Shotgun proteomic analysis of quinoa seeds reveals novel lysine-rich seed storage globulins

Quinoa seeds have high protein content and an exceptional balance of amino acids, with higher contents of lysine, methionine and cysteine than common cereals. To date, only three globulins, all of which have a content of lysine mass that does not exceed 3.8%, have been identified in quinoa. To address the protein present in quinoa seeds, TCA/Acetone protein extraction was performed using four different quinoa seed genotypes with contrasting edaphoclimatic origins. Proteins were identified and analyzed using label-free shotgun proteomics followed by in silico analysis, using the three published quinoa genomes. This analysis allowed us to identify sixteen globulins, thirteen of which are novel: nine legumin-like proteins and seven vicilin-like proteins. Seven of the novel proteins contain 7.5% or more of lysine mass, justifying the high content of lysine repeatedly reported in quinoa seeds. No significant differences were found between the four genotypes here analyzed.