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Galactosyltransferase 4 is a major control point for glycan branching in N-linked glycosylation.

McDonald AG, Hayes JM, Bezak T, Głuchowska SA, Cosgrave EF, Struwe WB, Stroop CJ, Kok H, van de Laar T, Rudd PM, Tipton KF, Davey GP - J. Cell. Sci. (2014)

Bottom Line: Galactosyltransferase, which acts on N-acetylglucosamine residues, was unexpectedly found to control metabolic flux through the glycosylation pathway and the level of final antennarity of nascent protein produced in the Golgi network.We identified a mechanism in which galactosyltransferase 4 isoform regulated N-glycan branching on the nascent protein, subsequently controlling biological activity in an in vivo model of hCG activity.We found that galactosyltransferase 4 is a major control point for glycan branching decisions taken in the Golgi of the cell, which might ultimately control the biological activity of nascent glycoprotein.

View Article: PubMed Central - PubMed

Affiliation: School of Biochemistry and Immunology, Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin 2, Ireland National Institute for Bioprocessing Research and Training (NIBRT), Fosters Avenue, Dublin 4, Ireland.

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GalT4 controls level of glycan antennarity and sialylation in N-linked glycosylation. (A) HILIC analysis of hCG immuno-purified from engineered cell lines shows that GalT4 knockdown causes substantial changes to the glycan profiles of the substrate glycoprotein (vii, viii, ix) suggesting that GalT4 is a major flux control point for glycan branching. (i) HCG, (ii) CHO-GnT4, (iii) CHO-GnT5, (iv) CHO-GnT4-GalT1, (v) CHO-GnT4-GalT2, (vi) CHO-GnT4-GalT3, (vii) CHO-GnT4-GalT4, (viii) CHO-GnT5-GalT4, (ix) CHO-GnT4,5-GalT4, (x) CHO-GnT4-GalT5, (xi) CHO-GnT4-GalT6. (B) GalT4 knockdown increases tri-sialylated glycan structures (S3) in CHO cells. WAX-HPLC of HCG from engineered cell lines and revealed a substantial increase in tri-sialylated structures in cell lines with GalT4 knockdown (v, vi, vii). (i) Bovine fetuin standard, (ii) HCG, (iii) CHO-GnT4, (iv) CHO-GnT5, (v) CHO-GnT4,5, (vi) CHO-GnT4-GalT4, (vii) CHO-GnT5-GalT4, (viii) CHO-GnT4,5-GalT4.
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f03: GalT4 controls level of glycan antennarity and sialylation in N-linked glycosylation. (A) HILIC analysis of hCG immuno-purified from engineered cell lines shows that GalT4 knockdown causes substantial changes to the glycan profiles of the substrate glycoprotein (vii, viii, ix) suggesting that GalT4 is a major flux control point for glycan branching. (i) HCG, (ii) CHO-GnT4, (iii) CHO-GnT5, (iv) CHO-GnT4-GalT1, (v) CHO-GnT4-GalT2, (vi) CHO-GnT4-GalT3, (vii) CHO-GnT4-GalT4, (viii) CHO-GnT5-GalT4, (ix) CHO-GnT4,5-GalT4, (x) CHO-GnT4-GalT5, (xi) CHO-GnT4-GalT6. (B) GalT4 knockdown increases tri-sialylated glycan structures (S3) in CHO cells. WAX-HPLC of HCG from engineered cell lines and revealed a substantial increase in tri-sialylated structures in cell lines with GalT4 knockdown (v, vi, vii). (i) Bovine fetuin standard, (ii) HCG, (iii) CHO-GnT4, (iv) CHO-GnT5, (v) CHO-GnT4,5, (vi) CHO-GnT4-GalT4, (vii) CHO-GnT5-GalT4, (viii) CHO-GnT4,5-GalT4.

Mentions: Initial HILIC profiles identified seven major 2-aminobenzamide (2-AB)-labelled N-glycan peaks from hCG (Fig. 3A). No significant changes were observed in the N-glycan profiles from cells overexpressing GnTIV or GnTV alone (Fig. 3Aii,iii) or GnTIV and GnTV together or from cells with only GalT knockdowns (data not shown). Overexpression of GnTIV or GnTV in combination with knockdown of galactosyltransferase (GalT4) caused significant changes to the N-glycan profiles of hCG from these cell lines, particularly in the region of higher GU values (9–11) (Fig. 3Avii,viii). These glycosylation changes were not present for other galactosyltransferase knockdowns (Fig. 3Aiv,v,vi,x,xi). Dual overexpression of GnTIV and GnTV together with GalT4 knockdown also resulted in substantial glycosylation changes to the substrate glycoprotein. Interestingly, a major increase was observed for a glycan structure at approximately GU 6.2 (see Fig. 3Aix).


Galactosyltransferase 4 is a major control point for glycan branching in N-linked glycosylation.

McDonald AG, Hayes JM, Bezak T, Głuchowska SA, Cosgrave EF, Struwe WB, Stroop CJ, Kok H, van de Laar T, Rudd PM, Tipton KF, Davey GP - J. Cell. Sci. (2014)

GalT4 controls level of glycan antennarity and sialylation in N-linked glycosylation. (A) HILIC analysis of hCG immuno-purified from engineered cell lines shows that GalT4 knockdown causes substantial changes to the glycan profiles of the substrate glycoprotein (vii, viii, ix) suggesting that GalT4 is a major flux control point for glycan branching. (i) HCG, (ii) CHO-GnT4, (iii) CHO-GnT5, (iv) CHO-GnT4-GalT1, (v) CHO-GnT4-GalT2, (vi) CHO-GnT4-GalT3, (vii) CHO-GnT4-GalT4, (viii) CHO-GnT5-GalT4, (ix) CHO-GnT4,5-GalT4, (x) CHO-GnT4-GalT5, (xi) CHO-GnT4-GalT6. (B) GalT4 knockdown increases tri-sialylated glycan structures (S3) in CHO cells. WAX-HPLC of HCG from engineered cell lines and revealed a substantial increase in tri-sialylated structures in cell lines with GalT4 knockdown (v, vi, vii). (i) Bovine fetuin standard, (ii) HCG, (iii) CHO-GnT4, (iv) CHO-GnT5, (v) CHO-GnT4,5, (vi) CHO-GnT4-GalT4, (vii) CHO-GnT5-GalT4, (viii) CHO-GnT4,5-GalT4.
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f03: GalT4 controls level of glycan antennarity and sialylation in N-linked glycosylation. (A) HILIC analysis of hCG immuno-purified from engineered cell lines shows that GalT4 knockdown causes substantial changes to the glycan profiles of the substrate glycoprotein (vii, viii, ix) suggesting that GalT4 is a major flux control point for glycan branching. (i) HCG, (ii) CHO-GnT4, (iii) CHO-GnT5, (iv) CHO-GnT4-GalT1, (v) CHO-GnT4-GalT2, (vi) CHO-GnT4-GalT3, (vii) CHO-GnT4-GalT4, (viii) CHO-GnT5-GalT4, (ix) CHO-GnT4,5-GalT4, (x) CHO-GnT4-GalT5, (xi) CHO-GnT4-GalT6. (B) GalT4 knockdown increases tri-sialylated glycan structures (S3) in CHO cells. WAX-HPLC of HCG from engineered cell lines and revealed a substantial increase in tri-sialylated structures in cell lines with GalT4 knockdown (v, vi, vii). (i) Bovine fetuin standard, (ii) HCG, (iii) CHO-GnT4, (iv) CHO-GnT5, (v) CHO-GnT4,5, (vi) CHO-GnT4-GalT4, (vii) CHO-GnT5-GalT4, (viii) CHO-GnT4,5-GalT4.
Mentions: Initial HILIC profiles identified seven major 2-aminobenzamide (2-AB)-labelled N-glycan peaks from hCG (Fig. 3A). No significant changes were observed in the N-glycan profiles from cells overexpressing GnTIV or GnTV alone (Fig. 3Aii,iii) or GnTIV and GnTV together or from cells with only GalT knockdowns (data not shown). Overexpression of GnTIV or GnTV in combination with knockdown of galactosyltransferase (GalT4) caused significant changes to the N-glycan profiles of hCG from these cell lines, particularly in the region of higher GU values (9–11) (Fig. 3Avii,viii). These glycosylation changes were not present for other galactosyltransferase knockdowns (Fig. 3Aiv,v,vi,x,xi). Dual overexpression of GnTIV and GnTV together with GalT4 knockdown also resulted in substantial glycosylation changes to the substrate glycoprotein. Interestingly, a major increase was observed for a glycan structure at approximately GU 6.2 (see Fig. 3Aix).

Bottom Line: Galactosyltransferase, which acts on N-acetylglucosamine residues, was unexpectedly found to control metabolic flux through the glycosylation pathway and the level of final antennarity of nascent protein produced in the Golgi network.We identified a mechanism in which galactosyltransferase 4 isoform regulated N-glycan branching on the nascent protein, subsequently controlling biological activity in an in vivo model of hCG activity.We found that galactosyltransferase 4 is a major control point for glycan branching decisions taken in the Golgi of the cell, which might ultimately control the biological activity of nascent glycoprotein.

View Article: PubMed Central - PubMed

Affiliation: School of Biochemistry and Immunology, Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin 2, Ireland National Institute for Bioprocessing Research and Training (NIBRT), Fosters Avenue, Dublin 4, Ireland.

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