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Encyclopedia of Physical Science and Technology EN006P-81 June 29, 2001 21:48

848 Glycoconjugates and Carbohydrates

Sphingosine tain sialic acid are termed gangliosides (originally isolated
HO 3 CH CH CH (CH 3 ) 12 CH 3 from neural tissue) and are involved in development, es-
pecially in the nervous system.
X O
Fatty acid
CH N C
n
H V. ANALYTICAL METHODS
O X
CH 2
CH 2 OH
Classical methods for the determination of saccharide
X H O
H structures are rarely employed at this time. Thus, methyla-
Glucose OH H tion and periodate analyses, once the mainstay of carbohy-
Neutral glycolipids OH H
Glucosylcerebroside drate work, have been superseded by mass spectrometry
H OH
and nuclear magnetic resonance (NMR).
Considerthetypicalproblem—thatofdefiningthecom-
Di-, tri-, or Glc Gal pletestructureofanoligosaccharide(polysaccharide),free
Lactosylceramide tetrasaccharide
(a globoside) or combined. Unlike procedures for analysis of DNA or
proteins where automated methods provide rapid and un-
Neu5Ac ambiguous sequences, sugar sequences are not readily de-
termined. Needed are linkage positions, configurations,
Complex
oligosaccharide GalNAc and branching as well as identification of the specific sug-
Ganglioside GM2 Glc Gal
ars. In some cases, the use of specific enzymes can pro-
vide information about the linkage configuration but these
FIGURE 30 Ceramide and glycosphingolipid structures.
do not always work, rarely are quantitative, and often do
not discriminate between linkages. The advent of NMR
and are extremely diverse. They are found on cell surfaces has permitted complete analysis of oligosaccharides as
and function as receptors and immunologic determinants. long as sufficient material is available (or spectrometer
The blood group ABO system is defined by specific sugars time). Thus, the linkage configuration for pyranosides is
present on erythrocyte glycolipids; thus, type A is charac- readily apparent from the coupling constant between the
terized by alpha-linked N-acetylgalactosamine, type B by protons on carbons-1 and -2 of the sugar in question. The
alpha-linked galactose, etc. Glycosphingolipids that con- order of sugars and possible branching can be determined

TABLE I Representative Lectins and Their Ligands a
Lectin family and lectin Abbreviation Ligand(s)
Plant
Concanavalin A ConA Manα1—OCH 3
b
Griffonia simplicifolia lectin 4 GS4 Lewis b (Le ) tetrasaccharide
Wheat germ agglutinin WGA Neu5Ac(α2 → 3)Gal(β1 → 4)Glc
GlcNAc(β1 → 4)GlcNAc
Ricin Gal(β1 → 4)Glc
Animal
Galectin-1 Gal(β1 → 4)Glc
Mannose-binding protein A MBP-A High-mannose octasaccharide
Viral
Influenza virus hemagglutinin HA Neu5Ac(α2 → 6)Gal(β1 → 4)Glc
Polyoma virus protein 1 VP1 Neu5Ac(α2 → 3)Gal(β1 → 4)Glc
Bacterial
Enterotoxin LT Gal
Cholera toxin CT GM1 pentasaccharide
Source: Weiss, W. I., and Drickamer, K. (1996). Structural basis of lectin-carbohydrate
recognition. Annu. Rev. Biochem. 65, 441–473.
a More than 100 lectins are known. X-ray diffraction analyses of crystalline lectins suggest
a common protein architecture for the saccharide binding sites.