RIBEYE Recruits Munc119, a Mammalian Ortholog of the Caenorhabditis elegans Protein unc119, to Synaptic Ribbons of Photoreceptor Synapses

Abstract

Munc119 (also denoted as RG4) is a mammalian ortholog of the Caenorhabditis elegans protein unc119 and is essential for vision and synaptic transmission at photoreceptor ribbon synapses by unknown molecular mechanisms. Munc119/RG4 is related to the prenyl-binding protein PrBP/␦ and expressed at high levels in photoreceptor ribbon synapses. Synaptic ribbons are presynaptic specializations in the active zone of these tonically active synapses and contain RIBEYE as a unique and major component. In the present study, we identified Munc119 as a RIBEYE-interacting protein at photoreceptor ribbon synapses using five independent approaches. The PrBP/␦ homology domain of Munc119 is essential for the interaction with the NADH binding region of RIBEYE(B) domain. But RIBEYEMunc119 interaction does not depend on NADH binding. A RIBEYE point mutant (RE(B)E844Q) that no longer interacted with Munc119 still bound NADH, arguing that binding of Munc119 and NADH to RIBEYE are independent from each other. Our data indicate that Munc119 is a synaptic ribbon-associated component. We show that Munc119 can be recruited to synaptic ribbons via its interaction with RIBEYE. Our data suggest that the RIBEYE-Munc119 interaction is essential for synaptic transmission at the photoreceptor ribbon synapse.Munc119 (also denoted as RG4, Ref.

The Synaptic Ribbon Is a Site of Phosphatidic Acid Generation in Ribbon Synapses

“…7E,F). As shown previously, RIBEYE(B) binds NAD(H) (Schmitz et al, 2000;Alpadi et al, 2008;Magupalli et al, 2008) and shows an NADH-dependent FRET effect at about 427 nm Magupalli et al, 2008) (Fig. 7A).…”

“…Transfection of COS cells, expression and purification of bacterial fusion proteins, and purification of synaptic ribbons were performed as described previously (Schmitz et al, 1996(Schmitz et al, , 2000Alpadi et al, 2008;Magupalli et al, 2008). Statistical analyses were performed with Student's t tests.…”

“…Fluorescence microscopy was performed as described previously (Schmitz et al, 2000;Alpadi et al, 2008;Magupalli et al, 2008;Venkatesan et al, 2010) using an Axiovert200M microscope (Zeiss) or A1R confocal microscope (Nikon) as indicated.…”

Congenital stationary night blindness: An analysis and update of genotype–phenotype correlations and pathogenic mechanisms

“…With respect to its inhibitory effect on CDI, CABP4 and CTM seem functionally equivalent. Other proteins such as UNC119 and RIBEYE/CTBP2, for which proteineprotein interactions have been individually shown may link Cav1.4 channels to the synaptic ribbon as suggested by Schmitz and co-workers (Alpadi et al, 2008;Haeseleer, 2008;Schmitz et al, 2012) (Fig. 14), but are not implicated in CSNB.…”

Transducin translocation contributes to rod survival and enhances synaptic transmission from rods to rod bipolar cells

“…Thus, the light-induced decrease in intracellular Ca 2+ in the rod spherule might augment the inhibitory action of Gβ 1 γ 1 on the SNARE proteins and facilitate the reduction in glutamate release. An alternative mechanism for transducin's synaptic sensitization may involve a direct action of Gα t1 with UNC119, a partner for the synaptic ribbon protein RIBEYE (42). The exact mechanisms of transducin modulation of rod-to-rod bipolar cell signal transmission will require additional investigation.…”