Receptor tyrosine kinases of the Axl family are activated by the vitamin K-dependent protein Gas6. Axl signalling plays important roles in cancer, spermatogenesis, immunity, and platelet function. The crystal structure at 3.3 A resolution of a minimal human Gas6/Axl complex reveals an assembly of 2:2 stoichiometry, in which the two immunoglobulin-like domains of the Axl ectodomain are crosslinked by the first laminin G-like domain of Gas6, with no direct Axl/Axl or Gas6/Gas6 contacts ...
Receptor tyrosine kinases of the Axl family are activated by the vitamin K-dependent protein Gas6. Axl signalling plays important roles in cancer, spermatogenesis, immunity, and platelet function. The crystal structure at 3.3 A resolution of a minimal human Gas6/Axl complex reveals an assembly of 2:2 stoichiometry, in which the two immunoglobulin-like domains of the Axl ectodomain are crosslinked by the first laminin G-like domain of Gas6, with no direct Axl/Axl or Gas6/Gas6 contacts. There are two distinct Gas6/Axl contacts of very different size, both featuring interactions between edge beta-strands. Structure-based mutagenesis, protein binding assays and receptor activation experiments demonstrate that both the major and minor Gas6 binding sites are required for productive transmembrane signalling. Gas6-mediated Axl dimerisation is likely to occur in two steps, with a high-affinity 1:1 Gas6/Axl complex forming first. Only the minor Gas6 binding site is highly conserved in the other Axl family receptors, Sky/Tyro3 and Mer. Specificity at the major contact is suggested to result from the segregation of charged and apolar residues to opposite faces of the newly formed beta-sheet.
Related Citations:
Crystal Structure of a C-Terminal Fragment of Growth Arrest-Specific Protein Gas6 Sasaki, T., Knyazev, P.G., Cheburkin, Y., Goehring, W., Tisi, D., Ullrich, A., Timpl, R., Hohenester, E. (2002) J Biol Chem 277: 44164
Ligand Recognition and Homophilic Interactions in Tyro3 Heiring, C., Dahlback, B., Muller, Y.A. (2004) J Biol Chem 279: 6952
Organizational Affiliation:
Max-Planck-Institut für Biochemie, Martinsried, Germany.
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