Chemistry Reference
In-Depth Information
species, a glycan containing bacillosamine (2,4 - diacetamido - 2,4,6 - trideoxyglucose)
modifi ed with further GalNAc residues (for abbreviations and structures of mono-
saccharides, see Chapter 1) is transferred to asparagine; the enzyme (PglB) required
to transfer this oligosaccharide displays homology to the catalytic subunit of the
eukaryotic oligosaccharyltransferase (STT3; see Figure 8.1) and can be expressed
in other bacterial species in order to synthesise novel glycoforms (i.e., new glyco-
sylated forms of proteins). Other examples of bacterial glycosylation include the
N
-glycan of the archaeal species
Methanococcus voltae,
which is a trisaccharide of
the form
1,3GlcNAc, and various
O
- glycans,
including addition of heptoses to specifi c proteins in wild-type strains of
Esche-
richia coli
, of FucNAc to the pilin of
Pseudomonas aeruginosa
(an opportunistic
β
ManNAcA6Thr
β
1,4GlcNAc3NAcA
β
Figure 8.1
Family tree of the STT3 oligosac-
charyltransferase catalytic subunit. Oligosac-
charyltransferase in eukaryotes, required for the
transfer of a dolichol-linked precursor to aspar-
agine residues, is a multi-subunit enzyme; one
of these subunits, called STT3 (there are indeed
two forms, 'A' and 'B', in many species), has
homologues also in those bacteria which also
N
-glycosylate some of their proteins. This com-
puter - derived ' family tree ' is based on aligning
the STT3 sequences of various prokaryotic and
eukaryotic species and features many of the
organisms mentioned in this chapter.
