DOLICHOL IS NOT A NECESSARY MOIETY FOR LIPID-LINKED OLIGOSACCHARIDE SUBSTRATES OF THE MANNOSYLTRANSFERASES INVOLVED IN IN-VITRO N-LINKED-OLIGOSACCHARIDE ASSEMBLY
Ibh. Wilson et al., DOLICHOL IS NOT A NECESSARY MOIETY FOR LIPID-LINKED OLIGOSACCHARIDE SUBSTRATES OF THE MANNOSYLTRANSFERASES INVOLVED IN IN-VITRO N-LINKED-OLIGOSACCHARIDE ASSEMBLY, Biochemical journal, 310, 1995, pp. 909-916
Dolichol is utilized in vivo as an unusually large anchor on which the
precursor for N-linked oligosaccharides is assembled by a series of g
lycosyltransferases. The role of dolichol in enzyme substrate recognit
ion is investigated. Thus the biosynthetic intermediate NN'-diacetylch
itobiose was chemically linked to either dolichol or the much shorter
fully saturated tetraisoprenoid phytanol. Both lipids were used as sub
strates by a recombinant, soluble beta-1,4-mannosyltransferase. beta-[
H-3]Mannosylated lipids from this reaction were then used as substrate
s for the subsequent mannosyltransferases from yeast or rat liver micr
osomes. It was found that both the dolichyl- and phytanyl-linked subst
rates were easily mannosylated to form Man(5)GlcNAc(2), with some furt
her mannosylation to Man(7)GlcNAc(2) and Man9GlcNAc(2) at low concentr
ations of lipid-linked substrate. It is concluded that dolichol is not
necessary in vitro as part of the substrate for the mannosyltransfera
ses in the biosynthetic pathway for N-glycosylation.