Structural features associated with the binding of glutamine-containing peptides to Factor XIII

Activated Factor XIII a 2 catalyzes the formation of intermolecular γ-glutamyl-ε-lysyl cross-links in the fibrin network. Solution NMR studies were carried out to characterize, the structural features associated with the binding of glutamine-containing peptides to Factor XIII. A coupled uv/vis kinetic assay demonstrated that K9 peptide (1–10), α 2-antiplasmin (1–15), and α 2-antiplasmin (1–15 Q4N) all function as glutamine-containing substrates for activated Factor XIII a 2. 2D TOCSY spectra of the peptides exhibit upfield chemical shifts for the glutamine protons in the presence of Factor XIII. These results indicate that the reactive peptide glutamines are encountering a distinctive environment within the Factor XIII active site. 1D proton line-broadening and 2D transferred-NOESY studies reveal that the glutamines and residues located C-terminally come in direct contact with the enzyme and adopt an extended conformation. Substrates with sequences similar to α 2-antiplasmin (1–15) are proposed to bind both at the catalytic site and at a neighboring apolar region.