Table I.

Quantitative analysis of processing rates measured in vitro with human immunoproteasomes and MUC1 (glyco)peptidesa

DesignationPeptide Sequence and Sites of O-GlycosylationProcessing Rate (%)
PeptidesP1 (HGV100)(GVTSAPDTRPAPGSTAPPAH)5100
P2 (AHG61)A(HGVTSAPESRPAPGSTAPPA)3100
P3 (AHG21-DTR)AHGVTSAPDTRPAPGSTAPPA100
P4 (AHG21-ESR)AHGVTSAPESRPAPGSTAPPA100
GalNAc-glycopeptidesGP1 (HGV100-G3-VTS,STA)(HGVTSAPDTRPAPGSTAPPA)5<1
GP2 (AHG21-G1-VTS)AHGVTSAPDTRPAPGSTAPPA57
GP3 (AHG21-G1-DTR)AHGVTSAPDTRPAPGSTAPPA94
GP4 (AHG21-G1-STA)AHGVTSAPDTRPAPGSTAPPA63
GP5 (AHG21-ES-G1-VTS)AHGVTSAPESRPAPGSTAPPA65
GP6 (AHG21-ES-G1-ESR)AHGVTSAPESRPAPGSTAPPA74
GP7 (AHG21-ES-G1-STA)AHGVTSAPESRPAPGSTAPPA64
GP8 (AHG21-G1-TSA)AHGVTSAPDTRPAPGSTAPPA70
GP9 (SAP20-G2-SAP,STA)SAPDTRPAPGSTAPPAHGVT54
GP10 (SAP20-G2-SAP,DTR)SAPDTRPAPGSTAPPAHGVT54
GP11 (SAP20-G3-SAPDTR,STA)SAPDTRPAPGSTAPPAHGVT65
GP12 (SAP20-G1-DTR)SAPDTRPAPGSTAPPAHGVT56
GP13 (SAP20-G2-DTR,STA)SAPDTRPAPGSTAPPAHGVT74
GP14 (SAP20-G1-STA)SAPDTRPAPGSTAPPAHGVT68
GP15 (HGV20-G2-VTS,STA)HGVTSAPDTRPAPGSTAPPA<1
GP16 (HGV20-G5)HGVTSAPDTRPAPGSTAPPA<1
Gal-GalNAc-glycopeptidesGGP1 (AHG21-GG1-VTS)AHGVTSAPDTRPAPGSTAPPA91
GGP2 (AHG21-GG1-DTR)AHGVTSAPDTRPAPGSTAPPA89
GGP3 (AHG21-GG1-STA)AHGVTSAPDTRPAPGSTAPPA88
GGP4 (AHG21-GG1-TSA)AHGVTSAPDTRPAPGSTAPPA86
NeuAc-Gal-GalNAc-glycopeptidesSGGP1 (AHG21-SGG1-VTS)AHGVTSAPDTRPAPGSTAPPA<1
SGGP2 (AHG21-SGG2-VTS)AHGVTSAPDTRPAPGSTAPPA<1
SGGP3 (AHG21-SGG2-STA)AHGVTSAPDTRPAPGSTAPPA<1
SGGP5 (AHG21-SGG5)AHGVTSAPDTRPAPGSTAPPA<1
  • a Synthetic peptides and glycopeptides were incubated with human immunoproteasomes and the digestion products were chromatographed by reverse-phase HPLC for quantification of the relative amounts of residual substrate. Peptides are named systematically starting with P followed by a running number, glycopeptides substituted with the monosaccharide GalNAc by the designation GP, those substituted with the disaccharide Gal-GalNAc or the trisaccharide NeuAc-Gal-GalNAc by GGP or SGGP, respectively. These designations are followed by a second systematic designation, which defines also the starting motif and length of the peptide, the number and type of glycans, and the sites of glycan substitution. The glycosylated amino acids are labeled with bold underlined letters.