4bk5 | pdb_00004bk5
crystal structure of the human EphA4 ectodomain in complex with human ephrin A5 (amine-methylated sample)
Structural highlights
Function[EPHA4_HUMAN] Receptor tyrosine kinase which binds membrane-bound ephrin family ligands residing on adjacent cells, leading to contact-dependent bidirectional signaling into neighboring cells. The signaling pathway downstream of the receptor is referred to as forward signaling while the signaling pathway downstream of the ephrin ligand is referred to as reverse signaling. Highly promiscuous, it has the unique property among Eph receptors to bind and to be physiologically activated by both GPI-anchored ephrin-A and transmembrane ephrin-B ligands including EFNA1 and EFNB3. Upon activation by ephrin ligands, modulates cell morphology and integrin-dependent cell adhesion through regulation of the Rac, Rap and Rho GTPases activity. Plays an important role in the development of the nervous system controlling different steps of axonal guidance including the establishment of the corticospinal projections. May also control the segregation of motor and sensory axons during neuromuscular circuit development. Beside its role in axonal guidance plays a role in synaptic plasticity. Activated by EFNA1 phosphorylates CDK5 at 'Tyr-15' which in turn phosphorylates NGEF regulating RHOA and dendritic spine morphogenesis. In the nervous system, plays also a role in repair after injury preventing axonal regeneration and in angiogenesis playing a role in central nervous system vascular formation. Additionally, its promiscuity makes it available to participate in a variety of cell-cell signaling regulating for instance the development of the thymic epithelium.[1] [EFNA5_HUMAN] Cell surface GPI-bound ligand for Eph receptors, a family of receptor tyrosine kinases which are crucial for migration, repulsion and adhesion during neuronal, vascular and epithelial development. Binds promiscuously Eph receptors residing on adjacent cells, leading to contact-dependent bidirectional signaling into neighboring cells. The signaling pathway downstream of the receptor is referred to as forward signaling while the signaling pathway downstream of the ephrin ligand is referred to as reverse signaling. Induces compartmentalized signaling within a caveolae-like membrane microdomain when bound to the extracellular domain of its cognate receptor. This signaling event requires the activity of the Fyn tyrosine kinase. Activates the EPHA3 receptor to regulate cell-cell adhesion and cytoskeletal organization. With the receptor EPHA2 may regulate lens fiber cells shape and interactions and be important for lens transparency maintenance. May function actively to stimulate axon fasciculation. The interaction of EFNA5 with EPHA5 also mediates communication between pancreatic islet cells to regulate glucose-stimulated insulin secretion. Cognate/functional ligand for EPHA7, their interaction regulates brain development modulating cell-cell adhesion and repulsion.[2] [3] Publication Abstract from PubMedFunctional outcomes of ephrin binding to Eph receptors (Ephs) range from cell repulsion to adhesion. Here we used cell collapse and stripe assays, showing contrasting effects of human ephrinA5 binding to EphA2 and EphA4. Despite equivalent ligand binding affinities, EphA4 triggered greater cell collapse, whereas EphA2-expressing cells adhered better to ephrinA5-coated surfaces. Chimeric receptors showed that the ectodomain is a major determinant of cell response. We report crystal structures of EphA4 ectodomain alone and in complexes with ephrinB3 and ephrinA5. These revealed closed clusters with a dimeric or circular arrangement in the crystal lattice, contrasting with extended arrays previously observed for EphA2 ectodomain. Localization microscopy showed that ligand-stimulated EphA4 induces smaller clusters than does EphA2. Mutant Ephs link these characteristics to interactions observed in the crystal lattices, suggesting a mechanism by which distinctive ectodomain surfaces determine clustering, and thereby signaling, properties. Structurally encoded intraclass differences in EphA clusters drive distinct cell responses.,Seiradake E, Schaupp A, Del Toro Ruiz D, Kaufmann R, Mitakidis N, Harlos K, Aricescu AR, Klein R, Jones EY Nat Struct Mol Biol. 2013 Jun 30. doi: 10.1038/nsmb.2617. PMID:23812375[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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