| Structural highlights
Function
[LGR5_HUMAN] Orphan receptor. Stem cell marker of the intestinal epithelium and the hair follicle. Target gene of Wnt signaling. [ZNRF3_MOUSE] E3 ubiquitin-protein ligase that acts as a negative regulator of the Wnt signaling pathway by mediating the ubiquitination and subsequent degradation of Wnt receptor complex components Frizzled and LRP6. Acts on both canonical and non-canonical Wnt signaling pathway. Acts as a tumor suppressor in the intestinal stem cell zone by inhibiting the Wnt signaling pathway, thereby resticting the size of the intestinal stem cell zone.[1] [2] [RSPO2_MOUSE] Activator of the canonical Wnt signaling pathway by acting as a ligand for LGR4-6 receptors. Upon binding to LGR4-6 (LGR4, LGR5 or LGR6), LGR4-6 associate with phosphorylated LRP6 and frizzled receptors that are activated by extracellular Wnt receptors, triggering the canonical Wnt signaling pathway to increase expression of target genes. Also regulates the canonical Wnt/beta-catenin-dependent pathway and non-canonical Wnt signaling by acting as an inhibitor of ZNRF3, an important regulator of the Wnt signaling pathway. Probably also acts as a ligand for frizzled and LRP receptors.[3]
Publication Abstract from PubMed
The four secreted R-spondin (Rspo1-4) proteins of vertebrates function as stem cell growth factors and potentiate canonical Wnt signalling. Rspo proteins act by cross-linking members of two cell surface receptor families, complexing the stem cell markers LGR4-6 with the Frizzled-specific E3 ubiquitin ligases ZNRF3/RNF43. The consequent internalisation of the ternary LGR-Rspo-E3 complex removes the E3 ligase activity, which otherwise targets the Wnt receptor Frizzled for degradation, and thus enhances Wnt signalling. Multiple combinations of LGR4-6, Rspo1-4 and ZNRF3/RNF43 are possible, implying the existence of generic interaction determinants, but also of specific differences in complex architecture and activity. We present here a high resolution crystal structure of an ectodomain variant of human LGR5 (hLGR5ecto) complexed with a signalling competent fragment of mouse Rspo2 (mRspo2Fu1-Fu2). The structure shows that the particularly potent Rspo2 ligand engages LGR5 in a fashion almost identical to that reported for hRSPO1. Comparison of our hLGR5ecto structure with previously published structures highlights a surprising plasticity of the LGR ectodomains, characterised by a nearly 9 degrees or larger rotation of the N-terminal half of the horseshoe-like fold relative to the C-terminal half. We also report a low resolution hLGR5-mRspo2Fu1-Fu2-mZNRF3ecto ternary complex structure. This crystal structure confirms our previously suggested hypothesis, showing that Rspo proteins cross-link LGRs and ZNRF3 into a 2:2:2 complex, whereas a 1:1:1 complex is formed with RNF43.
Crystal structure of R-spondin 2 in complex with the ectodomains of its receptors LGR5 and ZNRF3.,Zebisch M, Yvonne Jones E J Struct Biol. 2015 Jun 26. pii: S1047-8477(15)00137-9. doi:, 10.1016/j.jsb.2015.05.008. PMID:26123262[4]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Hao HX, Xie Y, Zhang Y, Charlat O, Oster E, Avello M, Lei H, Mickanin C, Liu D, Ruffner H, Mao X, Ma Q, Zamponi R, Bouwmeester T, Finan PM, Kirschner MW, Porter JA, Serluca FC, Cong F. ZNRF3 promotes Wnt receptor turnover in an R-spondin-sensitive manner. Nature. 2012 Apr 29;485(7397):195-200. doi: 10.1038/nature11019. PMID:22575959 doi:10.1038/nature11019
- ↑ Koo BK, Spit M, Jordens I, Low TY, Stange DE, van de Wetering M, van Es JH, Mohammed S, Heck AJ, Maurice MM, Clevers H. Tumour suppressor RNF43 is a stem-cell E3 ligase that induces endocytosis of Wnt receptors. Nature. 2012 Aug 30;488(7413):665-9. doi: 10.1038/nature11308. PMID:22895187 doi:10.1038/nature11308
- ↑ Carmon KS, Gong X, Lin Q, Thomas A, Liu Q. R-spondins function as ligands of the orphan receptors LGR4 and LGR5 to regulate Wnt/beta-catenin signaling. Proc Natl Acad Sci U S A. 2011 Jul 12;108(28):11452-7. doi:, 10.1073/pnas.1106083108. Epub 2011 Jun 21. PMID:21693646 doi:https://dx.doi.org/10.1073/pnas.1106083108
- ↑ Zebisch M, Yvonne Jones E. Crystal structure of R-spondin 2 in complex with the ectodomains of its receptors LGR5 and ZNRF3. J Struct Biol. 2015 Jun 26. pii: S1047-8477(15)00137-9. doi:, 10.1016/j.jsb.2015.05.008. PMID:26123262 doi:https://dx.doi.org/10.1016/j.jsb.2015.05.008
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