Article

An ARL3-UNC119-RP2 GTPase cycle targets myristoylated NPHP3 to the primary cilium

Genentech Inc., South San Francisco, California 94080, USA.
Genes & development (Impact Factor: 10.8). 11/2011; 25(22):2347-60. DOI: 10.1101/gad.173443.111
Source: PubMed

ABSTRACT

The membrane of the primary cilium is a highly specialized compartment that organizes proteins to achieve spatially ordered signaling. Disrupting ciliary organization leads to diseases called ciliopathies, with phenotypes ranging from retinal degeneration and cystic kidneys to neural tube defects. How proteins are selectively transported to and organized in the primary cilium remains unclear. Using a proteomic approach, we identified the ARL3 effector UNC119 as a binding partner of the myristoylated ciliopathy protein nephrocystin-3 (NPHP3). We mapped UNC119 binding to the N-terminal 200 residues of NPHP3 and found the interaction requires myristoylation. Creating directed mutants predicted from a structural model of the UNC119-myristate complex, we identified highly conserved phenylalanines within a hydrophobic β sandwich to be essential for myristate binding. Furthermore, we found that binding of ARL3-GTP serves to release myristoylated cargo from UNC119. Finally, we showed that ARL3, UNC119b (but not UNC119a), and the ARL3 GAP Retinitis Pigmentosa 2 (RP2) are required for NPHP3 ciliary targeting and that targeting requires UNC119b myristoyl-binding activity. Our results uncover a selective, membrane targeting GTPase cycle that delivers myristoylated proteins to the ciliary membrane and suggest that other myristoylated proteins may be similarly targeted to specialized membrane domains.

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    • "The highly conserved Arl3 À only present in ciliated organisms – localizes throughout the cell and is enriched in the primary cilium (Avidor- Reiss et al., 2004; Blacque et al., 2005; Zhou et al., 2006). While RP2 functions as an Arl3 GAP and is thus important for the import of lipidated cargo by recycling Arl3 and its effectors (Schwarz et al., 2012; Wright et al., 2011; Zhang et al., 2015), the guanine nucleotide exchange factor (GEF) that activates Arl3 remains unknown. We had anticipated that in order for Arl3 to mediate cargo release inside cilia, an Arl3-specific GEF should be localized there as well. "
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