The activation peptide of coagulation factor XIII is vital for its expression and stability. (16th July 2015) - Handrkova, H.
Summary Background The human activation peptide of factor XIII (AP‐FXIII) comprises the first 37 amino acids of the N‐terminus and holds the FXIII in an inactive state. FXIII is activated either proteolytically by cleavage of AP‐FXIII by thrombin, or non‐proteolytically by high calcium concentrations. Objective To investigate the role of AP‐FXIII in the expression and stability of FXIII. Methods We cloned 13 FXIII variants with progressive truncations of AP‐FXIII from the N‐terminus (delN‐FXIII‐A), expressed them in mammalian cells, and measured their thermostability, activation, and transglutaminase activity. We also used in silico calculations to analyze the stability of hypothetical delN‐FXIII dimers and to identify crucial motifs within AP‐FXIII. Results Variants with deletions longer than the first 10 amino acids and an R11Q point mutant were not expressed as proteins. In silico calculations indicated that the sequence 8FGGR12R plays a substantial role in intersubunit interactions in FXIII‐A2 homodimers. In agreement with this prediction, the temperature stability of delN‐FXIII variants decreased with increasing length of deletion. These results may suggest a role of the N‐terminus of AP‐FXIII in dimer stability. Substantial sequence homology was found among activation peptides of vertebrate and even invertebrate (crustacean) FXIII‐A orthologs, which further supports our conclusion. Conclusions We conclude that deletion of 11 or more N‐terminal amino acids disrupts intersubunit interactions, which may prevent FXIII‐A2 homodimer formation. Therefore, AP‐FXIII plays an important role in the stability of the FXIII‐A2 dimer.