The Caenorhabditis elegans Kinesin-3 Motor UNC-104/KIF1A Is Degraded upon Loss of Specific Binding to Cargo

National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, India.
PLoS Genetics (Impact Factor: 7.53). 11/2010; 6(11):e1001200. DOI: 10.1371/journal.pgen.1001200
Source: PubMed


UNC-104/KIF1A is a Kinesin-3 motor that transports synaptic vesicles from the cell body towards the synapse by binding to PI(4,5)P(2) through its PH domain. The fate of the motor upon reaching the synapse is not known. We found that wild-type UNC-104 is degraded at synaptic regions through the ubiquitin pathway and is not retrogradely transported back to the cell body. As a possible means to regulate the motor, we tested the effect of cargo binding on UNC-104 levels. The unc-104(e1265) allele carries a point mutation (D1497N) in the PI(4,5)P(2) binding pocket of the PH domain, resulting in greatly reduced preferential binding to PI(4,5)P(2)in vitro and presence of very few motors on pre-synaptic vesicles in vivo. unc-104(e1265) animals have poor locomotion irrespective of in vivo PI(4,5)P(2) levels due to reduced anterograde transport. Moreover, they show highly reduced levels of UNC-104 in vivo. To confirm that loss of cargo binding specificity reduces motor levels, we isolated two intragenic suppressors with compensatory mutations within the PH domain. These show partial restoration of in vitro preferential PI(4,5)P(2) binding and presence of more motors on pre-synaptic vesicles in vivo. These animals show improved locomotion dependent on in vivo PI(4,5)P(2) levels, increased anterograde transport, and partial restoration of UNC-104 protein levels in vivo. For further proof, we mutated a conserved residue in one suppressor background. The PH domain in this triple mutant lacked in vitro PI(4,5)P(2) binding specificity, and the animals again showed locomotory defects and reduced motor levels. All allelic variants show increased UNC-104 levels upon blocking the ubiquitin pathway. These data show that inability to bind cargo can target motors for degradation. In view of the observed degradation of the motor in synaptic regions, this further suggests that UNC-104 may get degraded at synapses upon release of cargo.

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    • "(not significant) are comparisons of each strain to wild type. a decrease in anterograde velocity (Kumar et al. 2010; Maeder et al. 2014). Since the ce782 mutation is in the motor domain, which is on the opposite end of the protein from the cargo binding domain, it is possible that the ce782 mutation also indirectly affects dynein motor activity in these bidirectionally moving vesicles. "
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    Genetics 09/2015; 201(1):91-116. DOI:10.1534/genetics.115.177337 · 5.96 Impact Factor
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    • "Please cite this article in press as: Neumann and Hilliard, Loss of MEC-17 Leads to Microtubule Instability and Axonal Degeneration, Cell Reports (2014), tagged version of UNC-104/kinesin-3 (Kumar et al., 2010), one of the main motor molecules responsible for transport of synaptic vesicles to presynaptic loci (Hall and Hedgecock, 1991). Wildtype animals exhibited a consistent distribution of fluorescence in PLM, with a smooth increase in expression along the axon in a proximal-to-distal fashion, and pooling at the distal end and at presynaptic sites (Figure 3A). "
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    Cell Reports 12/2013; 6(1). DOI:10.1016/j.celrep.2013.12.004 · 8.36 Impact Factor
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    • "Nerve ligature experiments indicate that kinesin-3 motors are not recycled by cytoplasmic dynein-dependent transport as they do not accumulate on the distal side of the ligature [18]. In addition, a recent study in C. elegans suggested that the kinesin-3 motor UNC-104 is not retrogradely transported by cytoplasmic dynein [97]. However, these results appear to contradict previous work from the same group showing that mutations in various cytoplasmic dynein subunits caused an accumulation of UNC-104 at the ends of neuronal processes [98]. "
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