Amino acid sequences surrounding R338 of FIX orthologs and FIXa structure. (A) R338 is indicated. Red-hued amino acids are evolutionary conserved, whereas positions highlighted by blue background are identical. (B) Ribbon rendering of partial structure of FIXa-WT (Protein Data Bank code: 1RFN) showing the protease domain in the standard orientation. R338 is highlighted in blue. The amino acids of the catalytic triad (H221, D269, S365) that form the enzymatic active site are shown in green.