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PDBsum entry 2ix7
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Contractile protein/metal binding
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PDB id
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2ix7
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References listed in PDB file
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Key reference
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Title
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Crystal structure of apo-Calmodulin bound to the first two iq motifs of myosin V reveals essential recognition features.
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Authors
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A.Houdusse,
J.F.Gaucher,
E.Krementsova,
S.Mui,
K.M.Trybus,
C.Cohen.
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Ref.
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Proc Natl Acad Sci U S A, 2006,
103,
19326-19331.
[DOI no: ]
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PubMed id
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Abstract
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A 2.5-A resolution structure of calcium-free calmodulin (CaM) bound to the first
two IQ motifs of the murine myosin V heavy chain reveals an unusual CaM
conformation. The C-terminal lobe of each CaM adopts a semi-open conformation
that grips the first part of the IQ motif (IQxxxR), whereas the N-terminal lobe
adopts a closed conformation that interacts more weakly with the second part of
the motif (GxxxR). Variable residues in the IQ motif play a critical role in
determining the precise structure of the bound CaM, such that even the consensus
residues of different motifs show unique interactions with CaM. This complex
serves as a model for the lever arm region of many classes of unconventional
myosins, as well as other IQ motif-containing proteins such as neuromodulin and
IQGAPs.
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Figure 1.
Fig. 1. Structure of the myosin V 2IQ complex. Two CaMs
bound in tandem to the two IQ motifs (gray helix) derived from
the sequence adjacent to the motor domain of murine myosin V are
shown. Consensus sequence residues (*) of the IQ motif are shown
in ball and stick. The helices of CaM, designated A–H, are
colored in pairs (AB in green, CD in yellow, EF in red, GH in
cyan). The orientation of the IQ motifs and CaM are
antiparallel. The interlobe linker 2 (purple) joins the N- and
C-terminal lobes. Linker 1 (pink, between the B and C helices)
and linker 3 (blue, between the F and G helices) interact with
consensus residues of the IQ motif. (Inset) A cartoon of the
myosin V molecule and the region that was crystallized (red box).
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Figure 2.
Fig. 2. Conserved features of the CaM / IQ motif
recognition. CaM bound to each IQ motif adopts a semi-open
C-lobe, and a closed N-lobe. The ribbon diagrams represent CaM
(color-coded as in Fig. 1) bound to the first IQ motif in two
orthogonal views about the y axis. Major interactions with the
semi-open C-terminal lobe are: consensus residues Gln-774 and
Arg-778 (green) form five hydrogen bonds with main chain atoms
in linker 3 (blue), whereas apolar side chains (Ile-773, yellow;
Ile-777, purple; Trp-780, black and pink) interact within the
hydrophobic C-lobe. Consensus residues Gly-779 (orange ball) and
Arg-783 (cyan), as well as Tyr-786 (yellow) interact with the
surface of the N-lobe composed of linker 1 (pink) and helix A.
Hydrogen bonds between Glu-114 in linker 3 of the C-lobe, and
the main-chain nitrogen of Glu-45 and Ala-46 in the N-lobe,
provide a sensing mechanism between the two halves of CaM.
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