Yp. Fu et al., FORMATION OF THE HUMAN FIBRINOGEN SUBCLASS FIB(420) - DISULFIDE BONDSAND GLYCOSYLATION IN ITS UNIQUE (ALPHA(E) CHAIN) DOMAINS, Blood, 92(9), 1998, pp. 3302-3308
COS cell transfection has been used to monitor the assembly and secret
ion of fibrinogen molecules, both those of the subclass containing the
novel alpha(E) chain and those of the more abundant subclass whose al
pha chains lack alpha(E)'s globular C-terminus. That region, referred
to as the alpha(E)C domain, is closely related to the ends of beta and
gamma chains of fibrinogen (beta C and gamma C), Transfection of COS
cells with alpha(E), beta, and gamma cDNAs alone results in secretion
of the symmetrical molecule (alpha(E)beta gamma)(2), also known as Fib
(420) Cotransfection with cDNA for the shorter cr chain yielded secret
ion of both (alpha beta gamma)(2) and (alpha(E)beta gamma)(2) but no m
ixed molecules of the structure alpha alpha(E)(beta gamma)(2). Exploit
ing the COS cells' fidelity with regard to Fib(420) production, identi
fication was made of the highly conserved Asn667 as the sole site of N
-linked glycosylation in the cue chain. No evidence from Cys --> Ser r
eplacements was found for interchain disulfide bridges involving the f
our cysteines of the alpha(E)C domain, However, for fibrinogen secreti
on, the alpha(E), \beta, and gamma subunits do exhibit different requi
rements for integrity of the two intradomain disulfide bridges located
at homologous positions in their respective C-termini, indicating dis
similar structural roles in the process of fibrinogen assembly. (C) 1
998 by The American Society of Hematology.