In our analysis of oligosaccharides from an insect cell viral protein w=
e
have come across what appears to be an unusual structure.
In an electrophorretic profile, relative to a glucose ladder standard, it
has a size of about 7 GU (glucose units). When we digest with jack bean
hexosaminidase it shifts downward 1.4 GU to 5.6 GU. Removal of 1 GlcNAc
usually results in a decrease of 0.75 GU in this system. So it appears
that 2 GlcNAc=92s were removed. However, at 5.6 GU this is still larger =
than
the trimannosyl core (4.0 ~ 4.2 GU) or fucosylated trimannosyl core (4.5 =
~
4.7 GU).
When this structure is further digested with jack bean mannosidase no
further digestion results. The structure remains at 5.6 GU. Fucosidase
digests remove 1 core fucose, but the structure is still larger by about
1.3 GU than the trimannosyl core. A combined digest with fucosidase and
hexosaminidase only gave the additive effect of the single digests--no
synergy suggesting outer arm fucose.
The structure is not digested by b-galactosidase or sialidase, nor does
longer exposure to hexosaminidase produce further digestion. At 5.6 GU
there is still a sugar molecule attached to this structure which prevents
complete digestion by combination of sialidase, b-galactosidase,
hexosaminidase, and a-mannosidase. We are using Oxford GlycoSystem's
sequencing enzymes.
We have also done monosaccharide analysis on the entire glycoform profile=
,
from which this oligosaccharide was purified, which only revealed the
presence of mannose, GlcNAc, and fucose; there was no indication of
galactose or sialic acid.
Anyone have any suggestions for possible structures?
Thanks
