title: A comprehensive mechanism of fibrin network formation involving early branching and delayed single- to double-strand transition from coupled time-resolved X-ray/light-scattering detection.
abstract: The formation of a fibrin network following fibrinogen enzymatic activation is the central event in blood coagulation and has important biomedical and biotechnological implications. A non-covalent polymerization reaction between macromolecular monomers, it consists basically of two complementary processes: elongation/branching generates an interconnected 3D scaffold of relatively thin fibrils, and cooperative lateral aggregation thickens them more than 10-fold. We have studied the early stages up to the gel point by fast fibrinogen:enzyme mixing experiments using simultaneous small-angle X-ray scattering and wide-angle, multi-angle light scattering detection. The coupled evolutions of the average molecular weight, size, and cross section of the solutes during the fibrils growth phase were thus recovered. They reveal that extended structures, thinner than those predicted by the classic half-staggered, double-stranded mechanism, must quickly form. Following extensive modeling, an initial phase is proposed in which single-bonded "Y-ladder" polymers rapidly elongate before undergoing a delayed transition to the double-stranded fibrils. Consistent with the data, this alternative mechanism can intrinsically generate frequent, random branching points in each growing fibril. The model predicts that, as a consequence, some branches in these expanding "lumps" eventually interconnect, forming the pervasive 3D network. While still growing, other branches will then undergo a Ca(2+)/length-dependent cooperative collapse on the resulting network scaffolding filaments, explaining their sudden thickening, low final density, and basic mechanical properties.
authors.affiliation: Biopolimeri e Proteomica, IRCCS AOU San Martino-IST , I-16132 Genova, Italy.
authors.forename: Mattia
authors.initials: M
authors.lastname: Rocco
authors.forename: Matteo
authors.initials: M
authors.lastname: Molteni
authors.forename: Marco
authors.initials: M
authors.lastname: Ponassi
authors.forename: Guido
authors.initials: G
authors.lastname: Giachi
authors.forename: Marco
authors.initials: M
authors.lastname: Frediani
authors.forename: Alexandros
authors.initials: A
authors.lastname: Koutsioubas
authors.forename: Aldo
authors.initials: A
authors.lastname: Profumo
authors.forename: Didier
authors.initials: D
authors.lastname: Trevarin
authors.forename: Barbara
authors.initials: B
authors.lastname: Cardinali
authors.forename: Patrice
authors.initials: P
authors.lastname: Vachette
authors.forename: Fabio
authors.initials: F
authors.lastname: Ferri
authors.forename: Javier
authors.initials: J
authors.lastname: Pérez
mesh_terms: D005337:Fibrin / Q000138:chemical synthesis / Q000737:chemistry*; D007700:Kinetics; D008027:Light; D008958:Models, Molecular; D058105:Polymerization; D053838:Scattering, Small Angle; D013997:Time Factors; D014961:X-Ray Diffraction
chemical_list: D005337:Fibrin