Photoreceptor calcium sensor proteins in detergent-resistant membrane rafts are regulated via binding to caveolin-1
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01.07.2018 |
Vladimirov V.
Zernii E.
Baksheeva V.
Wimberg H.
Kazakov A.
Tikhomirova N.
Nemashkalova E.
Mitkevich V.
Zamyatnin A.
Lipkin V.
Philippov P.
Permyakov S.
Senin I.
Koch K.
Zinchenko D.
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Cell Calcium |
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5 |
Ссылка
© 2018 Elsevier Ltd Rod cell membranes contain cholesterol-rich detergent-resistant membrane (DRM) rafts, which accumulate visual cascade proteins as well as proteins involved in regulation of phototransduction such as rhodopsin kinase and guanylate cyclases. Caveolin-1 is the major integral component of DRMs, possessing scaffolding and regulatory activities towards various signaling proteins. In this study, photoreceptor Ca 2+ -binding proteins recoverin, NCS1, GCAP1, and GCAP2, belonging to neuronal calcium sensor (NCS) family, were recognized as novel caveolin-1 interacting partners. All four NCS proteins co-fractionate with caveolin-1 in DRMs, isolated from illuminated bovine rod outer segments. According to pull-down assay, surface plasmon resonance spectroscopy and isothermal titration calorimetry data, they are capable of high-affinity binding to either N-terminal fragment of caveolin-1 (1–101), or its short scaffolding domain (81–101) via a novel structural site. In recoverin this site is localized in C-terminal domain in proximity to the third EF-hand motif and composed of aromatic amino acids conserved among NCS proteins. Remarkably, the binding of NCS proteins to caveolin-1 occurs only in the absence of calcium, which is in agreement with higher accessibility of the caveolin-1 binding site in their Ca 2+ -free forms. Consistently, the presence of caveolin-1 produces no effect on regulatory activity of Ca 2+ -saturated recoverin or NCS1 towards rhodopsin kinase, but upregulates GCAP2, which potentiates guanylate cyclase activity being in Ca 2+ -free conformation. In addition, the interaction with caveolin-1 decreases cooperativity and augments affinity of Ca2 + binding to recoverin apparently by facilitating exposure of its myristoyl group. We suggest that at low calcium NCS proteins are compartmentalized in photoreceptor rafts via binding to caveolin-1, which may enhance their activity or ensure their faster responses on Ca 2+ -signals thereby maintaining efficient phototransduction recovery and light adaptation.
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