7ok7
Crystal structure of the UNC119B ARL3 complex
Structural highlights
FunctionARL3_MOUSE Small GTP-binding protein which cycles between an inactive GDP-bound and an active GTP-bound form, and the rate of cycling is regulated by guanine nucleotide exchange factors (GEF) and GTPase-activating proteins (GAP). Required for normal cytokinesis and cilia signaling. Required for targeting proteins such as NPHP3 to the ciliary membrane by releasing myristoylated NPHP3 from UNC119B cargo adapter into the cilium (By similarity). Requires assistance from GTPase-activating proteins (GAPs) like RP2 and PDE6D, in order to cycle between inactive GDP-bound and active GTP-bound forms.[1] [2] Publication Abstract from PubMedTwo paralogs of the guanine dissociation inhibitor-like solubilizing factors UNC119, UNC119A and UNC119B, are present in the human genome. UNC119 binds to N-myristoylated proteins and masks the hydrophobic lipid from the hydrophilic cytosol, facilitating trafficking between different membranes. Two classes of UNC119 cargo proteins have been classified: low affinity cargoes, released by the Arf-like proteins ARL2 and ARL3, and high affinity cargoes, which are specifically released by ARL3 and trafficked to either the primary cilium or the immunological synapse. The UNC119 homologues have reported differences in functionality, but the structural and biochemical bases for these differences are unknown. Using myristoylated peptide binding and release assays, we show that peptides sharing the previously identified UNC119A high affinity motif show significant variations of binding affinities to UNC119B of up to 427-fold. Furthermore, we solve the first two crystal structures of UNC119B, one in complex with the high affinity cargo peptide of LCK and a second one in complex with the release factor ARL3. Using these novel structures, we identify a stretch of negatively charged amino acids unique to UNC119B that may undergo a conformational change following binding of a release factor which we propose as an additional release mechanism specific to UNC119B. The Structural and Biochemical Characterization of UNC119B Cargo Binding and Release Mechanisms.,Yelland T, Garcia E, Samarakoon Y, Ismail S Biochemistry. 2021 Jun 15;60(25):1952-63. doi: 10.1021/acs.biochem.1c00251. PMID:34130453[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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