POST-TRANSLATIONAL CLEAVAGE OF PROGLYCININ BY LEGUMATURAIN AND ITS PHYSIOLOGICAL SIGNIFICANCE

摘要

The 11S seed storage protein family is synthesized and assembled during a complex process that involved post-translational cleavage at an evolutionarily conserved asparagine-glycine bond by specific endoprotease [1,21,26], legumaturain or maturation enzyme [22]. To elucidate the action mechanism of legumaturain, physiological significance of the cleavage for the glycinin assembly, it is important to obtain a better understanding of the substrate-specificity, structural and conformational changes of the proprotein during the processing. For that purpose, we have constructed expression plasmid for glycinin pro A_(1α)B_(1b) and proA_5A_4B_3 precursors. These E. coli-expressed proteins are self-assembled into two molecular forms, giving apparent sedimentation coefficients of 7S and 11S. Both molecules were proved to be processed by legumaturain. By comparison of the sedimentation patterns of the components in sucrose gradients before and after cleavage, in the presence or without sodium chloride, we have found that post-translational cleavage affected the conformational changes of the proprotein and reduced its solubility. This, probably, is the main physiological function of the process that can be used for possible explanation of the mechanism for the deposition of the storage protein bodies in the cell.