Structure of BDD-FVIII and locations of cysteine mutations. (A) The domain structure of full-length FVIII and BDD-FVIII. (B) The structure of BDD-FVIII as reported (Protein Data Bank ID, 3CDZ)²¹  and the individual domains (A1, A2, A3, C1, and C2) are color coded. Positions for selected cysteine mutations and site-directed PEGylation (F129, L491, K1804, K1808, and Q2091) are highlighted. Positions in FVIII that interact with FIX, FX, LRP, HSPG are indicated.