destabilize
the complex formation of the two proteins.
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Figure 1.
The multi-dentate interaction between harmonin and Sans. (A)
A schematic diagram showing the domain organizations of harmonin
and Sans. The NPDZ1 and SAM-PBM boundaries used in this study
are indicated. (B) GST-fusion protein-based pull-down assay
showing that NPDZ1 binds to the SAM domain alone and the SAM-PBM
of Sans. No interaction between the N-domain and the SAM domain
was detected. (C) Analytical gel-filtration analysis showing
that harmonin NPDZ1 and Sans SAM-PBM forms a 1∶1
stoichiometric complex. (D) ITC-based measurements of the
binding affinities of NPDZ1 with Sans PBM, SAM, and SAM-PBM.
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Figure 4.
Molecular details of the harmonin NPDZ1 and Sans SAM-PBM
interaction. (A and B) The combined surface charge
representation (NPDZ1) and the stick-ribbon model (SAM-PBM)
showing the interaction interface between harmonin NPDZ1 and
Sans SAM-PBM. The binding interface between the NPDZ1 and Sans
PBM is better viewed in (A), whereas the binding interface
between the NPDZ1 and Sans SAM is optimally depicted in (B). (C
and D) Stereo views showing the detailed interactions between
harmonin PDZ1 and Sans PBM (C), and between PDZ1 and Sans SAM
(D). The hydrogen bonds and salt bridges involved in the
interfaces are indicated as Dashed Lines. (E) A schematic
cartoon diagram summarizing the three different binding modes of
PDZ domains.
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