There’s an enzyme in humans, called . It isn’t responsible for filling us with festive cheer, but is one of the enzymes responsible for blood clotting. It’s named after a child called Stephen Christmas who had a mutation in his Christmas Factor, otherwise known as coagulation Factor IX, causing haemophilia B (sometimes called Christmas Disease after him).
The role of Christmas Factor is to cleave a peptide bond in another enzyme, . In doing so, it activates this enzyme which is the next step of the clotting cascade that ultimately results in cross-linked fibrin and a blood clot.
The original Christmas mutation
Although there are more than 140 known mutations in the human Factor IX protein that give rise to haemophilia B, the original Christmas disease mutation, revealed by sequencing of Stephen Christmas� DNA, is a guanine to cytosine substitution. This changes cysteine 252 (shown in red in the image below) to serine, causing the loss of a disulphide bond right next to the active site of the enzyme (which is occupied by the purple P-amino benzamidine in the image below).
![Detail of Christmas Factor showing the mutation](/pdbe/sites/ebi.ac.uk.pdbe/files/images/structure_of_week/1rfn_xmasfactormutation.png" "Detail of Christmas Factor showing the mutation")
Haemophilia B patients with reduced levels of active Christmas Factor, rather than with no active enzyme, show only mild symptoms. This suggests that the enzyme could be partially inhibited without causing uncontrolled bleeding on injury, making it an attractive target for anti-coagulation drugs. Our in the PDBe search system allows you to see all the small molecules bound to Christmas Factor; many of them are potential therapeutics.
So if you slip with the knife while carving the turkey this Christmas, be very grateful that you have a fully functioning, stable Christmas Factor.
