Tuesday, November 6, 2007 - 12:30 PM
166-5
Engineering Proteins for Improved Nutritional Value.
Gururaj, A. Rao, Iowa State University, 4212 MBB, Iowa State University, Ames, IA 50011
Proteins are essential components of a healthy diet in both humans and animals. However, both species lack the ability to synthesize essential amino acids and these have to be supplied through external dietary sources such as cereal grains and legume seeds. Compared to animal proteins such as meat and milk, however, cereals and legumes are generally deficient in essential amino acids such as lysine and methionine. This can be a serious limitation especially in an exclusively vegetarian diet. On the agricultural front, the consequence is that feed mixtures, which consist predominantly of cereals and legumes, must be supplemented with essential amino acids at a cost of hundreds of millions of dollars. Over the years plant breeders have attempted to select cultivars and alter levels of quality proteins through classical breeding. In parallel, free amino acid levels have been increased by manipulation of biosynthetic pathways. Furthermore, advances in recombinant DNA technology and plant transformation protocols have allowed the modification of endogenous genes to include codons for deficient or absent amino acids. An alternative is to express heterologous proteins rich in desired amino acids. However, the generality of the approach by which foreign proteins rich in desired amino acids may be introduced is constrained further by the small number of suitable heterologous proteins. An appealing solution to this problem is to artificially increase the essential amino acid content of a given protein through knowledge-based, site-directed mutagenesis, paying close attention to the proper folding and stability of the engineered protein. This presentation will provide an overview of the above approaches and especially highlight the success of protein engineering for nutritional enhancement.