Dolichol-dependent synthesis of chitobiosyl proteins and their further mannosylation. A second route for glycosylation of proteins in rat-spleen lymphocytes?

Unusual anionic N-linked oligosaccharides from bovine lung

We previously described a diverse family of sulfated anionic N-linked oligosaccharides released by peptide: N-glycosidase F (PNGaseF) from calf pulmonary artery endothelial (CPAE) cells (Roux, L., Holoyda, S., Sundblad, G., Freeze, H.H., and Varki, A. (1988) J. Biol. Chem. 263, 8879-8889). Since a major fraction of the intact lung consists of endothelial cells, we reasoned that bovine lung might be a rich source of similar molecules. Total N-linked oligosaccharides from bovine lung acetone powder were released by PNGaseF, labeled by [3H]NaBH4 reduction, and the anionic fractions were studied with a variety of techniques. The sugar chains with lesser negative charge (designated Class I) share several properties of conventional multiantennary complex-type chains. However, unlike the case with CPAE cells, sialic acids account only for a minority of the anionic properties and only a small proportion carry sulfate esters. A variety of different treatments indicate that most of the unexplained negative charge is due to multiple carboxylic acid groups. Resistance to beta-glucuronidase and alpha-iduronidase suggests that these may be previously undescribed modifications of mammalian oligosaccharides. The most highly charged N-linked chains (designated Class II) are more similar in general structure to the corresponding ones from CPAE cells, although relatively more abundant. Their high charge is primarily due to chondroitin sulfate, heparin/heparan sulfate, or keratan sulfate glycosaminoglycan chains. Sequential digestion studies suggest that a significant proportion of these molecules have more than one type of glycosaminoglycan chain associated with them. Compositional analysis indicates the presence of xylose residues in Class II, but not Class I molecules. However, unlike the case with conventional glycosaminoglycans, these residues are not at the reducing terminus. Most previously reported structures of complex-type N-linked oligosaccharides are derived from the glycoproteins of blood cells, plasma, or the secretions of cultured mammalian cells. This library of N-linked oligosaccharides from an intact mammalian organ (lung) contains a high proportion of novel anionic sugar chains whose structures are different from conventional complex-type sialylated chains and only partially related to those from CPAE cells. Further exploration of the N-linked chains of intact mammalian tissues seems warranted.

Microheterogeneity and structures of neutral glycans present in quail ovomucoid

Anionic chromatography of oligosaccharide-alditols obtained by alkaline hydrolysis of quail ovomucoid glycopeptides resulted in the isolation of a major neutral fraction (83%) which was separated into 14 fractions by high-performance liquid chromatography on an alkylamine silica column. The structures of nine oligosaccharide-alditols were determined. By the identification of mannobiosido-, and mannotriosido-di-N-acetylchitobiose mixed with N-acetyl-lactosaminic and oligomannosidic-types oligosaccharides, we demonstrate the high microheterogeneity of the glycans presents in the neutral fraction of this glycoprotein and suggest that ovomucoid glycosylation uses several pathways.

Biosynthesis of prolyl hydroxylase: evidence for two separate dolichol-media pathways of glycosylation

Prolyl hydroxylase is a glycoprotein containing two nonidentical subunits, alpha and beta. The alpha subunit of prolyl hydroxylase isolated from 13-day-old chick embryos contains a single high mannose oligosaccharide having seven mannosyl residues. Two forms of alpha subunit have been shown to exist in enzyme purified from tendon cells of 17-day-old chick embryos, one of which (alpha) appears to be identical in molecular weight and carbohydrate content with the single alpha of enzyme from 13-day-old chick embryos, as well as another form (alpha') that contains two oligosaccharides, each containing eight mannosyl units [see Kedersha, N. L., Tkacz, J. S., & Berg, R. A. (1985) Biochemistry (preceding paper in this issue)]. Biosynthetic labeling studies were performed with chick tendon cells using [2-3H]mannose, [6-3H]glucosamine, [14C(U)]mannose, and [14C(U)]glucose. Analysis of the labeled products using polyacrylamide gel electrophoresis in sodium dodecyl sulfate showed that only the oligosaccharides on alpha' incorporated measurable mannose or glucosamine isotopes; however, both alpha subunits incorporated 14C amino acid mix and [14C(U)]glucose [metabolically converted to [14C(U)]mannose] under similar conditions. Pulse-chase labeling studies using 14C amino acid mix demonstrated that both glycosylated polypeptide chains alpha and alpha' were synthesized simultaneously and that no precursor product relationship between alpha and alpha' was apparent. In the presence of tunicamycin, neither alpha nor alpha' was detected; a single polypeptide of greater mobility appeared instead. Incubation of the cells with inhibitory concentrations of glucosamine partially depressed the glycosylation of alpha' but allowed the glycosylation of alpha.(ABSTRACT TRUNCATED AT 250 WORDS)

The dolichol pathway of protein glycosylation in rat liver. Evidence that GTP promotes transformation of endogenous dolichyl phosphate into dolichylpyrophosphoryl-N-acetylglucosamine in stripped rough microsomes

Tunicamycin, an antibiotic which inhibits the transfer of N-acetylglucosamine 1-phosphate to dolichyl phosphate, has been used to decide whether or not, in stripped rough microsomes incubated with UDP-N-acetylglucosamine and GDP-mannose in the absence of detergent, the earliest effect of GTP in core glycosylation of proteins is to enhance synthesis of dolichylpyrophosphoryl-N-acetylglucosamine from endogenous dolichyl phosphate, or to transform this monoglycoside derivative into dolichylpyrophosphorylchitobiose. It has been found that the presence of tunicamycin in the reaction medium annihilates incorporation of N-acetylglucosamine and mannose into all kinds of glycoside derivative of dolichyl pyrophosphate, whereas dolichylphosphorylmannose is then formed in greater amount. Incorporation of N-acetylglucosamine into protein was also abolished; that of mannose was considerably reduced. Other experiments showed that transfer of N-acetylglucosamine 1-phosphate is the only reaction of the lipid intermediates pathway that becomes limiting after addition of tunicamycin in our GTP-stimulated system. Taking these and previous results from this laboratory [Godelaine et al. (1979) Eur. J. Biochem. 96, 17-26 and 27-34] into account, we conclude that GTP enhances the transformation of endogenous dolichyl phosphate into dolichylpyrophosphoryl-N-acetylglucosamine and leads to the complete assembly of dolichol-linked oligosaccharides which become ultimately transferred to protein. Triton X-100 increased the amount of dolichol glycosylated and markedly raised the ratio of labelled dolichylpyrophosphorylchitobiose to dolichylpyrophosphoryl-N-acetylglucosamine. Such changes being induced by GTP, we suggest that this nucleotide makes it possible to overcome a structural barrier of rough microsomes.

Effect of bis-(p-nitrophenyl) phosphate on the biosynthesis and the utilization of lipid-intermediates

Incubations of rat spleen lymphocytes with the required labelled nucleotide sugars lead to the formation of the various lipid-intermediates involved in the N-glycosylation of proteins. The effect of bis-(p-nitrophenyl) phosphate on the different reactions involved in the dolichol pathway has been studied. Although dolichyl phosphate mannose, dolichyl phosphate glucose and dolichyl diphosphate N-acetylglucosamine synthesis is not affected at all by bis-(p-nitrophenyl) phosphate (20 mM), this product inhibits completely the addition of the second N-acetylglucosamine residue on the dolichyl diphosphate N-acetylglucosamine acceptor. The addition of the five innermost mannose residues from GDP-mannose as donor is also strongly abolished. However, the addition of the more distal sugars, i.e. the four mannose residues using dolichyl phosphate mannose as donors and the additional glucose residues are only slightly affected. The reactions involved in the utilization of dolichyl diphosphate oligosaccharide, i.e. transfer to the proteins or degradation into soluble phospho-oligosaccharides, are also strongly inhibited. Thus bis-(p-nitrophenyl) phosphate appears to affect only the reactions involving the presence of dolichyl diphosphate sugar as substrate.