The N-linked oligosaccharides at the amino terminus of human apoB are important for the assembly and secretion of VLDL

We determined the role of N-linked glycosylation of apolipoprotein B (apoB) in the assembly and secretion of lipoproteins using transfected rat hepatoma McA-RH7777 cells expressing human apoB-17, apoB-37, and apoB-50, three apoB variants with different ability to recruit neutral lipids. Substituting Asn residue with Gln at the single glycosylation site within apoB-17 (N158) decreased its secretion efficiency to a level equivalent to that of wild-type apoB-17 treated with tunicamycin, but had little effect on its synthesis or intracellular distribution. When selective N-to-Q substitution was introduced at one or more of the five N-linked glycosylation sites within apoB-37 (N158, N956, N1341, N1350, and N1496), secretion efficiency of apoB-37 from transiently transfected cells was variably affected. When all five N-linked glycosylation sites were mutated within apoB-37, the secretion efficiency and association with lipoproteins were decreased by >50% as compared with wild-type apoB-37. Similarly, mutant apoB-50 with all of its N-linked glycosylation sites mutagenized showed decreased secretion efficiency and decreased lipoprotein association in both d < 1.02 and d > 1.02 g/ml fractions. The inability of mutant apoB-37 and apoB-50 to associate with very low-density lipoproteins was attributable to impaired assembly and was not due to the limitation of lipid availability. The decreased secretion of mutant apoB-17 and apoB-37 was not accompanied by accumulation within the cells, suggesting that the proportion of mutant apoB not secreted was rapidly degraded. However unlike apoB-17 or apoB-37, accumulation of mutant apoB-50 was observed within the endoplasmic reticulum and Golgi compartments.These data imply that the N-glycans at the amino terminus of apoB play an important role in the assembly and secretion of lipoproteins containing the carboxyl terminally truncated apoB. We determined the role of N-linked glycosylation of apolipoprotein B (apoB) in the assembly and secretion of lipoproteins using transfected rat hepatoma McA-RH7777 cells expressing human apoB-17, apoB-37, and apoB-50, three apoB variants with different ability to recruit neutral lipids. Substituting Asn residue with Gln at the single glycosylation site within apoB-17 (N158) decreased its secretion efficiency to a level equivalent to that of wild-type apoB-17 treated with tunicamycin, but had little effect on its synthesis or intracellular distribution. When selective N-to-Q substitution was introduced at one or more of the five N-linked glycosylation sites within apoB-37 (N158, N956, N1341, N1350, and N1496), secretion efficiency of apoB-37 from transiently transfected cells was variably affected. When all five N-linked glycosylation sites were mutated within apoB-37, the secretion efficiency and association with lipoproteins were decreased by >50% as compared with wild-type apoB-37. Similarly, mutant apoB-50 with all of its N-linked glycosylation sites mutagenized showed decreased secretion efficiency and decreased lipoprotein association in both d < 1.02 and d > 1.02 g/ml fractions. The inability of mutant apoB-37 and apoB-50 to associate with very low-density lipoproteins was attributable to impaired assembly and was not due to the limitation of lipid availability. The decreased secretion of mutant apoB-17 and apoB-37 was not accompanied by accumulation within the cells, suggesting that the proportion of mutant apoB not secreted was rapidly degraded. However unlike apoB-17 or apoB-37, accumulation of mutant apoB-50 was observed within the endoplasmic reticulum and Golgi compartments. These data imply that the N-glycans at the amino terminus of apoB play an important role in the assembly and secretion of lipoproteins containing the carboxyl terminally truncated apoB. The asparagine (N)-linked oligosaccharides of proteins are an important component of the quality control mechanisms of eucaryotic cells. Multiple roles have been assigned to N-linked oligosaccharides, including folding of nascent polypeptides, protection from proteolytic degradation, intracellular trafficking, secretion, cell surface expression, maintenance of protein conformation, and enzymatic activity (1Opdenakker G. Rudd P.M. Ponting C.P. Dwek R.A. Concepts and principles of glycobiology.FASEB J. 1993; 7: 1330-1337Google Scholar, 2Helenius A. How N-linked oligosaccharides affect glycoprotein folding in the endoplasmic reticulum.Mol. Biol. Cell. 1994; 5: 253-265Google Scholar, 3Imperiali B. Rickert K.W. Conformational implications of asparagine-linked glycosylation.Proc. Natl. Acad. Sci. USA. 1995; 92: 97-101Google Scholar). Human apolipoprotein (apo) B-100, a major structural protein of VLDL synthesized in the liver, is a 4,536 amino acid glycoprotein. There are 20 potential N-linked glycosylation sites within apoB-100, of which 16 Asn residues are conjugated with oligosaccharides on plasma LDL. Each mole of apoB-100 contains 5–6 mol of high-mannose type, and 8–10 mol of complex type oligosaccharides (4Taniguchi T. Ishikawa Y. Tsunemitsu M. Fukuzaki H. The structures of the asparagine-linked sugar chains of human apolipoprotein B-100.Arch. Biochem. Biophys. 1989; 273: 197-205Google Scholar). As a member of the vitellogenin family of lipid transport and storage proteins (5Baker M.E. Is vitellogenin an ancestor of apolipoprotein B-100 of human low-density lipoprotein and human lipoprotein lipase?.Biochem. J. 1988; 255: 1057-1060Google Scholar, 6Anderson T.A. Levitt D.G. Banaszak L.J. The structural basis of lipid interactions in lipovitellin, a soluble lipoprotein.Structure. 1998; 6: 895-909Google Scholar, 7Mann C.J. Anderson T.A. Read J. Chester S.A. Harrison G.B. Kochl S. Ritchie P.J. Bradbury P. Hussain F.S. Amey J. Vanloo B. Rosseneu M. Infante R. Hancock J.M. Levitt D.G. Banaszak L.J. Scott J. Shoulders C.C. The structure of vitellogenin provides a molecular model for the assembly and secretion of atherogenic lipoproteins.J. Mol. Biol. 1999; 285: 391-408Google Scholar), apoB-100 possesses numerous amphipathic α-helices and β-strands that constitute the major structural framework for the assembly and integrity of triglyceride-rich lipoproteins (8Chan L. Apolipoprotein B, the major protein component of triglyceride-rich and low density lipoproteins.J. Biol. Chem. 1992; 267: 25621-25624Google Scholar, 9Yao Z. McLeod R.S. Synthesis and secretion of hepatic apolipoprotein B-containing lipoproteins.Biochim. Biophys. Acta. 1994; 1212: 152-166Google Scholar). The precise amino acid sequences within apoB-100 that are involved in lipid binding have not yet been identified. The regions enriched in amphipathic β-strands are thought to interact directly and irreversibly with the VLDL neutral lipid core, whereas the regions rich in amphipathic α-helices are less tightly associated with lipid (10Shelness G.S. Sellers J.A. Very-low-density lipoprotein assembly and secretion.Curr. Opin. Lipidol. 2001; 12: 151-157Google Scholar). The minimum length of apoB that is required for the assembly of a neutral lipid core is between 23–28% of the N-terminal portion of apoB-100 (11McLeod R.S. Zhao Y. Selby S.L. Westerlund J. Yao Z. Carboxyl-terminal truncation impairs lipid recruitment by apolipoprotein B100 but does not affect secretion of the truncated apolipoprotein B-containing lipoproteins.J. Biol. Chem. 1994; 269: 2852-2862Google Scholar, 12McLeod R.S. Wang Y. Wang S. Rusinol A. Links P. Yao Z. Apolipoprotein B sequence requirements for hepatic very low density lipoprotein assembly. Evidence that hydrophobic sequences within apolipoprotein B48 mediate lipid recruitment.J. Biol. Chem. Scholar, of truncated of human apolipoprotein B in rat hepatoma cells. Evidence that the length of apolipoprotein B a major effect on the density of the secreted lipoproteins.J. Biol. Chem. Scholar). of as G.S. of in the assembly and secretion of apolipoprotein lipoproteins.J. Scholar, J. J. Wang Y. McLeod R. Yao Z. of within the amino terminus of human apolipoprotein Biol. Chem. 1998; 273: and Y. J. of apolipoprotein B is required for intracellular and transport of and Biol. Cell. Scholar, G. S. of the in apolipoprotein 1988; Scholar, of in rat apolipoprotein B Biophys. 1989; Scholar), have been to play a role in the assembly and secretion of for a role of N-linked oligosaccharides in not been with rat or that of N-linked glycosylation of apoB with the had major on VLDL secretion of on the secretion of proteins by of rat and on very low density and Biol. Chem. Scholar, J. T. P. of by rat of on lipoprotein J. Scholar, P. and assembly of and with and of very low density lipoprotein in the Biol. Chem. Scholar). with human cells showed that secretion of apoB-100 was by of N-linked glycosylation in of intracellular in hepatoma cells, and of are to associate with apolipoprotein B-100 in 1998; Scholar), and the decreased apoB-100 secretion in cells was associated with apoB J. Conformational in apolipoprotein B intracellular assembly and of lipoprotein in Biol. Scholar). with transfected McA-RH7777 cells that truncated of human observed that impaired apoB secretion in all cell These on the effect of that the of the and of for the with different the the role of apoB N-linked glycosylation using within three truncated of human apoB-17, apoB-37, and apoB-50, that have different to a neutral lipid that the N-linked oligosaccharides are important for secretion of apoB and and were from of and and protein were from The and was from and that were human apoB were a of R. and Y. of The was a of J. of was a of M. G. of The was from The that of the human apoB was by the sequence between and sites in at the of The N-to-Q substitution was introduced at using the to the The and were to and by a of the apoB in that was from Zhao Y. Yao Z. of human lipoproteins in rat hepatoma McA-RH7777 cells transfected with of synthesis of Biol. 1995; Scholar). and that N-to-Q at or and were by of using as a a of the apoB to the of in was from and J. J. Wang Y. McLeod R. Yao Z. of within the amino terminus of human apolipoprotein Biol. Chem. 1998; 273: that had been with The was as a to to of all for are from the The were by in a and the apoB regions were by McA-RH7777 cells were in containing and of the cells with wild-type or mutant of apoB-17, apoB-37, or apoB-50 was using the Yao for human apolipoprotein B100 in a rat hepatoma cell Biol. Chem. Scholar). of the human apoB was by of the using and R. of human low density Scholar, R. J. regions of apolipoprotein B-100 its Biol. Scholar). were using transiently transfected McA-RH7777 cells or of with cells were were with and to to the synthesis and secretion of apoB and are in the different the the cell and apoB and were and by in the of as R.S. Wang Y. Wang S. Rusinol A. Links P. Yao Z. Apolipoprotein B sequence requirements for hepatic very low density lipoprotein assembly. Evidence that hydrophobic sequences within apolipoprotein B48 mediate lipid recruitment.J. Biol. Chem. Scholar). the of apoB-50, the were d < 1.02 and d > 1.02 g/ml by to were with for and for in containing and as Wang Y. C.J. Z. Yao Z. The assembly of very low density lipoproteins in rat hepatoma McA-RH7777 cells is by Biol. Chem. Scholar). the of the and were in a density as J. S. on the assembly of apolipoprotein and very low density lipoproteins in McA-RH7777 Biol. Chem. 1994; 269: Scholar). The apoB proteins in were an that both human and rat and to and apoB-50, the were > and density by Y. Yao Z. The activity of protein is for accumulation of within in McA-RH7777 cells. model for the assembly of very low density lipoproteins.J. Biol. Chem. 1999; Scholar). The of the was as Y. Yao Z. The activity of protein is for accumulation of within in McA-RH7777 cells. model for the assembly of very low density lipoproteins.J. Biol. Chem. 1999; Scholar). were using a as Y. Yao Z. The activity of protein is for accumulation of within in McA-RH7777 cells. model for the assembly of very low density lipoproteins.J. Biol. Chem. 1999; Scholar). The was and on T. J. a Biochem. by in an A. control in the of a glycoprotein between the and Golgi Biol. 1994; Scholar, A. R.A. S. of protein between endoplasmic reticulum and Natl. Acad. Sci. USA. 1999; Scholar). of were and an of was to and to and of lipid with was as Y. Yao Z. The activity of protein is for accumulation of within in McA-RH7777 cells. model for the assembly of very low density lipoproteins.J. Biol. Chem. 1999; Scholar). expressing or were on for with in for 20 and with for was with for and the cells were with for 20 was to the human apoB with as The endoplasmic reticulum and Golgi were with and with conjugated as all cells were three with and were at cells were the using The were using the Human apoB-100 20 potential N-linked glycosylation of which 16 are conjugated with oligosaccharides McA-RH7777 cells expressing human apoB-17, apoB-37, or apoB-50, decreased secretion efficiency of the by as compared with the The secretion of apoB-100 in cells was decreased by effect of on secretion of rat apoB-100 was observed in rat not These that the of N-linked oligosaccharides is associated with impaired secretion of apoB. the role of N-linked oligosaccharides on apoB secretion, N-to-Q substitution at the glycosylation sites within apoB-17, apoB-37, and apoB-50 that different of N-glycans When the single glycosylation site within apoB-17 was the secretion efficiency of the mutant apoB-17 was decreased by as compared with the wild-type apoB-17 The effect of substitution on apoB-17 secretion was equivalent to that of The level of of and was in the cell by in The of was between the of N-linked oligosaccharides in proteins been to associate with A. How N-linked oligosaccharides affect glycoprotein folding in the endoplasmic reticulum.Mol. Biol. Cell. 1994; 5: 253-265Google Scholar). an the mechanisms for the impaired secretion of mutant apoB-17, determined the effect of the of on intracellular of were and with and by using and were as and Golgi was observed in the in or Golgi between and at or not These that the impaired secretion of was not associated with intracellular accumulation but with mechanisms in the hepatic cells by which synthesized apoB at the apoB or apoB Z. McLeod R.S. of synthesized apolipoprotein Scholar). of apoB or apoB is by which by or in McA-RH7777 cells J. J. Wang Y. McLeod R. Yao Z. of within the amino terminus of human apolipoprotein Biol. Chem. 1998; 273: Scholar). the role of in degradation, and of the intracellular of by at the of in the intracellular of or was observed These imply that is by The the of N-linked oligosaccharides in the secretion of apoB-17 the ability to neutral of truncated of human apolipoprotein B in rat hepatoma cells. Evidence that the length of apolipoprotein B a major effect on the density of the secreted lipoproteins.J. Biol. Chem. and is as a model for lipoprotein the role of N-linked oligosaccharides in the secretion of apoB-37 as a model that contains lipid binding sequences apoB-100 a structure of three amphipathic with amphipathic by the 1994; and N-linked glycosylation sites N-to-Q substitution at a single glycosylation site N956, N1341, N1350, and to is a N-linked that is important for lipoprotein with apoB-37 in different of apoB-37 as by of of apoB-37 had effect on the synthesis of or apoB-100 data not The N-to-Q substitution at single glycosylation site had a different effect on apoB-37 secretion secretion of and was not different from secretion of and decreased by compared with These data that N-to-Q substitution at a single N-linked glycosylation site or on apoB-37 the N-to-Q substitution at glycosylation sites and and decreased apoB-37 secretion all five glycosylation sites were the secretion efficiency of was decreased to of a level equivalent to that of treated with The secretion efficiency of or apoB-100 data not was not cells transiently transfected with apoB-37 of selective or N-to-Q substitution on apoB-37 secretion of the wild-type and mutant that single or more N-to-Q substitution at residues N956, N1341, N1350, and transfected cells were with for in the of the of cells were and rat and rat were and to and associated with and was of and in mutant cells is as the of apoB-37 or in cells. were with for and for was in and The secreted and at were to and of and at the of from mutant cells is as of apoB-37 or secreted from cells. for apoB-37 are the of to three of was determined of apoB the are of and apoB-37 with the of amino at The for and are by The in the of amino at the of the are of and on with human in transfected McA-RH7777 cells R.S. Wang Y. Wang S. Rusinol A. Links P. Yao Z. Apolipoprotein B sequence requirements for hepatic very low density lipoprotein assembly. Evidence that hydrophobic sequences within apolipoprotein B48 mediate lipid recruitment.J. Biol. Chem. was as a control for of selective or N-to-Q substitution on apoB-37 secretion of the wild-type and mutant that single or more N-to-Q substitution at residues N956, N1341, N1350, and transfected cells were with for in the of the of cells were and rat and rat were and to and associated with and was of and in mutant cells is as the of apoB-37 or in cells. were with for and for was in and The secreted and at were to and of and at the of from mutant cells is as of apoB-37 or secreted from cells. for apoB-37 are the of to three of was determined of apoB the are of and apoB-37 with the of amino at The for and are by The in the of amino at the of the are of and on with human in transfected McA-RH7777 cells R.S. Wang Y. Wang S. Rusinol A. Links P. Yao Z. Apolipoprotein B sequence requirements for hepatic very low density lipoprotein assembly. Evidence that hydrophobic sequences within apolipoprotein B48 mediate lipid recruitment.J. Biol. Chem. was as a control for was that N-to-Q substitution at in of and by in and of the the of within the apoB-37 the was by proteolytic at the carboxyl terminus of the mutant apoB-37, with a of As with and but not with The mutant with and but its with was apoB by on the is that at residue apoB-37 to proteolytic at amino acid residue of apoB These an important role of glycosylation at residue for the of apoB-37. of N-linked in proteolytic been for proteins of one asparagine-linked from human in and association with the endoplasmic Biol. Chem. 1992; 267: Scholar). The effect of N-to-Q substitution at all five N-linked glycosylation sites within apoB-37 was determined using of the of was observed by in showed that the secretion efficiency of was decreased by more as compared with that of which was to the effect of on secretion was in the of intracellular as compared with suggesting that the apoB-17 was rapidly The effect of on intracellular of apoB-37 was determined by using showed that at was in the in the or Golgi between and not The decreased secretion of was observed in both VLDL and lipoprotein that of lipoproteins the of N-linked oligosaccharides in a of in the the of N-linked glycosylation in apoB-37 not its secretion as the but impairs its ability to associate with neutral in VLDL assembly. The with apoB-37 that glycosylation is required for of to the proteolytic of that apoB sequences from the carboxyl terminus of apoB-37 the data less that of apoB a role in VLDL the to apoB-50 that the of sites as apoB-37 but contains more lipid binding sequences apoB-100 a structure of three amphipathic with amphipathic by the 1994; Scholar). the of the apoB-50 in the were with that of apoB-50 showed that unlike to mutant apoB-37, at not in apoB-50 not that amino acid sequences between the carboxyl of apoB-37 and apoB-50 the of the proteins introduced by We using cell that level of or to the effect of of on apoB-50 secretion in that secretion efficiency of was decreased in both d < 1.02 and d > 1.02 g/ml as compared with that of The of was that of which unlike or the mutant apoB-50 was not rapidly the transfected cells, the secretion efficiency of was as determined by in of in in apoB-100 secretion synthesis of apoB-100 was not not The effect of on apoB-100 secretion was of of apoB-50 apoB-100 secretion J. J. Wang Y. McLeod R. Yao Z. of within the amino terminus of human apolipoprotein Biol. Chem. 1998; 273: Scholar). of density of the the secretion of in both VLDL and The in secretion of as VLDL was observed by to not the decreased secretion was a of impaired the density of lipoproteins within the As in at the of associated with was and that associated with VLDL was as compared with the secretion as VLDL was attributable to a in assembly of neutral The inability of to was not attributable to synthesis or of in the transfected cells, as the synthesis of and as and the of not in and cells were There was in the activity of protein in transfected cells not These that the N-linked oligosaccharides play an important role in the assembly of VLDL containing The effect of the of on intracellular of apoB-50 was determined by by the of at was in the and Golgi the of was to that of not using with cells expressing or showed in in the or Golgi not to the effect of the of on intracellular was more directly determined using apoB proteins The and proteins the amino of apoB at carboxyl at the carboxyl terminus of not affect its ability to or as lipoproteins in transiently transfected McA-RH7777 cells and cell of and using not in intracellular not These data that the of N-glycans is not associated with in the intracellular of apoB. have compared the role of N-linked oligosaccharides between three truncated apoB apoB-17, apoB-37, and apoB-50, that have lipid binding The ability of human apoB to associate with neutral with the of amphipathic β-strands of apoB-17 apoB-100 a structure of three amphipathic with amphipathic by the 1994; Scholar, M. H. of lipid is determined by sequences in the N-terminal of Scholar), and of apoB and its secretion Z. McLeod R.S. of synthesized apolipoprotein Scholar). The apoB-17 the of apoB-100 H. of apolipoprotein B-100 in low density lipoproteins.J. 2001; Scholar), which is and is secreted as of truncated of human apolipoprotein B in rat hepatoma cells. Evidence that the length of apolipoprotein B a major effect on the density of the secreted lipoproteins.J. Biol. Chem. Scholar). apoB-17 is to neutral to binding A. G.S. in apolipoprotein B are for its binding to Biol. Chem. 1998; 273: Scholar, McLeod R. Yao Z. Scott J. Shoulders C.C. T. of in apolipoprotein B100 that a for the Biol. Chem. 1999; and is for lipid recruitment by lipid binding sequences D.G. S.L. Wang L. A. Yao Z. P. The amino terminus of apolipoprotein B is but not for protein Biol. Chem. Scholar). The in of with 1993; and cell with truncated of human apoB R.S. Wang Y. Wang S. Rusinol A. Links P. Yao Z. Apolipoprotein B sequence requirements for hepatic very low density lipoprotein assembly. Evidence that hydrophobic sequences within apolipoprotein B48 mediate lipid recruitment.J. Biol. Chem. Scholar, Z. McLeod R.S. of synthesized apolipoprotein have that the ability to VLDL at the length between and of a enriched with amphipathic β-strands apoB-100 a structure of three amphipathic with amphipathic by the 1994; Scholar). data have that the of N-glycans by in decreased secretion efficiency of the apoB of suggesting that the lipid binding sequences of apoB-17 to the for N-linked the that the of N-glycans not impairs secretion of apoB as the containing apoB-37 or but the association of apoB-37 and apoB-50 with neutral in in to lipid binding sequences of the N-linked oligosaccharides conjugated to apoB play a role the and lipid assembly. The that of a single in apoB-17 in impaired secretion of mutant is which that the structure not G.S. of in the assembly and secretion of apolipoprotein lipoproteins.J. Scholar, J. J. Wang Y. McLeod R. Yao Z. of within the amino terminus of human apolipoprotein Biol. Chem. 1998; 273: but N-linked The residue in apoB is between apoB and and is to a in that is between the the basis of the structure of lipovitellin, is to β-strands within the structure of the in human apoB C.J. Anderson T.A. Read J. Chester S.A. Harrison G.B. Kochl S. Ritchie P.J. Bradbury P. Hussain F.S. Amey J. Vanloo B. Rosseneu M. Infante R. Hancock J.M. Levitt D.G. Banaszak L.J. Scott J. Shoulders C.C. The structure of vitellogenin provides a molecular model for the assembly and secretion of atherogenic lipoproteins.J. Mol. Biol. 1999; 285: 391-408Google Scholar). the data a role of in apoB-17, showed that of the had on the secretion of G.S. of within the of apolipoprotein B for hepatic lipoprotein assembly and Biol. Chem. or apoB-50 J. J. Wang Y. McLeod R. Yao Z. of within the amino terminus of human apolipoprotein Biol. Chem. 1998; 273: Scholar). a role of the in apoB-17 folding and yet to for structural on the is that is of to apoB-17, in the of apoB-37 N-linked the single substitution effect on the mutant N-to-Q substitution at single site within apoB-37 had effect on its secretion, for The of in apoB-37 not in decreased secretion not to the as in but of and and with that proteolytic have at the carboxyl terminus of the protein and of apoB sequences the low molecular of was observed at the of within the the in the the the for of is are to that is of to apoB proteolytic not to mutant as a of of N-glycans been for mutant human of one asparagine-linked from human in and association with the endoplasmic Biol. Chem. 1992; 267: Scholar). When N-to-Q substitution at a single site was with that at that secretion of apoB-37 was impaired as the of mutated sites five These data the that of N-linked oligosaccharides in the of folding of proteins A. How N-linked oligosaccharides affect glycoprotein folding in the endoplasmic reticulum.Mol. Biol. Cell. 1994; 5: 253-265Google Scholar). The in the effect of on the to the proteolytic between apoB-37 and apoB-50 is that to in the of apoB-50, by of lipid binding sequences of apoB-37. The of is that an between lipid binding sequences and N-linked oligosaccharides in folding and of apoB. the for the impaired secretion of VLDL with apoB-37 or apoB-50 is is that the of N-glycans different on the of showed that the impaired secretion of mutant as was not accompanied with intracellular accumulation and was a intracellular of nascent The of an accumulation of or is of intracellular of mutant The of and is by that been in of including in the of the does of apoB-100 in transfected cells that or was in the that degradation, in the effect of of on cell apoB-50 was different from that on apoB-17 or apoB-37. have observed of The of apoB-50 within the that lipid binding sequences between the carboxyl of apoB-37 and apoB-50 the protein less to degradation, sequences for the of N-glycans for lipid the of of the role of N-linked glycosylation of apoB more directly the of tunicamycin, to determined or not the have structural that affect apoB of The mechanisms for of mutant apoB-17 and apoB-37 and for the of mutant apoB-50 within the cells to been the of a for of proteins are in the soluble proteins are to the Golgi and to the for S. and mechanisms are required for the quality control of endoplasmic reticulum protein Biol. 2001; Scholar). the of a secreted lipid binding mechanisms have been Z. McLeod R.S. of synthesized apolipoprotein Scholar, M. Wang H. H. The to nascent apolipoprotein B. Evidence for Biol. Chem. 2001; Scholar). is of to apoB and to the of to the of N-glycans in apoB affect apoB and the a of molecular as binding protein binding protein and protein were in containing VLDL within the of P. J. M. T. S. The assembly and secretion of apolipoprotein very low density lipoproteins in McA-RH7777 Biol. Chem. Scholar). The effect of the of N-glycans in apoB on its with molecular within the The that including molecular and of apoB as and N-linked are involved in the complex VLDL assembly and secretion The R. Y. M. G. and J. for in and H. and J. for the and in We for at of was by of the and of from the of and of and the and a of apolipoprotein endoplasmic reticulum protein protein

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