Members of this family adopt a fold similar to other EGF domains, with a flat major and a twisted minor beta sheet. Disulphide pairing, however, is not of the usual 1-3, 2-4, 5-6 type; rather 1-2, 3-4, 5-6 pairing is found. Its extended major sheet (strands beta-2 and beta-3 and the connecting loop) projects into thrombin's active site groove. This domain is required for interaction of thrombomodulin with thrombin, and subsequent activation of protein-C [1].

1: Structural basis for the anticoagulant activity of the thrombin-thrombomodulin complex. Fuentes-Prior P, Iwanaga Y, Huber R, Pagila R, Rumennik G, Seto M, Morser J, Light DR, Bode W; Nature. 2000;404:518-525. PMID:10761923