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Prominent 85‐kDa Oligomannosidic Glycoproteins of Rat Brain Are Signal Regulatory Proteins and Include the SHP Substrate‐1 for Tyrosine Phosphatases
Author(s) -
Bartoszewicz Z. P.,
Jaffe H.,
Sasaki M.,
Möller J. R.,
Stebbins J. W.,
Gebrekristos H.,
Quarles R. H.
Publication year - 1999
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1999.721688.x
Subject(s) - biochemistry , glycoprotein , sialic acid , fucose , chemistry , mannose , tyrosine , affinity chromatography , protein tyrosine phosphatase , amino acid , biology , enzyme
The glycoprotein component in rat brain reacting most strongly with Galanthus nivalis agglutinin (GNA) on western blots migrates as an 85‐kDa band. GNA identifies mannose‐rich oligosaccharides because it is highly specific for terminal α‐mannose residues. After purification of this 85‐kDa glycoprotein band by chromatography on GNA‐agarose and preparative gel electrophoresis, binding of other lectins demonstrated the presence of fucose and a trace of galactose, but no sialic acid. Treatment with N ‐Glycanase or endoglycosidase H produced a 65‐kDa band, indicating that it consisted of about one‐fourth N‐linked oligomannosidic carbohydrate moieties. High‐performance anion‐exchange chromatography and fluorescence‐assisted carbohydrate electrophoresis indicated that the major carbohydrate moiety is a heptasaccharide with the structure Manα1‐6(Manα1‐3)Manα1‐6(Manα1‐3)Manβ1‐4Glc‐NAcβ1‐4GlcNAc (Man 5 GlcNAc 2 ). Determination of amino acid sequences of peptides produced by endoproteinase digestion demonstrated that this 85‐kDa mannose‐rich glycoprotein component contained the SHP substrate‐1 for phosphotyrosine phosphatases and at least one other member of the signal‐regulatory protein (SIRP) family. The unusually high content of oligomannosidic carbohydrate moieties on these receptor‐like members of the immunoglobulin superfamily in neural tissue could be of functional significance for intercellular adhesion or signaling.