The Structure and Biosynthesis of Legume Seed Storage Proteins: A Biological Solution to the Storage of Nitrogen in Seeds

Abstract

This chapter discusses the structure and biosynthesis of legume seed storage. The importance of legume storage proteins as a major food protein resource world wide has always attracted a significant research effort by plant scientists. In addition, at various times, legume storage proteins or their encoding genes have been among the few plant experimental materials at the cutting edge of plant science research. Storage proteins can be isolated in large amounts from any commonly available legume seeds relatively easily and initially this enabled chemists to pioneer investigations into the chemical composition and gross characteristics of these proteins. Originally, it was technically only possible to isolate gene sequences as complementary DNAs (cDNA) and successful screening of a cDNA library often depended on the messenger RNA species being in high abundance as was the case with the storage proteins. The nutritional role of the storage proteins is reflected in their chemical composition and structure, and by the fact that they are made in large amounts. On germination, the storage proteins are broken down into their constituent amino acids, which are eventually resynthesized into the many proteins of the developing seedling before it achieves full autonomy. In general, up to 80% of the legume seed protein is made up of two distinct types of storage proteins, vicilin and legumin, which are salt-soluble at neutral pH.