Glycopeptide analysis by matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry reveals novel features of horseradish peroxidase glycosylation.
We explored matrix-assisted laser desorption/ionization (MALDI) tandem time-of-flight (TOF/TOF) mass spectrometry for the analysis of N-glycosylated peptides, using horseradish peroxidase (HRP) as a test case. Two different types of cleavage were observed in the TOF/TOF fragmentation spectra: Firstly, cleavages of peptide bonds yielded fragments with the attached N-glycans staying intact, thus revealing information on peptide sequence and glycan attachment site. Secondly, fragmentation of the glycan moiety was characterized by cleavage of glycosidic bonds as well as a (0,2)X-ring fragmentation of the innermost N-acetylglucosamine of the chitobiose core. Loss of the complete N-glycan moiety occurred by cleavage of both the N-glycosidic bond and the side-chain amide group of the N-glycosylated asparagine, yielding a characteristic peak doublet with a mass difference of 17 Da, which revealed the individual masses of the N-glycan and the peptide moiety. Analysis of a HRP tryptic digest at the sub-picomole level allowed the characterization of various N-glycosylated peptides including those with internal disulfide linkages, a glycopeptide linked via a disulfide bond to another peptide, and a 5 kDa glycopeptide carrying two N-glycans. The potential of our approach was illustrated by the detection of the following novel features of HRP glycosylation: (i) The conjugation of a xylosylated trimannosyl N-glycan without core-fucosylation to site Asn316, showing for the first time unambiguously the occupation of this site; and (ii) A disaccharide N-acetylhexosamine1deoxyhexose1 attached to N-glycosylation sites Asn285 and Asn298, which might represent a Fuc(alpha1-3)GlcNAc- moiety arising from the processing of N-glycans by a horse-radish endoglycosidase during biosynthesis of HRP.
Biomolecular Mass Spectrometry Unit, Department of Parasitology, Leiden University Medical Center, P.O. Box 9600, 2300 RC Leiden, The Netherlands. m.wuhrer@lumc.nl
Manfred
M
Wuhrer
Cornelis H
CH
Hokke
André M
AM
Deelder
D000595:Amino Acid Sequence; D006020:Glycopeptides / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D006031:Glycosylation; D006735:Horseradish Peroxidase / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014357:Trypsin / Q000378:metabolism
D006020:Glycopeptides; D010446:Peptide Fragments; D006735:Horseradish Peroxidase; D014357:Trypsin