Density map of the B domain of fV short. Our recombinant fV short variant is 1 residue shorter than that from the transcripts of patients with East Texas bleeding disorder or healthy individuals³² because it lacks residue D756 or N756 in the B domain generated by a new codon across the I755-L1459 junction. Overall, the B domain fits the electron density map with the backbone and bulky side chains well, but features a higher degree of disorder in the portion proximal to the I755-L1459 junction, especially around the ⁷²⁶TALALENGT⁷³⁴ segment (A). The I755-L1459 junction is well-defined (B) and sits 10 Å away from R1545 and 57 Å from R709 (not shown), with I755 coming in contact with V1544. The C-terminal segment ¹⁵³⁴RDPDNIAAWYLR¹⁵⁴⁵ is the best-defined portion of the B domain (E). The fit of the electron density map progressively improves in the portion distal to the I755-L1459 junction (BCDE) because of tighter interactions with the A2 and A3 domains (Table 2; Figures 4 and 6). The preAR, from the splice site to T1492, comprises the hydrophobic patch ¹⁴⁸¹PLVIVG^{1486 29} and is well-defined (B), and so are the ascending (C) and descending (D) segments of the AR, from D1493 to D1537. The ¹⁵⁰⁷EDDY¹⁵¹⁰ wedge (D) penetrates a crevice in the A2 domain and defines the turn where the B domain changes direction (Figures 2B and 4B).