Chickpea (Cicer arietinum L.) seed proteins show a lot of functional properties leading this legume to be an interesting component for the development of protein-enriched foods. However, both the in-depth proteomic investigation and structural characterization of chickpea seed proteins are still lacking. In this paper a detailed characterization of chickpea seed protein fraction by means of SDS-PAGE, in-gel protein digestion, high-resolution mass spectrometry, and database searching is reported. Through this approach, twenty SDS gel bands were cut and analyzed. While the majority of the bands and the identified peptides were related to vicilin and legumin storage proteins, metabolic functional proteins were also detected. Legumins, as expected, were revealed at 45-65 kDa, as whole subunits with the α- and β-chains linked together by a disulphide bond, but also at lower mass ranges (α- and β-chains migrating alone). Similarly, but not expected, the vicilins were also spread along the mass region between 65 and 23 kDa, with some of them being identified in several bands. An MS structural characterization allowed to determine that, although chickpea vicilins were always described as proteins lacking cysteine residues, they contain this amino acid residue. Moreover, similar to legumins, these storage proteins are firstly synthesized as pre-propolypeptides (Mr 50-80 kDa) that may undergo proteolytic steps that not only cut the signal peptides but also produce different subunits with lower molecular masses. Overall, about 360 different proteins specific of the Cicer arietinum L. species were identified and characterized, a result that, up to the current date, represents the most detailed description of the seed proteome of this legume.
Keywords: Orbitrap® mass spectrometry; SDS-PAGE; chickpea proteins; legumins; vicilins.