TABLE 1.
Isobaric glycoforms of sVSG221 identified by ES-MS
The molecular weights of different glycoforms of sVSG221 were calculated according to the indicated compositions (in parentheses is the theoretical mass of the assigned VSG composition). The relative abundances of those glycoforms observed in Fig. 3 for sVSG preparations from WT cells and TbGT11 null mutant cells are indicated by: −, trace, +, ++, and +++ scores.
| Molecular mass WT/TbGT11 null mutant (theoretical) | Proteina | GlcN-Ino-cPb | EtNP | GlcNAc | Man + Gal | WT | TbGT11 null mutant |
|---|---|---|---|---|---|---|---|
| Da | |||||||
| 50364/50364 (50356) | 1 | 1 | 1 | 4 | 17 | +c | Traces |
| 50404/50404 (50397) | 1 | 1 | 1 | 5 | 16 | Traces | Traces |
| 50525/50526 (50518) | 1 | 1 | 1 | 4 | 18 | ++ | ++ |
| 50566/50567 (50559) | 1 | 1 | 1 | 5 | 17 | Traces | Traces |
| 50607/NA (50600) | 1 | 1 | 1 | 6 | 16 | Traces | − |
| 50687/50688 (50680) | 1 | 1 | 1 | 4 | 19 | +++ | +++ |
| 50730/50731 (50721) | 1 | 1 | 1 | 5 | 18 | + | Traces |
| 50850/50850 (50842)d | 1 | 1 | 1 | 4 | 20 | +++ | +++ |
| 50891/50894 (50883) | 1 | 1 | 1 | 5 | 19 | ++ | + |
| 50933/NA (50924) | 1 | 1 | 1 | 6 | 18 | Traces | − |
| 51012/51012 (51004) | 1 | 1 | 1 | 4 | 21 | ++ | +++ |
| 51053/51053 (51045) | 1 | 1 | 1 | 5 | 20 | +++ | ++ |
| 51096/51103 (51086) | 1 | 1 | 1 | 6 | 19 | + | Traces |
| 51174/51174 (51166) | 1 | 1 | 1 | 4 | 22 | + | + |
| 51215/51215 (51207) | 1 | 1 | 1 | 5 | 21 | +++ | ++ |
| 51257/51261 (51248) | 1 | 1 | 1 | 6 | 20 | + | Traces |
| 51337/51337 (51328) | 1 | 1 | 1 | 4 | 23 | + | + |
| 51377/51377 (51369) | 1 | 1 | 1 | 5 | 22 | + | + |
| 51419/51420 (51410) | 1 | 1 | 1 | 6 | 21 | + | Traces |
| 51499/51499 (51490) | 1 | 1 | 1 | 4 | 24 | + | + |
| 51540/51540 (51531) | 1 | 1 | 1 | 5 | 23 | + | + |
| 51580/NA (51572) | 1 | 1 | 1 | 6 | 22 | + | − |
| 51662/51661 (51652) | 1 | 1 | 1 | 4 | 25 | + | + |
| 51703/51702 (51693) | 1 | 1 | 1 | 5 | 24 | + | Traces |
| 51743/NA (51734) | 1 | 1 | 1 | 6 | 23 | Traces | − |
a Protein Mr is based on the amino acid sequences of the VSG221 precursor (accession no. P26332) minus residues 1–27 (signal peptide) and 460–476 (GPI attachment signal peptide) and allows for four disulfide bonds (Mr = 46,284).
b Components specific to the GPI anchor and common to all glycoforms: GlcN-Ino-cP, glucosamine-α1–6-myo-inositol-1,2 cyclic phosphate; EtNP, ethanolamine phosphate.
c Maximum entropy deconvolved spectra are only semi-quantitative; an indication of the relative abundance of the isobaric glycoforms is given based on peak height.
d The most abundant glycoform of WT sVSG221 is expected to contain a GPI anchor of composition of Man3Gal5, a C-terminal N-linked glycan of Man9GlcNAc2, and an internal N-linked glycan of Man3GlcNAc2 (i.e. GlcNAc = 4, and Man = 20).