The long-term goal of this research program is to elucidate the molecular mechanisms underlying transducin signaling in rod and cone photoreceptors. Although a remarkable level of understanding of how transducin functions in the phototransduction cascade has been achieved, the mechanisms underlying the folding of transducin-? (G?t1) in rod photoreceptors (RPs) remains poorly understood. Defects in protein folding are a common cause of retinal degeneration and blindness; this underscores the need to investigate the folding mechanisms of key photoreceptor proteins including transducin. Evidence has emerged that the protein known as resistance to inhibitors of cholinesterase 8 homolog A (Ric8A) is a chaperone of G-protein ?-subunits of the G?i/o family, to which transducin belongs. Based on our finding that Ric8A is expressed in RPs, we hypothesize that Ric8A is a chaperone for newly synthesized and/or light-translocated G?t1. In order to elucidate the mechanism of Ric8A chaperone activity, we will investigate the structure and properties of the complex between G?t1 and Ric8A. The structure of the G?t1-Ric8A complex in solution will be determined by small angle X-ray scattering (SAXS), using atomic models of G?t1 and Ric8A as a framework, and distance constraints derived from cross-linking experiments. In parallel, X-ray crystallography will be used to determine high-resolution structures of Ric8A, alone and in complex with G?t1. Structural information on the G?t1-Ric8A complex will serve as a starting point for mutational and biochemical analyses of both the protein interface and the chaperone activity of Ric8A. We developed a mouse model in which Ric8A is knocked out specifically in RPs (Ric8AF/FCre+), and our preliminarily data support a role for Ric8A as a G?t1 chaperone. In parallel with the structural studies, we will investigate the functional significance of Ric8A in RPs by conducting comprehensive examination of this mouse model. In addition, we will examine the potential role of Ric8A as a chaperone of G?o in rod bipolar cells (RBCs). Elucidation of molecular details of G?t1 folding by Ric8A is expected to have important implications for retinal diseases and to deepen our understanding of the G-protein chaperone machinery more generally. A second major focus of the proposed research is on the mechanisms whereby synaptic transmission between RPs and RBCs is modulated by light- translocated transducin. Based on our initial finding of Cav1.4 Ca2+ channel activation by transducin-?? (G?1?1) in HEK293T cells, we hypothesize that G?1?1 modulates signaling at the RP-RBC synapse. The mechanisms underlying the modulation of RP output by G?1?1 will be investigated in biochemical and electrophysiological experiments using in vitro and in vivo approaches. The proposed analysis of synapse modulation by transducin is expected to cause a profound paradigm shift, expanding the role of transducin from the generation of visual signals to the modulation of the RP output.

Public Health Relevance

Transducin is the key molecule in the transfer of visual signals in the vertebrate rod and cone photoreceptors. We propose to investigate the mechanisms of transducin folding through analysis of its interaction with the putative chaperone Ric8A and to elucidate the mechanisms whereby light-translocated transducin modulates synaptic output of rod photoreceptors. These studies are directly relevant to understanding the molecular basis of human visual disorders, because in many cases these are caused by defective protein folding and dysregulation of synaptic signaling in the retina.

National Institute of Health (NIH)
National Eye Institute (NEI)
Research Project (R01)
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Special Emphasis Panel (ZRG1)
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Neuhold, Lisa
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University of Iowa
Schools of Medicine
Iowa City
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Kerov, Vasily; Laird, Joseph G; Joiner, Mei-Ling et al. (2018) ?2?-4 Is Required for the Molecular and Structural Organization of Rod and Cone Photoreceptor Synapses. J Neurosci 38:6145-6160
Pahlberg, Johan; Majumder, Anurima; Artemyev, Nikolai O (2018) Ex Vivo Functional Evaluation of Synaptic Transmission from Rods to Rod Bipolar Cells in Mice. Methods Mol Biol 1753:203-216
Yadav, Ravi P; Artemyev, Nikolai O (2017) AIPL1: A specialized chaperone for the phototransduction effector. Cell Signal 40:183-189
Cheguru, Pallavi; Majumder, Anurima; Yadav, Ravi et al. (2015) The solution structure of the transducin-?-uncoordinated 119 protein complex suggests occlusion of the G????-binding sites. FEBS J 282:550-61
Manes, Gaël; Cheguru, Pallavi; Majumder, Anurima et al. (2014) A truncated form of rod photoreceptor PDE6 ?-subunit causes autosomal dominant congenital stationary night blindness by interfering with the inhibitory activity of the ?-subunit. PLoS One 9:e95768
Kuburas, Adisa; Thompson, Stewart; Artemyev, Nikolai O et al. (2014) Photophobia and abnormally sustained pupil responses in a mouse model of bradyopsia. Invest Ophthalmol Vis Sci 55:6878-85
Majumder, Anurima; Pahlberg, Johan; Boyd, Kimberly K et al. (2013) Transducin translocation contributes to rod survival and enhances synaptic transmission from rods to rod bipolar cells. Proc Natl Acad Sci U S A 110:12468-73
Liu, Xiaoni; Kerov, Vasily; Haeseleer, Françoise et al. (2013) Dysregulation of Ca(v)1.4 channels disrupts the maturation of photoreceptor synaptic ribbons in congenital stationary night blindness type 2. Channels (Austin) 7:514-23
Majumder, Anurima; Gopalakrishna, Kota N; Cheguru, Pallavi et al. (2013) Interaction of aryl hydrocarbon receptor-interacting protein-like 1 with the farnesyl moiety. J Biol Chem 288:21320-8
Sinha, Satyabrata; Majumder, Anurima; Belcastro, Marycharmain et al. (2013) Expression and subcellular distribution of UNC119a, a protein partner of transducin ? subunit in rod photoreceptors. Cell Signal 25:341-8

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