The role of proteolysis in the processing and assembly of 11S seed globulins.
11S seed storage proteins are synthesized as precursors that are cleaved post-translationally in storage vacuoles by an asparaginyl endopeptidase. To study the specificity of the reaction catalyzed by this asparaginyl endopeptidase, we prepared a series of octapeptides and mutant legumin B and G4 glycinin subunits. These contained amino acid mutations in the region surrounding the cleavage site. The endopeptidase had an absolute specificity for Asn on the N-terminal side of the severed peptide bond but exhibited little specificity for amino acids on the C-terminal side. The ability of unmodified and modified subunits to assemble into hexamers after post-translational modification was evaluated. Cleavage of subunits in trimers is required for hexamer assembly in vitro. Products from a mutant gene encoding a noncleavable prolegumin subunit (LeBDeltaN281) accumulated as trimers in seed of transgenic tobacco, but products from the unmodified prolegumin B gene accumulated as hexamers. Therefore, the asparaginyl endopeptidase is required for hexamer assembly.
Jung
R
R
United States Department of Agriculture-Agricultural Research Service and the Departments of Agronomy and Biochemistry, Purdue University, West Lafayette, Indiana 47907, USA.
Scott
M P
MP
Nam
Y W
YW
Beaman
T W
TW
Bassüner
R
R
Saalbach
I
I
Müntz
K
K
Nielsen
N C
NC
D003546:Cysteine Endopeptidases / Q000378:metabolism*; D005916:Globulins / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D009154:Mutation; D009842:Oligopeptides / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D012639:Seeds / Q000378:metabolism; D013025:Glycine max / Q000201:enzymology / Q000378:metabolism*; D013379:Substrate Specificity; D014170:Transformation, Genetic; D000099240:Asparaginyl Endopeptidase
D003546:Cysteine Endopeptidases; D005916:Globulins; D009842:Oligopeptides; D010940:Plant Proteins; D000099240:Asparaginyl Endopeptidase