The structure of the B domain deleted fVIII heterodimer. (A,B) The fVIII domains are individually labeled and colored. The C-terminal end of the heavy chain and the N-terminal end of the light chain are indicated with residue numbers (715 and 1695). Residues 1563 to 1694 (the N-terminal 80 residues of the light chain) are present in the construct but are poorly ordered. The N- and C-termini of 2 additional disordered regions are also indicated with residue numbers: residues 220 and 228 that flank a surface loop in the A1 domain (right panel) and residues 334 and 366 that flank the linker region between the A1 and A2 domains (left panel). Shown are 2 bound calcium ions, 2 bound copper ions, and 3 well-ordered and visible N-linked oligosaccharide structures. Shown and labeled for reference are 4 residues on the C2 domain that are thought to be involved in membrane binding and a similarly positioned pair of residues on the C1 domain. (C) Anomalous difference peaks at the sites of bound copper ions buried in the A1 and A3 domains (contoured at 5σ; both are approximately 9σ peak height overall). The residues involved in metal binding at this site are conserved in the analogous copper-binding site in ceruloplasmin, but are diverged from fV. (D) Difference density for 1 of 3 N-linked oligosaccharide structures, which modifies Asn239 in the A1 domain. The density is readily apparent for the entire pentameric polysacharide mannose core of an N-linked sugar, and represents unbiased density prior to any modeling of the covalent modification.