Ricin and Ricinus communis agglutinin subunits are all derived from a single-size polypeptide precursor.
Antibodies have been raised in rabbits against the individually purified A and B subunits of the toxic castor bean lectin, ricin, and against the A' and B' subunits of Ricinus communis agglutinin type I. Each of the antisera recognised a single polypeptide species of Mr 60 500 when maturing castor bean endosperm mRNA was translated in vitro in a rabbit-reticulocyte-derived system. When dog pancreatic microsomal vesicles were included in the translational system, each subunit antiserum precipitated a group of 66 000-68 000-Mr core-glycosylated polypeptides which had been translocated into the lumen of the vesicles. The 60 500-Mr polypeptide appeared to be a common precursor to all four individual lectin subunits since (a) its glycosylated (66 000-68 000-Mr) forms were readily detected in the endoplasmic reticulum fraction isolated from maturing castor bean endosperm and (b) pulse-chase studies showed that the glycosylated precursors disappeared from the endoplasmic reticulum fraction with the concomittant appearance of authentic lectin subunits in a soluble protein fraction which included protein body matrix components. Antiserum prepared against whole R. communis agglutinin, type I, also precipitated the 65 000-Mr precursor in vitro and in vivo, but in addition precipitated a non-glycosylated 34 000-Mr polypeptide. This smaller protein is not a lectin subunit precursor, contradicting an earlier suggestion. It is most probably a precursor to the 2-S albumin storage proteins found in castor bean endosperm protein bodies.
D000118:Acetylglucosaminidase; D055598:Chemical Phenomena; D011232:Chemical Precipitation; D002621:Chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D007120:Immunochemistry; D037102:Lectins / Q000096:biosynthesis*; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D010446:Peptide Fragments / Q000096:biosynthesis; D037121:Plant Lectins; D014176:Protein Biosynthesis; D011498:Protein Precursors / Q000378:metabolism*; D012276:Ricin / Q000096:biosynthesis*
D037102:Lectins; D010446:Peptide Fragments; D037121:Plant Lectins; D011498:Protein Precursors; C017707:Ricinus communis agglutinin-1; D012276:Ricin; D000118:Acetylglucosaminidase; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase