TABLE 1.
Glycosylation of peptides identified in AIDA-Ia
| Peptide (designation) | No. of heptoses | Means of identification |
|---|---|---|
| Glycosylated peptides | ||
| K↓T95TATTVNSSGSQNVGTSGATISTIVNSGGIQR126↓ (P1) | 2, 3, or 4 | MS, ED |
| Y↓N147LGHASNTVIF157↓ (P2) | 0 or 1 | MS |
| R↓V240NSGAVATGTVLSGG- (P3) | NDb | ED |
| K↓G328SQIVNSEGTAINTLVSDGGYQHIR352↓ (P4a) | 0, 1, or 2 | MS, ED |
| L↓S323ANIKGSQIVNSEGTAINTLVSDGGY348↓ (P4b) | 2 | MS |
| R↓V389LSDGYAR396↓ (P5) | ND | ED |
| R↓E406NVSNGGVSYNAM- (P6) | ND | ED |
| Y↓I427YSDGEATAAIVNTSGF443↓ (P7) | 1 | MS |
| R↓Q536YVYSGATATSTVGNNEGR554↓ (P8a) | 0, 1, or 2 | MS, ED |
| Y↓V538YSGATATSTVGNNEGREY556↓ (P8b) | 1, 2 | MS |
| R↓E555YVLSGGITDGTVLNSGGLQAVSSGGK581↓ (P9) | 4 | MS, ED |
| K↓A582SATVINEGGAQFVYDGGQVTGTNIK607↓ (P10) | 0 or 1 | MS, ED |
| Unglycosylated peptides | ||
| Y↓Q349HIRNGGIASGTIVNQSGY367↓ | MS | |
| R↓G397TILNNSGR405↓ | ED | |
| K↓A470IDAEVYSGGK480↓ | ED | |
| Y↓S485GGEVSGTQIF495↓ | MS | |
| R↓L518NAFAGNVVGTILNQEGR535↓ | MS, ED | |
| K↓D739NTGIMTYAGTLTQAQGVNK759↓ | MS, ED | |
| K↓L824LLSATVNGSLVNNK837↓ | MS, ED | |
| K↓N838NIILNPTK845↓ | ED |
Glycosylated mature AIDA-I (corresponding to amino acids 50 to 847 in the preproprotein) was processed by digestion with trypsin or chymotrypsin, and the resulting peptides were identified by MS or ED. In MS, glycosylation of a peptide was identified as an excess of mass corresponding to a multiple of 192 Da (the mass of one heptose residue). In ED, glycosylated residues are identified when a signal corresponding to the modified residue is lacking or reduced during a degradation cycle. Two residues (S577, S578) showed an only 80% reduction in signal, suggesting that these residues were not modified in all peptides. The sequences of peptides P1, P3, and P6 could not be completely obtained by ED. Numbering corresponds to the positions of the amino acids in the preproprotein. MS yielded the number of heptose molecules bound per peptide. However, except in one case (T154), MS did not permit to identification of the modified residues. The number of heptoses cannot be determined using ED, but several residues (S102, S111, S116, S242, S252, S334, S391, S409, S540, S546, S559, S570, S577, S578, and S583) were identified as modified. Modified residues are underlined.
ND, not determined.