Volume 271, Number 43,
Issue of October 25, 1996
pp. 26653-26658
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.
The Carbohydrate Moiety of the Bermuda Grass Antigen BG60
NEW OLIGOSACCHARIDES OF PLANT ORIGIN
(Received for publication, April 8, 1996, and in revised form, July 24, 1996)
Hiroyuki
Ohsuga
,
Song-Nan
Su
§
,
Noriko
Takahashi
,
Sue-Yee
Yang
§
,
Hiroaki
Nakagawa
,
Ichio
Shimada
¶
,
Yoji
Arata
¶
and
Yuan C.
Lee
From 
GlycoLab, Nakano Central Research Institute,
Nakano Vinegar Co., Ltd., Handa City, 475 Japan, the
§ Department of Medical Research, Veterans General Hospital,
Taipei, Taiwan 112, Republic of China, the ¶ Faculty of
Pharmaceutical Science, University of Tokyo, Hongo, Tokyo,113 Japan,
and the 
Department of Biology and McCollum-Pratt Institute, The
Johns Hopkins University, Baltimore, Maryland 21218
BG60 is an important allergen of
Bermuda grass (Cynodon dactylon) pollen, which causes
allergic responses in human. It was suggested that its carbohydrate
moiety may be relevant to allergic reaction (Su, S. N., Lau, G. X.,
Shu, P., Yang, S. Y., Huang, S. W., and Lee, Y. C. (1996) J. Allergy Clin. Immunol., in press). Therefore, the structure of
the carbohydrate moiety in BG60 was investigated. The
N-linked oligosaccharides were released from the
glycopeptides of BG60 by digesting with a glycoamidase from sweet
almond and reductively aminated with a fluorescent reagent,
2-aminopyridine. The mixture of pyridylaminated oligosaccharides were
separated by high-performance liquid chromatography (HPLC) using an
octadecylsilyl (ODS) column. Five oligosaccharide fractions were
isolated, and each fraction was found to be homogeneous by HPLC on an
amide-silica column. The structure of each of the oligosaccharides was
analyzed by the two-dimensional mapping technique (Tomiya, N., Awaya,
J., Kurono, M., Endo, S., Arata, Y., and Takahashi, N. (1988)
Anal. Biochem. 171, 73-90), in tandem with sequential
exoglycosidase digestion. The two most abundant oligosaccharides, A and
B, have an unusual structural feature, i.e. the presence of
an L-Fuc 
-(1,3)-linked to Asn-linked GlcNAc without a
Xyl 
-(1,2)-linked to the branching Man (see below). To the best of
our knowledge, these are the first such oligosaccharides found in plant
glycoproteins.
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Bermuda grass (Cynodon dactylon) pollen is one of the
most common causes for airway allergic disease in hot and humid climate
(, , ). It contains at least 53 antigenic proteins that can induce
immune response in rabbit (), of which more than 12 have been shown to
possess IgE binding activity (, , , ). One of the major allergens with an
apparent molecular weight of 56-60 kDa, designated BG60, was shown to
be a basic protein containing three to four components with the pI
values of 9.8-10.5. Two of the components, which share immunological
identities, have been purified and partially characterized (, ).
Recently, we reported that BG60 conatins 4.6% carbohydrate consisting
of mannose (Man), N-acetylglucosamine (GlcNAc), fucose (Fuc)
in an approximate ratio of 3:2:1 and a minute amount of xylose
().
The role of carbohydrate in allergens has been controversial. The best
known allergens, AgE and AgK of ragweed pollen, contain no carbohydrate
(, ). However, the involvement of the carbohydrate in antigenicity
has been repeatedly demonstrated (, , , ). Our recent study showed that
BG60 lost its ability to bind monoclonal antibody upon treatment with
periodate (). We now report the results of our structural
investigation on the carbohydrate moiety of BG60 and found its major
constituents are oligosaccharides hitherto unreported in the plant
glycoproteins.
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