Alpha-Chain cross-linking in fibrin(ogen) Marburg
JH Sobel, I Trakht, HQ Wu, S Rudchenko and R Egbring
Department of Medicine, College of Physicians & Surgeons of Columbia
University, New York, NY 10032, USA.
The fibrinogen structural variant, Marburg (A alpha 1-460B beta gamma)2, is
comprised of normal B beta and gamma chains but contains severely truncated
A alpha chains that are missing approximately one half of their factor
XIIIa cross-linking domain. Immunochemical studies of fibrin(ogen) Marburg
were conducted to characterize the degree to which deletion of a defined A
alpha-chain segment, A alpha 461-610, can affect the process of fibrin
stabilization, ie, the factor XIIIa- mediated covalent interaction that
occurs between alpha chains of neighboring fibrin molecules and between
alpha chains and alpha 2 antiplasmin (alpha 2PI). The ability of Marburg
(and control) alpha chains to serve as a substrate for factor XIIIa and
undergo cross- linking was examined in an in vitro plasma clotting system.
The capacity for alpha-chain cross-linking was evaluated both as the
covalent incorporation of the small synthetic peptide, NQEQVSPLTLLK (which
represents the first 12 amino acids of alpha 2PI and includes the factor
XIIIa-sensitive glutamine residue responsible for the cross- linking of
alpha 2PI to fibrin), and as the appearance of native (ie, natural),
high-molecular-weight, cross-linked alpha-chain species. Antibodies
specific for the (A)alpha and gamma/gamma-gamma chains of fibrin(ogen) and
for the peptide and its parent protein, alpha 2PI (68 kD), were used as
immunoblotting probes to visualize the various cross- linked products
formed during in vitro clotting. Recalcification of Marburg plasma in the
presence of increasing concentrations of peptide resulted in the formation
of peptide-decorated Marburg alpha-chain monomers. Their size at the
highest peptide concentration examined indicated the incorporation of a
maximum of 3 to 4 mol of peptide per mole of alpha-chain. In the absence of
alpha 2PI 1-12 peptide, the alpha chains of Marburg fibrin cross-linked to
form oligomers and polymers, as well as heterodimers that included alpha
2PI. Both the peptide-decorated monomers and the native cross-linked
alpha-chain species of Marburg fibrin were smaller than their control
plasma counterparts, consistent with the truncated structure of the parent
Marburg A alpha chain. Collectively, the findings indicate that, although
deletion of the A alpha chain region no. 461-610 in fibrinogen Marburg
prevents formation of an extensive alpha polymer network (presumably due to
the absence of critical COOH-terminal lysine residues), it does not
interfere with initial events in the fibrin stabilization process, namely,
factor XIII binding and the ability of alpha chains to undergo limited
cross-linking to one another and to alpha 2PI.
Volume 86,
Issue 3,
pp. 989-1000,
08/01/1995
Copyright © 1995 by The American Society of Hematology
