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Interaction of transducin with uncoordinated 119 protein (UNC119): implications for the model of transducin trafficking in rod photoreceptors
Journal article   Open access   Peer reviewed

Interaction of transducin with uncoordinated 119 protein (UNC119): implications for the model of transducin trafficking in rod photoreceptors

Kota N Gopalakrishna, Krishnarao Doddapuneni, Kimberly K Boyd, Ikuo Masuho, Kirill A Martemyanov and Nikolai O Artemyev
The Journal of biological chemistry, Vol.286(33), pp.28954-28962
08/19/2011
DOI: 10.1074/jbc.M111.268821
PMCID: PMC3190703
PMID: 21712387
url
https://doi.org/10.1074/jbc.M111.268821View
Published (Version of record) Open Access

Abstract

The key visual G protein, transducin undergoes bi-directional translocations between the outer segment (OS) and inner compartments of rod photoreceptors in a light-dependent manner thereby contributing to adaptation and neuroprotection of rods. A mammalian uncoordinated 119 protein (UNC119), also known as Retina Gene 4 protein (RG4), has been recently implicated in transducin transport to the OS in the dark through its interaction with the N-acylated GTP-bound transducin-α subunit (Gα(t1)). Here, we demonstrate that the interaction of human UNC119 (HRG4) with transducin is dependent on the N-acylation, but does not require the GTP-bound form of Gα(t1). The lipid specificity of UNC119 is unique: UNC119 bound the myristoylated N terminus of Gα(t1) with much higher affinity than a prenylated substrate, whereas the homologous prenyl-binding protein PrBP/δ did not interact with the myristoylated peptide. UNC119 was capable of interacting with Gα(t1)GDP as well as with heterotrimeric transducin (G(t)). This interaction of UNC119 with G(t) led to displacement of Gβ(1)γ(1) from the heterotrimer. Furthermore, UNC119 facilitated solubilization of G(t) from dark-adapted rod OS membranes. Consistent with these observations, UNC119 inhibited rhodopsin-dependent activation of G(t), but had no effect on the GTP-hydrolysis by Gα(t1). A model for the role of UNC119 in the IS→OS translocation of G(t) is proposed based on the UNC119 ability to dissociate G(t) subunits from each other and the membrane. We also found that UNC119 inhibited activation of G(o) by D2 dopamine receptor in cultured cells. Thus, UNC119 may play conserved inhibitory role in regulation of GPCR-G protein signaling in non-visual tissues.
 Transducin - genetics Receptors, Dopamine - metabolism Humans Heterotrimeric GTP-Binding Proteins - metabolism Protein Transport - physiology Cell Membrane - genetics Retinal Rod Photoreceptor Cells - metabolism Heterotrimeric GTP-Binding Proteins - genetics Animals Cattle Models, Biological Retinal Rod Photoreceptor Cells - cytology Adaptor Proteins, Signal Transducing - genetics Signal Transduction - physiology Transducin - metabolism Cell Membrane - metabolism Adaptor Proteins, Signal Transducing - metabolism Receptors, Dopamine - genetics

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