title: Structural basis for angiopoietin-1-mediated signaling initiation.
abstract: Angiogenesis is a complex cellular process involving multiple regulatory growth factors and growth factor receptors. Among them, the ligands for the endothelial-specific tunica intima endothelial receptor tyrosine kinase 2 (Tie2) receptor kinase, angiopoietin-1 (Ang1) and Ang2, play essential roles in balancing vessel stability and regression during both developmental and tumor-induced angiogenesis. Despite possessing a high degree of sequence identity, Ang1 and Ang2 have distinct functional roles and cell-signaling characteristics. Here, we present the crystal structures of Ang1 both unbound and in complex with the Tie2 ectodomain. Comparison of the Ang1-containing structures with their Ang2-containing counterparts provide insight into the mechanism of receptor activation and reveal molecular surfaces important for interactions with Tie2 coreceptors and associated signaling proteins. Using structure-based mutagenesis, we identify a loop within the angiopoietin P domain, adjacent to the receptor-binding interface, which confers the specific agonist/antagonist properties of the molecule. We demonstrate using cell-based assays that an Ang2 chimera containing the Ang1 loop sequence behaves functionally similarly to Ang1 as a constitutive Tie2 agonist, able to efficiently dissociate the inhibitory Tie1/Tie2 complex and elicit Tie2 clustering and downstream signaling.
authors.affiliation: Structural Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
authors.forename: Xuehong
authors.initials: X
authors.lastname: Yu
authors.forename: Tom C M
authors.initials: TC
authors.lastname: Seegar
authors.forename: Annamarie C
authors.initials: AC
authors.lastname: Dalton
authors.forename: Dorothea
authors.initials: D
authors.lastname: Tzvetkova-Robev
authors.forename: Yehuda
authors.initials: Y
authors.lastname: Goldgur
authors.forename: Kanagalaghatta R
authors.initials: KR
authors.lastname: Rajashankar
authors.forename: Dimitar B
authors.initials: DB
authors.lastname: Nikolov
authors.forename: William A
authors.initials: WA
authors.lastname: Barton
mesh_terms: D042683:Angiopoietin-1 / Q000737:chemistry* / Q000378:metabolism*; D042702:Angiopoietin-2 / Q000737:chemistry / Q000378:metabolism; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D057809:HEK293 Cells; D006801:Humans; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D042810:Receptor, TIE-1 / Q000737:chemistry / Q000378:metabolism; D042787:Receptor, TIE-2 / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction; D055672:Static Electricity; D013329:Structure-Activity Relationship
chemical_list: D042683:Angiopoietin-1; D042702:Angiopoietin-2; D011994:Recombinant Proteins; D042810:Receptor, TIE-1; D042787:Receptor, TIE-2