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Figure 3.
Figure 3. Intramolecular Interfaces in Monomeric
GCaMP2•Ca^2+
(A) Interfaces among the cpEGFP, M13, and
CaM modules in the structure of monomeric GCaMP2ΔRSET•Ca^2+.
Residues of the M13-cpEGFP module interacting with CaM are
colored red. Interfacial residues on CaM are colored in green
and blue for contacts with cpEGFP and the M13 helix,
respectively. A top view, rotated 90° around the horizontal
axis with respect to the view shown above, is shown as a cutaway
rendition of the surface (bottom-left). The fluorophores of
cpEGFP and Arg-377 of CaM are shown in stick presentation.
Surface presentation of the isolated CaM domain and M13-cpEGFP
unit were rotated by +90° and −90°, respectively, with
respect to the view of the assembled structure (top-left).
(B) Electrostatic potential of the M13-cpEGFP module and CaM
mapped onto its molecular surface. Views are identical to (A).
Red represents negative and blue represents positive potential
(−5 to +5 k[B]T).
(C) Schematic diagram of the
fluorophore environment and the hydrogen bond network between
cpEGFP and CaM. The numbering scheme for GCaMP2 was used.
Corresponding residue numbers in GFP are shown in brackets.
Carbon atoms of residues in cpEGFP, CaM, and linker segments are
shown in green, dark red, and gray, respectively. Hydrogen bonds
shown in the figure are between 2.7 and 3.3 Å (not drawn
to scale).
(D) Close-up views of the interfacial regions in
GCaMP2ΔRSET•Ca^2+. Water-mediated interaction between the
fluorophore and Arg-377 of the CaM domain (top) and cpEGFP:CaM
interfacial residues (bottom) are shown.
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