Structural studies of 14-3-3/phosducin complex
M. Kacirova1,2, L. Rezabkova1,2,
P. Herman3, J. Vecer3, M. Sulc4, T. Obsil1,2
1Faculty of Science,Charles
University in Prague, 12843 Prague, Czech Republic
2Institute of Physiology, Academy of Sciences of the Czech Republic,
14220 Prague 4, Czech Republic
3Faculty of Mathematics and Physics, Inst. Physics, Charles University in
Prague; 12116 Prague, Czech Republic
4Institute of Microbiology, Academy of Sciences of the Czech Republic;
14220 Prague, Czech Republic
mirkakacirova@seznam.cz
Phosducin (Pd) is an important
protein, which is involved in eyesight sense biochemistry. It regulates perception
of sensitivity of light. Pd is expressed in photoreceptors, especially in rods,
but it is found in pineal gland and other tissues as well. It is involved in
G-protein signaling that allows sight [1, 2].
Dephosphorylation of Pd is induced by light and
causes its binding to Gβγ complex. The transport of the resulting Pd/Gβγ complex from the outer rod disk membrane then
induces the decrease in G-protein signaling. Therefore, the dephosphorylation
of Pd protects the signaling pathway against saturation in the presence of very
intense light. In the dark-adapted retina Pd is predominantly fosforylated at Ser54 and Ser73 [3]. Phosforylated
Pd doesn´t bind Gβγ but binds multifunctional 14-3-3 protein. This
interaction increases the G-protein signaling and thus the sensitivity towards
the light [4].
14-3-3 proteins are family of acidic
regulatory proteins that are expressed in all eukaryotic cells. They bind to
other proteins in a phosphorylation-dependent manner and affects
the structure of their binding partners [5]. Interaction between 14-3-3 and
phosphorylated Pd probably enables sequestering Pd from Gβγ subunit
or protecting phosphorylated Pd from degradation [2].
To elucidate the mechanism of 14-3-3-dependent
regulation of Pd function, we performed several biophysical studies of Pd/14-3-3
complex. We have prepared Pd/14-3-3ζ complex in vitro. Nondenaturating electrophoresis
was used to verify that the formation of Pd/14-3-3 complex is phosphorylation
dependent. Analytical ultracentrifugation was used to estimate the complex stoichiometry.
Conformational changes of Pd, induced by 14-3-3 protein binding, were studied using
fluorescence spectroscopy techniques.
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This work was funded
by Grant P305/11/0708 of the Czech Science Foundation, by Research Project
MSM0021620857 and Centre of Neurosciences LC554 of the Ministry of Education,
Youth, and Sports of the Czech Republic, by Grant 28510 of the Grant Agency of
the Charles University and by Research Project AV0Z50110509 of the Academy of
Sciences of the Czech Republic.