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

Kannan Alpadi,Venkat Giri Magupalli,Stefanie Käppel,Louise Köblitz,Karin Schwarz,Gail M Seigel,Ching-Hwa Sung,Frank Schmitz

doi:10.1074/jbc.m801625200

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/delta 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/delta homology domain of Munc119 is essential for the interaction with the NADH binding region of RIBEYE(B) domain. But RIBEYE-Munc119 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.

Highlights

Munc119 is a mammalian ortholog of the Caenorhabditis elegans protein unc119 and essential for normal vision and synaptic transmission at photoreceptor synapses [1,2,3]
One clone encoded full-length Munc119, the two other clones encoded truncated Munc119 proteins that started at lysine (Lys-92) and isoleucine (Ile-93), shortly after the beginning of the PrBP/␦-homology domain of Munc119 (Fig. 1A), suggesting that the PrBP/␦ domain of Munc119 is probably responsible for the interaction
The final pellet was boiled with SDS loading buffer and sub- NADH binding subdomain of RIBEYE(B) domain (NBD) is jected to SDS-PAGE followed by Western blotting with the mediating the interaction with Munc119

Summary

Introduction

Munc119 ( denoted as RG4, Ref. 1) is a mammalian ortholog of the Caenorhabditis elegans protein unc119 and essential for normal vision and synaptic transmission at photoreceptor synapses [1,2,3]. The essential function of Munc119 for synaptic transmission at photoreceptor synapses and for vision has been demonstrated in a cone rod dystrophy patient with a premature termination codon mutation [5]. This termination codon mutation resulted in a Munc119 protein that lacked the PrBP/␦ domain. To better understand the physiological role and molecular composition of synaptic ribbons, we performed a YTH screen using the RIBEYE (B) domain as a bait. In this screen, we identified Munc119 as a potential RIBEYE-interacting protein

Methods

Results

Conclusion