Heterologous Expression of Legumin Gene in E. coli Isolated from cDNA Clones of Immature Seeds of Pigeonpea (Cajanus cajan L.)

Proteins are one of the targets for improving the nutritional quality, and attempts are being made through manipulation of its native gene(s). Pigeonpea (Cajanus cajan L.) is one of the nutritionally important legumes of tropical and subtropical regions of the world, and studies of the structure of seed storage proteins and their interactions have been limited by the difficulty of isolating single-protein subunits in large amounts from a complex mixture of the seed endosperm. One way to overcome this problem is the expression of seed storage protein-encoded gene(s) in heterologous systems that have additional advantages wherein specific gene modifications can be made and the new gene constructs can quickly be expressed. Legumin protein was extracted from pigeonpea seeds of different developmental stages (5th to 25th day after flowering [DAF]) and characterized. The legumin gene (leg) of size 1.482 kb was screened, using the deoxygenin-labeled legumin probe, from the complementary deoxyribonucleic acid (cDNA) library, constructed from 18-day-old (DAF) immature seeds of pigeonpea and sequenced (accession no. AF3555403). The legumin gene was further characterized by DNA blotting, and its probable secondary structure was predicted using online ExPASy server. Significant Protein Data Bank (PDB) alignment of the deduced legumin protein by BLASTP was observed with proglycinin of soybean. Comparative 3D structural homology was predicted by Cn3D software, and the legumin protein showed the 3D structure alignment and interaction homology with proglycinin chain 1FXZA (PDB no. 1FXZ). The legumin gene was subcloned in vector pET-24a driven by the bacterial promoter, and its expression was detected in Escherichia coli by immunoblotting using polyclonal antibodies, raised against the purified legumin protein.