Factor XIII is a transglutaminase which cross-links fibrin monomers.
The crystal structure has been determined for both the zymogen precursor and the activated Factor XIII. The N-terminal 37-peptide formed remains bound, and the conformation does not change significantly in the crystal structure. It is possible that the cleavage allows a conformational change which is necessary for substrate to access the active site. Here we see the backbones of the precursor and activated forms, with the active site highlighted in magenta and the cleavage site in green.