Fig. 4.

N-linked glycoprotein glycosylation is altered in Cog7-deficient adult heads. (A) Total N-glycan abundance was increased in all three allelic combinations compared with wild type. (B) The major class of N-glycans in Drosophila includes those of the high mannose type and most of the high mannose glycans were increased in the Cog7 alleles. (C) The single most abundant N-glycan in the adult Drosophila head is the paucimannose glycan M3N2F, which was also increased in all Cog7 allelic combinations compared with the wild type. (D) Hybrid and complex type N-glycans were also increased, although not as consistently or as dramatically. (E) Neural-specific N-glycans, known as HRP-epitopes, were profoundly increased in the Cog7-deficient adult heads. (F) The least abundant complex glycans in Drosophila are sialylated with NeuAc; unlike the other classes of N-glycans, the only detected sialylated glycan was reduced in Cog7 mutants. (G) Full MS spectra zoomed to present the naturally occurring isotope distribution of the sialylated glycan quantified in (F) demonstrates reduced abundance of sialylated glycans in the Cog7 mutant. The three most abundant isotopes of the biantennary, disialylated complex glycan depicted in (F) correspond to the all ¹²C form (¹³C₀) and two other isotopic variants that contain either one or two heavy ¹³C atoms. All of the isotopic variants were reduced in the mutant backgrounds.