The Molecular Mass and Isoelectric Point of Plant Proteomes

Abstract

AbstractA proteomic analysis of proteomes from 145 plant species revealed apIrange of 1.99 (epsin) to 13.96 (hypothetical protein). The molecular mass of the plant proteins ranged from 0.54 to 2236.8 kDa. A putative Type-I polyketide synthase (22244 amino acids) inVolvox carteriwas found to be the largest protein in the plant kingdom and was not found in higher plant species. Titin (806.46 kDa) and misin/midasin (730.02 kDa) were the largest proteins identified in higher plant species. ThepIand molecular weight of the plant proteome exhibited a trimodal distribution. An acidicpI(56.44% of proteins) was found to be predominant over a basicpI(43.34% of proteins) and the abundance of acidicpIproteins was higher in unicellular algae species relative to multicellular higher plants. In contrast, the seaweed,Porphyra umbilicalis, possesses a higher proportion of basicpIproteins (70.09%). Plant proteomes were also found to contain the amino acid, selenocysteine (Sec), which is the first report of the presence of this amino acid in plants. Additionally, plant proteomes also possess ambiguous amino acids Xaa (unknown), Asx (asparagine or aspartic acid), Glx (glutamine or glutamic acid), and Xle (leucine or isoleucine) as well.