Isolation, identification, and stability of Ficin 1c isoform from fig latex

Latex of common fig ( Ficus carica ) is a rich protein source with a high level of proteolytic activity contributing to its defensive role. The divergent group of cysteine proteases known as ficin (EC 3.4.22.3) represents the majority of latex protein content and shows activity towards fig parasites. Both classical and novel biochemical techniques suggest the intricate pattern of ficin expression and activity profiles. Even though structurally related, different ficin isoforms show some differences in pI values enabling their separation using ion-exchangers. A single alkaline isoform was purified and identified based on the available transcriptomic data as Ficin 1c. This isoform shows both general proteolytic and gelatinolytic activity suggesting a biological role in the degradation of a broad range of natural substrates. The insight into the Ficin 1c structure also provided some functional clues. The secondary structure content and the overall fold are similar to related proteases of the same and other plant sources resulting in similar unfolding routes. Stability assessment of Ficin 1c in comparison to ficin isoform mixture showed that isoform diversity might lead to increased protease stability. Purified alkaline ficin isoform, identified as Ficin 1c regarding fig transcriptome, shows decreased stability compared to the ficin isoform mixture.