The alpha(E)C domain of human fibrinogen-420 is a stable and early plasmin cleavage product.

Human fibrinogen-420, (alpha(E)betagamma)(2), was isolated from plasma and evaluated for its ability to form clots and for its susceptibility to proteolysis. Clotting parameters, including cross-linking of subunit chains, of this subclass and of the more abundant fibrinogen-340 (alphabetagamma)(2), were found to be similar, suggesting little impact of the unique alpha(E)C domains of fibrinogen-420 on coagulation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of plasmic digestion patterns revealed production from fibrinogen-420 of the conventional fibrinogen degradation products, X, Y, D, and E, to be comparable to that from fibrinogen-340 in all respects except the presence of at least 2 additional cleavage products that were shown by Western blot analysis to contain the alpha(E)C domain.

The EC domains of human fibrinogen420 contain calcium binding sites but lack polymerization pockets.

The extended (E) isoform unique to Fibrinogen420 (Fib420) is distinguished from the conventional chain of Fibrinogen340 by the presence of an additional 236-residue carboxyl terminus globular domain (EC). A recombinant form of EC (rEC), having a predicted mass of 27,653 Daltons, was expressed in yeast (Pichia pastoris) and purified by anion exchange column chromatography. Purified rEC appears to be predominantly intact, as judged by N-terminal sequence analysis, mass spectral analysis of the C-terminal cyanogen bromide (CNBr) fragment, and comparison of recognition by epitope-specific monoclonal antibodies.

Distribution of desmosomal proteins in F9 embryonal carcinoma cells and epithelial cell derivatives.

In diverse epithelia, cytoskeletal keratin intermediate filaments (IFs) associated with the cytoplasmic face of intercellular junctional desmosomes. The processes underlying desmosome formation and keratin IF interactions remain unclear. We have examined F9 embryonal carcinoma (EC) cell differentiation as a model for embryonic development of epithelial surface desmosomes.