Properties, biosynthesis and processing of a sulfur-rich protein in Brazil nut (Bertholletia excelsa H.B.K.).
An abundant seed protein, which is exceptionally rich in the sulfur-containing amino acids, methionine (18%) and cysteine (8%), is synthesized in Brazil nut embryos about 9 months after flowering. This sulfur-rich protein consists of two low-molecular-mass polypeptide components, a 9-kDa polypeptide and a 3-kDa polypeptide. The two-subunit polypeptides associate through disulfide linkage(s) to form a 12-kDa protein molecule. We have demonstrated through in vitro translation studies, using RNA from 9-month-old embryos, that the sulfur-rich protein is synthesized as a larger precursor polypeptide of 18 kDa. In addition, data from in vivo labelling studies of 9-month-old Brazil nuts suggest that there are two intermediate precursors of the sulfur-rich protein, one of 15 kDa and another of 12 kDa. One of these precursors, the 12-kDa polypeptide, accumulates for a 2-month period in the developing embryos. From these data we infer that at least three stepwise cleavages are involved in the maturation of the sulfur-rich protein from its 18-kDa precursor.
D000603:Amino Acids, Sulfur / Q000032:analysis; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D007120:Immunochemistry; D009754:Nuts / Q000032:analysis*; D010455:Peptides / Q000032:analysis; D010940:Plant Proteins / Q000096:biosynthesis* / Q000378:metabolism; D011499:Protein Processing, Post-Translational
D000603:Amino Acids, Sulfur; D010455:Peptides; D010940:Plant Proteins