Biochemical and immunological comparisons of carbohydrate-binding protein 35 and an IgE-binding protein.
The predicted amino acid sequence of carbohydrate-binding protein 35 (CBP35; Mr approximately 35,000), a galactose-specific lectin in many mouse and human cells, has been compared to the predicted sequence of an IgE-binding protein (epsilon BP) originally identified in rat basophilic leukemia cells. The sequences of the two proteins showed that: (a) 85% of the amino acid residues are identical; (b) the polypeptide chains are comprised of two distinct domains; and (c) highly conserved internal repetitive sequences are present. Consistent with these observations, antisera raised against CBP35 or against a synthetic peptide derived from the epsilon BP sequence cross-reacted with both proteins. Moreover, fractionation of extracts of mouse 3T3 fibroblasts over an IgE-Sepharose affinity column showed that CBP35 bound to IgE; this binding was reversed by addition of lactose. Conversely, fractionation of extracts of rat basophilic leukemia cells over an affinity column of Sepharose derivatized with N-(epsilon-amino-caproyl)-D-galactosamine showed that epsilon BP was a galactose-binding protein. Furthermore, epsilon BP bound to IgE-Sepharose could be eluted by lactose. Finally, transcription and translation in vitro of the cDNA corresponding to epsilon BP yielded a polypeptide containing carbohydrate-binding activity. All of these results strongly support the conclusion that CBP35 and epsilon BP are mouse and rat homologues, respectively.
Laing
J G
JG
Department of Biochemistry, Michigan State University, East Lansing 48824.
Robertson
M W
MW
Gritzmacher
C A
CA
Wang
J L
JL
Liu
F T
FT
D000818:Animals; D000944:Antigens, Differentiation, B-Lymphocyte / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002478:Cells, Cultured; D006801:Humans; D015151:Immunoblotting; D007073:Immunoglobulin E / Q000378:metabolism; D008970:Molecular Weight; D014176:Protein Biosynthesis; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011961:Receptors, Fc / Q000235:genetics / Q000378:metabolism*; D017455:Receptors, IgE; D014158:Transcription, Genetic
D000944:Antigens, Differentiation, B-Lymphocyte; D002352:Carrier Proteins; D011956:Receptors, Cell Surface; D011961:Receptors, Fc; D017455:Receptors, IgE; C055213:saccharide-binding proteins; D007073:Immunoglobulin E