title: Direct evidence for specific interactions of the fibrinogen alphaC-domains with the central E region and with each other.
abstract: The carboxyl-terminal regions of the fibrinogen Aalpha chains (alphaC regions) form compact alphaC-domains tethered to the bulk of the molecule with flexible alphaC-connectors. It was hypothesized that in fibrinogen two alphaC-domains interact intramolecularly with each other and with the central E region preferentially through its N-termini of Bbeta chains and that removal of fibrinopeptides A and B upon fibrin assembly results in dissociation of the alphaC regions and their switch to intermolecular interactions. To test this hypothesis, we studied the interactions of the recombinant alphaC region (Aalpha221-610 fragment) and its subfragments, alphaC-connector (Aalpha221-391) and alphaC-domain (Aalpha392-610), between each other and with the recombinant (Bbeta1-66)2 and (beta15-66)2 fragments and NDSK corresponding to the fibrin(ogen) central E region, using laser tweezers-based force spectroscopy. The alphaC-domain, but not the alphaC-connector, bound to NDSK, which contains fibrinopeptides A and B, and less frequently to desA-NDSK and (Bbeta1-66)2 containing only fibrinopeptides B; it was poorly reactive with desAB-NDSK and (beta15-66)2 both lacking fibrinopeptide B. The interactions of the alphaC-domains with each other and with the alphaC-connector were also observed, although they were weaker and heterogeneous in strength. These results provide the first direct evidence for the interaction between the alphaC-domains and the central E region through fibrinopeptide B, in agreement with the hypothesis given above, and indicate that fibrinopeptide A is also involved. They also confirm the hypothesized homomeric interactions between the alphaC-domains and display their interaction with the alphaC-connectors, which may contribute to covalent cross-linking of alpha polymers in fibrin.
authors.affiliation: Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6058, USA. litvinov@mail.med.upenn.edu
authors.forename: Rustem I
authors.initials: RI
authors.lastname: Litvinov
authors.forename: Sergiy
authors.initials: S
authors.lastname: Yakovlev
authors.forename: Galina
authors.initials: G
authors.lastname: Tsurupa
authors.forename: Oleg V
authors.initials: OV
authors.lastname: Gorkun
authors.forename: Leonid
authors.initials: L
authors.lastname: Medved
authors.forename: John W
authors.initials: JW
authors.lastname: Weisel
mesh_terms: D001665:Binding Sites; D005337:Fibrin / Q000737:chemistry / Q000378:metabolism; D005340:Fibrinogen / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D005344:Fibrinopeptide A / Q000737:chemistry / Q000378:metabolism; D005345:Fibrinopeptide B / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D008954:Models, Biological; D052898:Optical Tweezers; D010446:Peptide Fragments / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry* / Q000378:metabolism
chemical_list: C115499:BBeta fibrinogen; D010446:Peptide Fragments; D021122:Protein Subunits; D011994:Recombinant Proteins; C098000:fibrinogen alphaC; C027539:fibrinopeptides gamma; D005344:Fibrinopeptide A; D005345:Fibrinopeptide B; D005337:Fibrin; D005340:Fibrinogen