The fibrin Bβ125-135 site is involved in the lateral association of protofibrils

• Main Authors: E. Lugovskoi, N. Pydiura, Y. Makogonenko, L. Urvant, P. Gritsenko, I. Kolesnikova, N. Lugovska, S. Komisarenko
• Format: Article
• Language: English
• Published: National Academy of Sciences of Ukraine and Palladin Institute of Biochemistry of the National Academy of Sciences of Ukraine. 2020-06-01
• Series: Ukrainian Biochemical Journal
• Subjects: coiled-coil connector; fibrinogen to fibrin transition; hinge region; neoantigenic determinant; protofibril lateral association
• Online Access: http://ukrbiochemjournal.org/wp-content/uploads/2020/08/Lugovskoi_3_20.pdf
• ISSN: 2409-4943; 2413-5003

Earlier we reported that during the human fibrinogen to fibrin transition a neoantigenic determinant was exposed in the Bβ119-133 fragment, where a hinge locus is situated. The fibrin-specific mAb FnI-3c and its Fab-fragment with epitope in this fragment inhibited the lateral association of protofibrils. We suggested that the epitope coincided with a site involved in this process. In this work we investigated the epitope location more precisely and defined a functional role for its exposure in the hinge locus of the molecule. It was found that mAb FnI-3c bound to human, horse and rabbit fibrins, all of which have Lys in the position corresponding­ to human BβK130, but not to bovine and rat fibrins, which have other amino acid residues in this position, strongly suggesting that BβK130 provides the integral part of the epitope. This fact, homology data, and structural biological analysis of the amino acid sequences around BβK130 indicate that the site of interest is localized within Bβ125-135. The synthetic peptides Bβ121-138 and Bβ125-135, unlike their scrambled versions, bound to mAb FnI-3c in SPR analysis. Both peptides, but not their scrambled versions, inhibited the lateral association of protofibrils. The FnI-3c epitope is exposed after fibrinopeptide A cleavage and desA fibrin monomer formation. Structural biological analysis of the fibrinogen to fibrin transition showed a distinct increase of flexibility in the hinge locus. We propose that the structural transformation in the fibrin hinge regions leads to the conformation necessary for lateral association of protofibrils.