51 research outputs found
A Compact Intermediate State of Calmodulin in the Process of Target Binding
Calmodulin undergoes characteristic conformational changes
by binding Ca<sup>2+</sup>, which allows it to bind to more than 300
target proteins and regulate numerous intracellular processes in all
eukaryotic cells. We measured the conformational changes of calmodulin
upon Ca<sup>2+</sup> and mastoparan binding using the time-resolved
small-angle X-ray scattering technique combined with flash photolysis
of caged calcium. This measurement system covers the time range of
0.5–180 ms. Within 10 ms of the stepwise increase in Ca<sup>2+</sup> concentration, we identified a distinct compact conformational
state with a drastically different molecular dimension. This process
is too fast to study with a conventional stopped-flow apparatus. The
compact conformational state was also observed without mastoparan,
indicating that the calmodulin forms a compact globular conformation
by itself upon Ca<sup>2+</sup> binding. This new conformational state
of calmodulin seems to regulate Ca<sup>2+</sup> binding and conformational
changes in the N-terminal domain. On the basis of this finding, an
allosteric mechanism, which may have implications in intracellular
signal transduction, is proposed
Images of a) porcine; b) ranine; c) murine; d) newt; e) piscine eyes in the sagittal plane.
<p>The position of the equatorial plane is marked with the blue arrow and the optic axis, along which the sagittal refractive index profiles were measured, is marked with a red arrow. The scale bars in the right hand lower corner are equal to a) 4 mm (porcine); b) 2 mm (ranine); c) 1 mm (murine); d) 0.5 mm (newt); e) 1 mm (piscine).</p
Refractive index profiles in the equatorial planes of three representative porcine (a),c) and e)) and three representative murine (b),d) and f)) lenses.
<p>Arrows point to discontinuities in the profiles.</p
Widths of equatorial and sagittal refractive index profiles and the proportions of each profile with refractive index equal to and above a given value in lenses from five species.
<p>Widths of equatorial and sagittal refractive index profiles and the proportions of each profile with refractive index equal to and above a given value in lenses from five species.</p
Pictorial representation of isoindicial contours of refractive index in a lens where the contours in the inner regions of the lens are wider in the sagittal than in the equatorial plane.
<p>Pictorial representation of isoindicial contours of refractive index in a lens where the contours in the inner regions of the lens are wider in the sagittal than in the equatorial plane.</p
Second order polynomial functions fitted to refractive index profiles in the equatorial planes of lenses from five species.
<p>Second order polynomial functions fitted to refractive index profiles in the equatorial planes of lenses from five species.</p
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