In molecular biology, ornatin is a potent glycoprotein IIb-IIIa (GP IIb-IIIa) antagonist and platelet aggregation inhibitor isolated from Placobdella ornata (Turtle leech).
[1] The protein is 41-52 amino acids in length and contains the RGD recognition motif common in adhesion proteins, and 6 conserved cysteine residues.
These form three disulphide bonds, which are required for activity.
[2] The sequences of ornatin B, C, D and E are highly similar, while A2 and A3 are less similar, lacking the N-terminal 9 residues.
Ornatins share ~40% identity with decorsin, a GP IIb-IIIa antagonist isolated from the leech Macrobdella decora.