Seed Storage Protein Deficiency Improves Sulfur Amino Acid Content in Common Bean (Phaseolus vulgarisL.): Redirection of Sulfur from γ-Glutamyl-S-methyl-cysteine

Abstract

The contents of sulfur amino acids in seeds of common bean ( Phaseolus vulgaris L.) are suboptimal for nutrition. They accumulate large amounts of a gamma-glutamyl dipeptide of S-methyl-cysteine, a nonprotein amino acid that cannot substitute for methionine or cysteine in the diet. Protein accumulation and amino acid composition were characterized in three genetically related lines integrating a progressive deficiency in major seed storage proteins, phaseolin, phytohemagglutinin, and arcelin. Nitrogen, carbon, and sulfur contents were comparable among the three lines. The contents of S-methyl-cysteine and gamma-glutamyl-S-methyl-cysteine were progressively reduced in the mutants. Sulfur was shifted predominantly to the protein cysteine pool, while total methionine was only slightly elevated. Methionine and cystine contents (mg per g protein) were increased by up to ca. 40%, to levels slightly above FAO guidelines on amino acid requirements for human nutrition. These findings may be useful to improve the nutritional quality of common bean.

Effects of proteome rebalancing and sulfur nutrition on the accumulation of methionine rich δ-zein in transgenic soybeans

“…Sulfur nutrition or methionine supplementation has been shown to influence the accumulation of methionine-rich storage proteins in legumes (Chiaiese et al, 2004; Amira et al, 2005). Common bean ( Phaseolus vulgaris L.) accumulates large amounts of a γ-glutamyl dipeptide of S-methyl-cysteine, a non-protein amino acid (Taylor et al, 2008). Interestingly, the removal of 7S globulin and phytohemagglutinin in Phaseolus vulgaris enhanced the accumulation of sulfur-rich proteins (Marsolais et al, 2010).…”

Arabidopsis mutants lacking asparaginases develop normally but exhibit enhanced root inhibition by exogenous asparagine

“…Elemental analysis was performed by dry combustion with a LECO CNS-2000 Elemental Analyzer on approximately 40 mg dry seed samples as described by Taylor et al (2008).…”

“…Free and total amino acids were quantified from 50 mg seed samples as previously described (Taylor et al 2008). For quantification of Asn in roots, tissue was harvested, rinsed with water, blotted and weighed.…”

Phaseolin diversity as a possible strategy to improve the nutritional value of common beans (Phaseolus vulgaris)

“…Recently, Taylor et al (2008) evaluated the overall AA composition of genetically related lines of common beans deficient in selected seed storage proteins (phaseolin, phytohemagglutinin and/ or arcelin). They found several changes in the free AA content in bean lines deficient in storage proteins, including a reduction of S-methyl-cysteine and c-glutamyl-S-methyl-cysteine (a non-protein AA that cannot substitute the requirements of methionine or cysteine in the diet).…”

“…Attempts have been made to improve the protein quality of the common bean through breeding programs or genetic manipulation (Aragao et al, 1999;Gepts & Bliss, 1984;Taylor, Chapman, Beyaert, Hernandez, & Marsolais, 2008). The principal target has usually been phaseolin, since it is the main storage protein in seeds and makes up a high and variable (30-50%) proportion of the total protein and despite the fact that phaseolin is deficient in methionine, cysteine and tryptophan.…”