Heparin Binds Lamprey Angiotensinogen and Promotes Thrombin Inhibition through a Template Mechanism.
J Biol Chem
; 291(48): 24900-24911, 2016 Nov 25.
Article
en En
| MEDLINE
| ID: mdl-27681598
Lamprey angiotensinogen (l-ANT) is a hormone carrier in the regulation of blood pressure, but it is also a heparin-dependent thrombin inhibitor in lamprey blood coagulation system. The detailed mechanisms on how angiotensin is carried by l-ANT and how heparin binds l-ANT and mediates thrombin inhibition are unclear. Here we have solved the crystal structure of cleaved l-ANT at 2.7 Å resolution and characterized its properties in heparin binding and protease inhibition. The structure reveals that l-ANT has a conserved serpin fold with a labile N-terminal angiotensin peptide and undergoes a typical stressed-to-relaxed conformational change when the reactive center loop is cleaved. Heparin binds l-ANT tightly with a dissociation constant of â¼10 nm involving â¼8 monosaccharides and â¼6 ionic interactions. The heparin binding site is located in an extensive positively charged surface area around helix D involving residues Lys-148, Lys-151, Arg-155, and Arg-380. Although l-ANT by itself is a poor thrombin inhibitor with a second order rate constant of 500 m-1 s-1, its interaction with thrombin is accelerated 90-fold by high molecular weight heparin following a bell-shaped dose-dependent curve. Short heparin chains of 6-20 monosaccharide units are insufficient to promote thrombin inhibition. Furthermore, an l-ANT mutant with the P1 Ile mutated to Arg inhibits thrombin nearly 1500-fold faster than the wild type, which is further accelerated by high molecular weight heparin. Taken together, these results suggest that heparin binds l-ANT at a conserved heparin binding site around helix D and promotes the interaction between l-ANT and thrombin through a template mechanism conserved in vertebrates.
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Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Angiotensinas
/
Heparina
/
Trombina
/
Proteínas de Peces
/
Lampreas
Límite:
Animals
Idioma:
En
Revista:
J Biol Chem
Año:
2016
Tipo del documento:
Article
Pais de publicación:
Estados Unidos