Nuclear pore complex glycoproteins contain cytoplasmically disposed O-linked N-acetylglucosamine.

Abstract

Abstract. A novel form of protein-saccharide linkage consisting of single N-acetylglucosamine (GIcNAc) residues attached in O-linkages directly to the polypeptide backbone has been described (Holt, G. D., and G. W. Hart, 1986, J. Biol. Chem., 261:8049-8057). This modification was found on proteins distributed throughout the cell, although proteins bearing O-linked GIcNAc moieties were particularly abundant in the cytosolic and nuclear envelope fractions of rat liver. In the accompanying article (Snow, C. M., A. Senior, and L. Gerace, 1987, J. Cell. Biol., 104: 1143-1156, the authors describe monoclonal antibodies directed against eight proteins localized to the nuclear pore complex. These proteins occur on the cytoplasmic and nucleoplasmic (but not lumenal) sides of nuclear membranes. In this report, we demonstrate that all members of this group of pore complex proteins bear multiple O-linked GIcNAc residues. Further, we show that the O-linked GIcNAc moieties are linked via serine (and possibly threonine) side chains to these proteins. Perturbing the O-linked GIcNAc residues either by covalently attaching galactose to them or by releasing them with 13-N-acetylglucosaminidase strongly diminishes the immunoreactivity of the proteins with all of the monoclonal antibodies. However, the O-linked GIcNAc moieties are only part of the epitopes recognized, since O-GlcNAc-containing limit pronase fragments of nuclear pore complex proteins cannot be immunoprecipitated by these antibodies. These findings, taken together with those in the accompanying article, are a direct demonstration that proteins of the cytoplasm and nucleoplasm bear O-linked GIcNAc residues. p REVAILING evidence suggests that the bulk of the wellstudied types of carbohydrate moieties on glycoconjugates are either localized to the cell surface or within lumenal compartments of intracellular organelles (e.g., lysosomes, Golgi, and endoplasmic reticulum). In contrast, relatively little evidence has been obtained suggesting the existence of glycoproteins in the cytoplasmic and nucleoplasmic compartments of cells. Early studies involving carbohydrate analyses of nuclei and nuclear matrix fractions indicated the presence of glycoconjugates in these fractions (reviewed in Furukawa and Terayanm, 1979;Stein et al., 1981;Stoddart, 1979), and the presence of cytoplasmic glycoproteins has also been suggested (Meyer and Burger, 1976). These data have received support in several more recent investigations (e.g., Kan and Pinto da Silva, 1986;Fedarko and Conrad, 1986;Nagakura et al., 1986). However, attempts to identify and characterize nucleoplasmic and cytoplasmic glycoproteins have been severely hampered by cross-contamination with other cellular compartments, and detailed biochemical analyses of most putative cytoplasmic and nucleoplasmic glycoproteins is lacking.Recently the subcellular distribution of glycoproteins bearing terminal N-acetylglucosamine (GIcNAc) ~ residues was surveyed (Holt and Hart, 1986) by employing galactosyltransferase, an enzyme that trans...

Insights into O-Linked N-Acetylglucosamine ([0-9]O-GlcNAc) Processing and Dynamics through Kinetic Analysis of O-GlcNAc Transferase and O-GlcNAcase Activity on Protein Substrates

“…Recently, Rexach et al (52) developed a method to quantify the extent of O-GlcNAc modification of proteins using a resolvable polyethylene glycol mass tag. Their results demonstrated that Nup62 from adult rat brain is heavily O-GlcNAcylated, yielding a range of O-GlcNAc-modified species, an observation that is consistent with previous findings showing that Nup62 is heavily modified in cells (53). The results of the hOGT and hOGA kinetics also enable us to estimate the relative O-GlcNAc levels expected on different protein substrates at fixed concentrations of UDP-GlcNAc and both of the enzymes, assuming that no other factors are operative.…”

Ring cycle for dilating and constricting the nuclear pore

“…Especially noteworthy is that each Nup62 molecule, between the fingertip and N-terminal FG repeats, displays a heavily glycosylated region, each of which contains 10 single GlcNAc residues, linked to a Ser (Thr) residue (17,18). The physiological significance of what we termed the "glyco-belt" region ( Fig.…”

Metabolic cross-talk allows labeling of O-linked β- N -acetylglucosamine-modified proteins via the N -acetylgalactosamine salvage pathway

“…Then, we purified the labeled azidoglycoproteins via sequential anti-FLAG and immobilized metal affinity chromatographic steps and identified the captured proteins by two-dimensional liquid chromatography and tandem mass spectrometry. Importantly, numerous reported O-GlcNAcylated proteins were specifically enriched in the Ac 4 GalNAz-treated cells and absent from samples from vehicle-treated cells, including several components of the nuclear pore complex (known to be heavily glycosylated) (27,28), a Sec24 family member (29), glyceraldehyde-3-phosphate dehydrogenase (30), host cell factor C1 (31, 32), Elf-1 (33), and OGT itself (34,35) (Figs. S5B and S6).…”