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Figure 2.
Overall view of the SifA-SKIP(PH) complex. A, ribbon diagram
of the SifA-SKIP(PH) complex, viewed in two orientations rotated
by 90°. The SifA N- (residues 21–136) and C-terminal
(residues 137–328) are shown in yellow and orange,
respectively, and the SKIP(PH) (residues 772–876) is in green.
The SifA conserved motifs WE(I/M)XXFF, which is important for
translocation (13), and WXXXE, which has been proposed to mimic
activated GTPase (16), are highlighted in pink and cyan,
respectively. The Leu^130 position buried at the complex
interface is displayed in red. B, molecular surface of the
complex (left), color-coded, and oriented as in the left view of
panel A, with the surface buried at the complex interface shown
in green. Close-up view (right) of key residues involved in the
binding interface. C, mapping sequence conservation in the SifB
homolog onto the molecular surface of SifA (yellow and orange
for the N- and C-terminal domain), oriented as in the left view
of panel A, with non-conserved side chains from the N- and
C-terminal domain shown in pink and magenta, respectively. Small
patches of non-conserved surface regions (pink) are located in
the N-terminal domain and within the binding interface (green)
while large patches of non-conserved surface regions (magenta)
are clustered within the C-terminal domain. D, surface
electrostatic potential map of SifA, oriented as in the right
view of panel A, showing a dominant electronegative potential
except for a large patch of electropositive potential clustered
near the translocation motif in the N-terminal domain.
Electrostatic surface potentials are contoured at −3/+3 kT/e
electrostatic units (k, Boltzmann constant; T, temperature in
Kelvin; e, electronic charge), where red describes a negative
and blue a positive potential. The figures were generated with
PyMOL (DeLano Scientific (2004), San Carlos, CA), and panel D
was generated with the APBS plug-in for PyMOL.
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