Seed Storage Globulins: Origin and Evolution of Primary and Higher Order Structures

Area of Science:

• Plant biochemistry
• Molecular evolution
• Protein structure and function

Background:

• Legumin and vicilin are two-domain seed storage globulins.
• They share structural similarities with plant germins and bacterial oxalate decarboxylases.
• Independent evolutionary paths link storage globulins and germins to bacterial oxalate decarboxylases.

Purpose of the Study:

• To investigate the evolutionary origins of seed storage globulins.
• To elucidate the mechanism of legumin and vicilin degradation during seed germination.
• To understand the structural basis for controlled proteolysis.

Main Methods:

• Comparative analysis of primary and tertiary structures.
• In vitro and in vivo limited proteolysis experiments.
• Analysis of subunit interactions and cleavage patterns.

Main Results:

• Legumin structures retain ancient features more than vicilin.
• Limited proteolysis initiates a regular, one-by-one degradation of storage globulin molecules.
• Proteolysis loosens legumin's intersubunit interactions, suggesting dissociation triggers degradation.

Conclusions:

• Seed storage globulins evolved from bacterial oxalate decarboxylases through independent pathways.
• A specific degradation mechanism involving one-by-one cleavage has evolved for storage globulins.
• Legumin degradation is hypothesized to be initiated by dissociation of its oligomeric structure.