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Structure of the Repulsive Guidance Molecule (RGM)–Neogenin Signaling Hub

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Science  05 Jul 2013:
Vol. 341, Issue 6141, pp. 77-80
DOI: 10.1126/science.1232322

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RGM Proteins

Members of the repulsive guidance molecule (RGM) family of proteins can be secreted or reside on the surface of cells where they bind to the cell surface receptor, neogenin. The RGM proteins are named for their role in axon guidance for developing neurons, but their function is also linked to a range of human diseases, including inflammation, multiple sclerosis, and cancer. Bell et al. (p. 77) solved the crystal structures of the external portions of the RGMB protein with portions of neogenin. The structures revealed interactions of dimers of RGMB with neogenin in which ligand binding induced conformational changes that may initiate intracellular signaling from the receptor. RGM proteins contain a site of autocatalytic cleavage that affects secretion of the proteins, and some disease-associated mutations in RGM proteins were clustered at this site.

Abstract

Repulsive guidance molecule family members (RGMs) control fundamental and diverse cellular processes, including motility and adhesion, immune cell regulation, and systemic iron metabolism. However, it is not known how RGMs initiate signaling through their common cell-surface receptor, neogenin (NEO1). Here, we present crystal structures of the NEO1 RGM-binding region and its complex with human RGMB (also called dragon). The RGMB structure reveals a previously unknown protein fold and a functionally important autocatalytic cleavage mechanism and provides a framework to explain numerous disease-linked mutations in RGMs. In the complex, two RGMB ectodomains conformationally stabilize the juxtamembrane regions of two NEO1 receptors in a pH-dependent manner. We demonstrate that all RGM-NEO1 complexes share this architecture, which therefore represents the core of multiple signaling pathways.

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