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Cellular/Molecular Transducin Translocation in Rods Is Triggered by Saturation
 

Summary: Cellular/Molecular
Transducin Translocation in Rods Is Triggered by Saturation
of the GTPase-Activating Complex
Ekaterina S. Lobanova,1 Stella Finkelstein,1 Hongman Song,2 Stephen H. Tsang,3 Ching-Kang Chen,4 Maxim Sokolov,5
Nikolai P. Skiba,1 and Vadim Y. Arshavsky1
1Albert Eye Research Institute, Duke University Medical Center, Durham, North Carolina 27710, 2Department of Biochemistry, West Virginia University
School of Medicine, Morgantown, West Virginia 26506, 3Brown Glaucoma Laboratory, Edward Harkness Eye Institute, Columbia University, New York,
New York 10032, 4Department of Biochemistry, Virginia Commonwealth University, Richmond, Virginia 23298, and 5Sensory Neuroscience Research
Center and West Virginia University Eye Institute, Morgantown, West Virginia 26506
LightcausesmassivetranslocationofG-proteintransducinfromthelight-sensitiveoutersegmentcompartmentoftherodphotoreceptor
cell. Remarkably, significant translocation is observed only when the light intensity exceeds a critical threshold level. We addressed the
natureofthisthresholdusingaseriesofmutantmiceandfoundthatthethresholdcanbeshiftedtoeitheralowerorhigherlightintensity,
dependent on whether the ability of the GTPase-activating complex to inactivate GTP-bound transducin is decreased or increased. We
also demonstrated that the threshold is not dependent on cellular signaling downstream from transducin. Finally, we showed that the
extentoftransducin subunittranslocationisaffectedbythehydrophobicityofitsacylmodification.Thisimpliesthatinteractionswith
membranes impose a limitation on transducin translocation. Our data suggest that transducin translocation is triggered when the cell
exhausts its capacity to activate transducin GTPase, and a portion of transducin remains active for a sufficient time to dissociate from
membranesandtoescapefromtheoutersegment.Overall,thethresholdmarkstheswitchoftherodfromthehighlylight-sensitivemode
of operation required under limited lighting conditions to the less-sensitive energy-saving mode beneficial in bright light, when vision is
dominated by cones.

  

Source: Arshavsky, Vadim Y. - Department of Pharmacology, Duke University
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Collections: Biology and Medicine