The covalent structure of factor XIIIa crosslinked fibrinogen fibrils.
When factor XIIIa-mediated crosslinking of fibrin or fibrinogen occurs, reciprocal intermolecular isopeptide bonds form first between paired carboxy terminal gamma chain donor-acceptor sites in outer molecular D domains, resulting in gamma chain dimers. Their location in the fibrin polymer is not certain, but some evidence suggests they are situated at the outermost ends of the D domains of linearly aligned molecules comprising each strand of double-stranded fibrils ("DD-long"). Other experiments indicate that gamma chain bonds are located between D domains in opposing fibril strands ("transverse"). To distinguish between these possible arrangements, we evaluated the ultrastructure of fibrils and fibers found in factor XIIIa-fibrinogen crosslinking mixtures, based on this reasoning: if DD-long bonding occurs, single-stranded fibrils should result, whereas transverse positioning will result in double-stranded fibrils. Fibrils formed in partially cross-linked fibrinogen solutions consisted of two parallel strands, as discerned visually from scanning transmission electron microscopic images and confirmed by mass per unit length fibril measurements. Neighboring fibrinogen D domains in each fibril strand were aligned end-to-end and were in register with a fibrinogen E domain in the opposite strand, creating a half-staggered molecular arrangement with approximately 22.5-nm periodicity corresponding to half the length of fibrinogen. Ribbon-like fibrinogen fibers, like fibrils, displayed 22.5-nm periodicity, as expected from laterally associated double-stranded fibrils with D domains in register. Taken together, these results indicate that carboxy terminal gamma chain bonds are positioned transversely between strands and are represented by thin filamentous structures bridging the D domains of opposing fibril strands--it follows that the same gamma chain crosslink arrangement occurs in fibrin.
Mosesson
M W
MW
Sinai Samaritan Medical Center, University of Wisconsin Medical School, Milwaukee 53233, USA.
Siebenlist
K R
KR
Hainfeld
J F
JF
Wall
J S
JS
D002850:Chromatography, Gel; D003432:Cross-Linking Reagents; D004591:Electrophoresis, Polyacrylamide Gel; D005337:Fibrin / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*; D005340:Fibrinogen / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*; D018698:Glutamic Acid / Q000378:metabolism; D006629:Hirudins / Q000494:pharmacology; D006801:Humans; D008239:Lysine / Q000378:metabolism; D008854:Microscopy, Electron; D017348:Microscopy, Electron, Scanning Transmission; D008958:Models, Molecular; D008970:Molecular Weight; D011503:Transglutaminases / Q000378:metabolism*
D003432:Cross-Linking Reagents; D006629:Hirudins; D018698:Glutamic Acid; D005337:Fibrin; D005340:Fibrinogen; D011503:Transglutaminases; D008239:Lysine