A murrel cysteine protease, cathepsin L: bioinformatics characterization, gene expression and proteolytic activity

Abstract

Cathepsin L, a lysosomal endopeptidase, is a member of the peptidase C1 family (papain-like family) of cysteine proteinases that cleave peptide bonds of lysosomal proteins. In this study, we report a cathepsin L sequence identified from the constructed cDNA library of striped murrel Channa striatus (designated as CsCath L) using genome sequencing FLXTM technology. The full-length CsCath L contains three eukaryotic thiol protease domains at positions 134-145, 278-288 and 299-318. Phylogenetic analysis revealed that the CsCath L was clustered together with other cathepsin L from teleosts. The three-dimensional structure of CsCath L modelled by the I-Tasser program was compared with structures deposited in the Protein Data Bank to find out the structural similarity of CsCath L with experimentally identified structures. The results showed that the CsCath L exhibits maximum structural identity with pro-cathepsin L from human. The RNA fold structure of CsCath L was predicted along with its minimum free energy (−471.93 kcal/mol). The highest CsCath L gene expression was observed in liver, which was also significantly higher (P < 0.05) than that detected in other tissues taken for analysis. In order to investigate the mRNA transcription profile of CsCath L during infection, C. striatus were injected with fungus (Aphanomyces invadans) and bacteria (Aeromonas hydrophila) and its expression was up-regulated in liver at various time points. Similar to gene expression studies, the highest CsCath L enzyme activity was also observed in liver and its activity was up-regulated by fungal and bacterial infections.