|Coe Jr, Edward|
Submitted to: Encyclopedia of Genetics
Publication Type: Review Article
Publication Acceptance Date: May 17, 2000
Publication Date: N/A
Technical Abstract: More than 70% of the proteins consumed by humans are derived from storage proteins of legume and cereal seeds. Seed protein content of legumes varies from 20 to 40%, while in cereals it accounts for 7-15% of the dry weight of the seed. Seed storage proteins accumulate in the cotyledon and embryo of dicotyledonous plants and in the endosperm of monocotyledonous plants. These proteins are deposited in specialized membrane-bound organelles called protein bodies. The predominant legume storage proteins are salt-soluble globulins and are grouped under two classes, 7S and 11S, while the major storage proteins of cereals are the alcohol-soluble prolamins. Exceptions are oats and rice, in which the major storage proteins are globulin-like. Because of the abundance of these proteins, they are mainly responsible for the nutritional quality of the human diet. The deficiency of certain essential amino acids in the seed proteins may, however, limit their nutritional quality for monogastric animals. In general the cereal storage proteins are deficient in lysine, threonine, and tryptophan while the cereal prolamins contain low levels of cysteine and methionine. Most of the seed storage proteins are encoded by multi-gene families. The cereal prolamins appear to have evolved from a single ancestral gene and similarly, the 7S and 11S legume proteins appear to have evolved from a common ancestral protein. The synthesis of seed storage protein is primarily controlled at the level of transcription, but may also be subject to post-transcriptional controls. The transcription of seed protein genes is highly regulated in a spatial and temporal manner.