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

Activated Factor XIII a2 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), α2-antiplasmin (1–15), and α2-antiplasmin (1–15 Q4N) all function as glutamine-containing substrates for activated Factor XIII a2. 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 α2-antiplasmin (1–15) are proposed to bind both at the catalytic site and at a neighboring apolar region.