title: The activation peptide of coagulation factor XIII is vital for its expression and stability.
abstract: 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 (8) FGGR(12) R 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.
authors.affiliation: Hemostasis Research Laboratory, University Clinic of Hematology, University Hospital of Bern, Bern, Switzerland.|Department of Clinical Research, University of Bern, Bern, Switzerland.
authors.forename: H
authors.initials: H
authors.lastname: Handrkova
authors.affiliation: Hemostasis Research Laboratory, University Clinic of Hematology, University Hospital of Bern, Bern, Switzerland.|Department of Clinical Research, University of Bern, Bern, Switzerland.
authors.forename: V
authors.initials: V
authors.lastname: Schroeder
authors.affiliation: Hemostasis Research Laboratory, University Clinic of Hematology, University Hospital of Bern, Bern, Switzerland.|Department of Clinical Research, University of Bern, Bern, Switzerland.|Department of Medicine, Spital Netz Bern Hospitals Tiefenau Ziegler, Bern, Switzerland.
authors.forename: H P
authors.initials: HP
authors.lastname: Kohler
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D003412:Cricetulus; D004789:Enzyme Activation; D004795:Enzyme Stability; D005176:Factor XIII / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D026122:Factor XIIIa / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D009154:Mutation; D010455:Peptides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011489:Protein Denaturation; D055503:Protein Multimerization; D013696:Temperature; D014162:Transfection; D011503:Transglutaminases / Q000378:metabolism
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; C061895:factor XIII activation peptide; D005176:Factor XIII; D026122:Factor XIIIa; D011503:Transglutaminases
keywords: dimerization; factor XIII; factor XIII activation peptide; plasma transglutaminase; protein stability