Primary structure and polymorphism of 2S albumins from seeds of Andean lupin (Lupinus mutabilis Sweet)

 2S albumins were isolated from seeds of Andean lupin (Lupinus mutabilis Sweet) by buffer extraction, ammonium sulphate precipitation and ultrafiltration followed ion-exchange and reversed-phase HPLC. The 2S albumin preparation (LM2S) contained eight albumins. The complete amino acid sequences of small and large subunits of three major albumins (LM2S-4, -5 and -6) were determined by automated Edman degradation of S-pyridylethylated polypeptides and peptides obtained from them by enzymatic digestions. The small subunit of the dominant 2S albumin (LM2S-4) contains 39 amino acid residues and has a molecular mass of 4731 Da. The large subunit of LM2S-4 contains 74 amino acid residues (molecular mass=8708 Da). Two 2S albumin isoforms (LM2S-4 and -6) are due to the expression of two distinct genes; LM2S-6 isoform has eight amino acid replacements when its sequence is compared with the sequence of LM2S-4. The LM2S-5 isoform contains an identical small subunit to LM2S-4, and has in comparison with LM2S-4 two additional amino acid residues at the N-terminus of the large subunit. The amino acid sequences of 2S isoforms from L. mutabilis showed high homology (78–83% identity) with 2S albumins from different Old World Lupinus species.