1JMO, 1JMJ, 2NAT305315160ENSG00000099937ENSMUSG00000022766P05546P49182NM_000185NM_008223NM_001331047NP_000176NP_001317976NP_032249Heparin cofactor II (HCII), a protein encoded by the SERPIND1 gene, is a coagulation factor that inhibits IIa, and is a cofactor for heparin and dermatan sulfate ('minor antithrombin').1jmj: Crystal Structure of Native Heparin Cofactor II1jmo: Crystal Structure of the Heparin Cofactor II-S195A Thrombin Complex Heparin cofactor II (HCII), a protein encoded by the SERPIND1 gene, is a coagulation factor that inhibits IIa, and is a cofactor for heparin and dermatan sulfate ('minor antithrombin'). The product encoded by this gene is a serine proteinase inhibitor which rapidly inhibits thrombin in the presence of dermatan sulfate or heparin. The gene contains five exons and four introns. This protein shares homology with antithrombin and other members of the alpha 1-antitrypsin superfamily. Mutations in this gene are associated with heparin cofactor II deficiency.