title: Angiopoietin-1 and -2 coiled coil domains mediate distinct homo-oligomerization patterns, but fibrinogen-like domains mediate ligand activity.
abstract: Activity of endothelial Tie2 receptor tyrosine kinase is modulated by two naturally occurring, secreted ligands, angiopoietin-1 and -2, which have opposing effects on its phosphorylation. Receptor tyrosine kinase activation requires receptor dimerization/multimerization, which, for many receptors, is mediated by homo-oligomeric ligands binding to and bridging receptor molecules. We show here that angiopoietin-1 and -2 form distinct arrays of disulfide-linked homo-oligomeric complexes. Their mobilities on nonreducing gels suggest that angiopoietin-2 exists predominantly as a homodimer but also forms higher order multimers. In contrast, angiopoietin-1 forms some homotrimers, but predominantly exists in higher order multimers. These two structurally related, 60% homologous ligands are predominantly composed of an amino-terminal coiled coil domain and a carboxyl-terminal fibrinogen-like domain. We show that their distinct oligomerization patterns are determined by their coiled coil domains and, furthermore, that their coiled coil domains, but not their fibrinogen-like domains, are sufficient to mediate formation of disulfide-linked homo-oligomers. In contrast, the differential effects of these ligands on endothelial Tie2 phosphorylation is mediated by their fibrinogen-like domains. We conclude from these studies that the coiled coil and fibrinogen-like domains of the angiopoietins have distinct functions with the coiled coil domain mediating ligand homo-oligomerization and the fibrinogen-like domain mediating ligand activity.
authors.affiliation: Department of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6142, USA.
authors.forename: W N
authors.initials: WN
authors.lastname: Procopio
authors.forename: P I
authors.initials: PI
authors.lastname: Pelavin
authors.forename: W M
authors.initials: WM
authors.lastname: Lee
authors.forename: N M
authors.initials: NM
authors.lastname: Yeilding
mesh_terms: D042683:Angiopoietin-1; D042702:Angiopoietin-2; D000818:Animals; D001483:Base Sequence; D001704:Biopolymers; D002460:Cell Line; D017931:DNA Primers; D005340:Fibrinogen / Q000737:chemistry / Q000378:metabolism*; D008024:Ligands; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D010766:Phosphorylation; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D042787:Receptor, TIE-2
chemical_list: D042683:Angiopoietin-1; D042702:Angiopoietin-2; C467628:Angpt1 protein, mouse; D001704:Biopolymers; D017931:DNA Primers; D008024:Ligands; D008562:Membrane Glycoproteins; D011506:Proteins; D005340:Fibrinogen; D020794:Receptor Protein-Tyrosine Kinases; D042787:Receptor, TIE-2