Dataset Information

GTP-binding of ARL-3 is activated by ARL-13 as a GEF and stabilized by UNC-119.

ABSTRACT: Primary cilia are sensory organelles indispensable for organogenesis and tissue pattern formation. Ciliopathy small GTPase ARLs are proposed as prominent ciliary switches, which when disrupted result in dysfunctional cilia, yet how ARLs are activated remain elusive. Here, we discover a novel small GTPase functional module, which contains ARL-3, ARL-13, and UNC-119, localizes near the poorly understood inversin (InV)-like compartment in C. elegans. ARL-13 acts synergistically with UNC-119, but antagonistically with ARL-3, in regulating ciliogenesis. We demonstrate that ARL-3 is a unique small GTPase with unusual high intrinsic GDP release but low intrinsic GTP binding rate. Importantly, ARL-13 acts as a nucleotide exchange factor (GEF) of ARL-3, while UNC-119 can stabilize the GTP binding of ARL-3. We further show that excess inactivated ARL-3 compromises ciliogenesis. The findings reveal a novel mechanism that one ciliopathy GTPase ARL-13, as a GEF, coordinates with UNC-119, which may act as a GTP-binding stabilizing factor, to properly activate another GTPase ARL-3 in cilia, a regulatory process indispensable for ciliogenesis.

SUBMITTER: Zhang Q

PROVIDER: S-EPMC4840320 | biostudies-literature | 2016 Apr

REPOSITORIES: biostudies-literature

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GTP-binding of ARL-3 is activated by ARL-13 as a GEF and stabilized by UNC-119.

Zhang Qing Q Li Yan Y Zhang Yuxia Y Torres Vicente E VE Harris Peter C PC Ling Kun K Hu Jinghua J

Scientific reports 20160422

Primary cilia are sensory organelles indispensable for organogenesis and tissue pattern formation. Ciliopathy small GTPase ARLs are proposed as prominent ciliary switches, which when disrupted result in dysfunctional cilia, yet how ARLs are activated remain elusive. Here, we discover a novel small GTPase functional module, which contains ARL-3, ARL-13, and UNC-119, localizes near the poorly understood inversin (InV)-like compartment in C. elegans. ARL-13 acts synergistically with UNC-119, but an ...[more]

PMID: 27102355

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Project description:Munc18-1/UNC-18 is believed to prime SNARE-mediated membrane fusion, yet the underlying mechanisms remain enigmatic. Here, we examine how potential gain-of-function mutations of Munc18-1/UNC-18 affect locomotory behavior and synaptic transmission, and how Munc18-1-mediated priming is related to Munc13-1/UNC-13 and Tomosyn/TOM-1, positive and negative SNARE regulators, respectively. We show that a Munc18-1(P335A)/UNC-18(P334A) mutation leads to significantly increased locomotory activity and acetylcholine release in Caenorhabditis elegans, as well as enhanced synaptic neurotransmission in cultured mammalian neurons. Importantly, similar to tom-1 null mutants, unc-18(P334A) mutants partially bypass the requirement of UNC-13. Moreover, unc-18(P334A) and tom-1 null mutations confer a strong synergy in suppressing the phenotypes of unc-13 mutants. Through biochemical experiments, we demonstrate that Munc18-1(P335A) exhibits enhanced activity in SNARE complex formation as well as in binding to the preformed SNARE complex, and partially bypasses the Munc13-1 requirement in liposome fusion assays. Our results indicate that Munc18-1/UNC-18 primes vesicle fusion downstream of Munc13-1/UNC-13 by templating SNARE complex assembly and acts antagonistically with Tomosyn/TOM-1.SIGNIFICANCE STATEMENT At presynaptic sites, SNARE-mediated membrane fusion is tightly regulated by several key proteins including Munc18/UNC-18, Munc13/UNC-13, and Tomosyn/TOM-1. However, how these proteins interact with each other to achieve the precise regulation of neurotransmitter release remains largely unclear. Using Caenorhabditis elegans as an in vivo model, we found that a gain-of-function mutant of UNC-18 increases locomotory activity and synaptic acetylcholine release, that it partially bypasses the requirement of UNC-13 for release, and that this bypass is synergistically augmented by the lack of TOM-1. We also elucidated the biochemical basis for the gain-of-function caused by this mutation. Thus, our study provides novel mechanistic insights into how Munc18/UNC-18 primes synaptic vesicle release and how this protein interacts functionally with Munc13/UNC-13 and Tomosyn/TOM-1.

Dataset Information

GTP-binding of ARL-3 is activated by ARL-13 as a GEF and stabilized by UNC-119.

Publications

GTP-binding of ARL-3 is activated by ARL-13 as a GEF and stabilized by UNC-119.

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