Post-translational cleavage pattern of Lupinus angustifolius γ-conglutin

Protein post-translational modifications are a key element for the functional diversity of the proteome. The modifications generally refer to the addition of functional groups to certain proteins; however, proteolytic cleavage is also one of the relevant events during protein maturation. γ-Conglutin is a unique protein fraction present in lupin seeds that is marked by numerous unusual properties. This protein fraction undergoes very complex post-translational maturation. Unfortunately, the precise mechanism of γ-conglutin post-translational processing is not yet fully understood.

Two independent methods were used to study γ-conglutin post-translational cleavage processing. Edman N-terminal sequencing indicates that the signal peptide is processed at Tyr34, while α- and β-subunit cleavage takes place between Ser295 and Ser296. High-resolution mass spectrometry revealed a great diversity of N-terminal sequences of γ-conglutin α-subunit. However, most abundant peptides also began from Tyr34. Mass spectrometric analyses additionally confirmed the subunit cleavage position between two serine residues.

The results indicate that the proteolytic processing of γ-conglutin signal peptide is not precise. On the other hand, the post-translational cleavage between α- and β-subunits of γ-conglutin is very conserved. Interestingly, the results also indicate that proteolytic processing leading to the formation of two subunits of γ-conglutin is incomplete, leaving a certain amount of the protein in an uncut form. © 2018 Society of Chemical Industry.