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: 12.64). 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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Available from: Diane C Slusarski, Aug 26, 2015
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    • "Humbert et al. (2012) reported the involvement of another ARL family small GTPase, ARL13B, in the INPP5E ciliary targeting network. The authors suggest that ARL13B releases INPP5E from PDE6D by binding to INPP5E rather than PDE6D, which differs from the cargo-release mechanism described biochemically and structurally used by ARL3 for both PDE6D and UNC119B [Ismail et al., 2011, 2012; Wright et al., 2011]. It will be of interest to further determine the role of ARL13B in PDE6D-dependent protein targeting. "
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    • "A key aspect is the role of the small GTPase Arl3 in targeting myristoylated and prenylated proteins, such as NPHP3, to the primary cilium via UNC119 and PDE6D effectors. Some of this work has already been published (Wright et al., 2011). We thank all the speakers for their participation and contributions and the discussion participants for making this Minisymposium such a great event. "
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    • "Both Arl2 and Arl3 have in addition to the N-terminal amphipathic helix a totally conserved glycine in position 2 however they are apparently not myirstoylated (Bologna et al, 2004). Although not much is known about membrane interactions of Arl2 and Arl3 a recent study has shown that the constitutively active Arl3 fractionates to both soluble and membranes fractions which is most likely due to the week affinity to membranes (Wright et al, 2011). "
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