Endogenous lectin from cultured soybean cells: exposure of the SB-1 lectin on the cell wall.
Digestion of seed soybean agglutinin with V-8 protease yielded seven distinct fragments (Mr 10,000-20,000) that were well-resolved by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Each individual peptide (F1 through F7) was isolated; determination of the amino acid sequence at the NH2-terminal portion of each peptide established its position in the intact polypeptide of soybean agglutinin. The isolated peptides were used as affinity adsorbents to obtain antibodies that bound individual fragments (anti-F1 through anti-F7). These antibody preparations were, in turn, used in immunofluorescence staining of intact cultured soybean (SB-1) cells. Only those antibody preparations that bind to the NH2-terminal portion (residues 1-124) of the intact soybean agglutinin showed significant cell surface labeling. In contrast, the antibody preparations that bound to residues 125-253 failed to bind to intact SB-1 cells. These results suggest that the SB-1 lectin has the NH2-terminal portion of the polypeptide chain exposed and accessible at the cell surface, while the COOH-terminal portion of the same molecule may be masked, either through protein folding or through embedding in the cell wall. Limited digestion of the cell wall polysaccharides by cellulase or pectinase released the majority of the cell surface lectin.
Malek-Hedayat
S
S
Department of Biochemistry, Michigan State University, East Lansing 48824.
Wang
J L
JL
Schindler
M
M
D000906:Antibodies / Q000276:immunology; D002473:Cell Wall / Q000032:analysis / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D037102:Lectins / Q000032:analysis* / Q000378:metabolism; D010446:Peptide Fragments / Q000032:analysis / Q000276:immunology; D037121:Plant Lectins; D012697:Serine Endopeptidases / Q000494:pharmacology; D030262:Soybean Proteins; D013025:Glycine max / Q000032:analysis / Q000166:cytology* / Q000378:metabolism; D010835:Phytohemagglutinins
D000906:Antibodies; D037102:Lectins; D010446:Peptide Fragments; D037121:Plant Lectins; D012697:Serine Endopeptidases; D030262:Soybean Proteins; C028824:soybean lectin; D010835:Phytohemagglutinins; C028344:glutamyl endopeptidase