Carbohydrate Analysis
271
Tab. 4
(
continued
)
Lectin
Systematic name
Abbreviation
Useful speciFcity
a
Example (a–f
designate parts of
±ig. 2)
Potato
Solanum tuberosum
STA
GlcNAc(
β
1
4)
GlcNAc(
β
1
4)
GlcNAc(
β
1
4)
Gorse seed
Ulex europaeus
UEA-I
Terminal fucose(
α
1
)
(b), blood type H
(O)
d
Wheat germ
Triticum vulgaris
WGA
Internal
GlcNAc(
β
1
4)
Man(
β
1
4)
(f)
a
For abbreviations, see Fig. 1.
b
Fuc
α
1
,
2
GalNAc
1
3
)
Gal
1
3or4
)
GlcNAc
1
R
)
c
Fuc
α
1
,
2
Gal
1
3
)
Gal
1
3or4
)
GlcNAc
1
R
)
d
Fuc
α
1
,
2
Gal
1
3or4
)
GlcNAc
1
R
)
Conformational analysis requires indepen-
dent data for each independent torsion
angle (
φ
,
ψ
, and sometimes
ω
)a
n
d
,
where mixtures of conformations exist,
the relative population occupancy of each.
These may be available from interresidue
proton NOE (e.g. between the anomeric
proton and the proton on the linkage car-
bon, H–C
1
–O–C
n
–H) and the
3
J
COCH
,
3
J
COCC
,
3
J
CCCH
,and
2
J
COC
coupling con-
stants, but the cosine nature of the Karplus
equation for
3
J
coupling means modeling
may be required. Whilst the conformation
of rigid oligosaccharides can be directly
derived from NOESY data, the upper and
lower bounds of the possible distances
from NOESY often enclose a large num-
ber of
φ
and
ψ
combinations. As multiple
conformations are often in fast equilib-
rium on the NMR timescale and NMR
data is effectively time-averaged, unrealis-
tic putative torsional angles may arise and
must be discriminated using molecular
modeling (Sect. 2.3.6).
Although NMR is an extremely powerful
tool, it has not yet been proved possible
tousei
tonin
tac
tg
lycop
ro
te
insbecause
of the complexity of the multitude of
overlapping peaks in the spectra. A further
limitation of NMR is that it requires
samples of at least about 25 nmol (i.e.
milligram amounts).
2.5
Use of Lectins
Lectins
are
widespread
and
serve
in
many
biologically
signi±cant
activities,
such as agglutinating cells and precipi-
tating glycoproteins and polysaccharides.
Because of this, many lectins are ex-
tremely toxic. The carbohydrate binding
sites are large and able to distinguish
complex carbohydrate structures (Table 4).
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