Recombinant expression and characterization of lemon (Citrus limon) peroxidase

Background: Class III plant peroxidases play important role in a number of physiological processes in plants such as lignin biosynthesis, suberization, cell wall biosynthesis, reactive oxy-gen species metabolism and plant defense against pathogens. Peroxidases are also of significance in several industrial applications. In view of this, the production and identification of novel peroxi-dases having resistance towards temperature, pH, salts is desirable. Objective: The objective of the present work was to clone and characterize a novel plant peroxi-dase suitable for industrial application. Methods: A full length cDNA clone of lemon peroxidase was isolated using PCR and RACE ap-proaches, characterized and heterologously expressed in Escherichia coli using standard protocols. The expressed peroxidase was purified using Ni-NTA agarose column and biochemically characterized using standard protocols. The peroxidase was also in-silico characterized at nucleotide as well as protein levels using standard protocols. Results: A full length cDNA clone of lemon peroxidase was isolated and expressed heterologously in E. coli. The expressed recombinant lemon peroxidase (LPRX) was activated by in-vitro refold-ing and purified. The purified LPRX exhibited pH and temperature optima of pH 7.0 and 50°C, re-spectively. The LPRX was found to be activated by metal ions (Na⁺, Ca²⁺, Mg²⁺ and Mn²⁺) at lower concentration. The expressional analysis of the transcripts suggested involvement of lemon peroxi-dase in plant defense. The lemon peroxidase was in silico modelled and docked with the substrates guaiacol, and pyrogallol and shown the favourability of pyrogallol over guaiacol, which is in agree-ment with the in-vitro findings. The protein function annotation analyses suggested the involvement of lemon peroxidase in the phenylpropanoid biosynthesis pathway and plant defense mech-anisms. Conclusion: Based on the biochemical characterization, the purified peroxidase was found to be resistant towards the salts and thus, might be a good candidate for industrial exploitation. The in-sil-ico protein function annotation and transcript analyses highlighted the possible involvement of the lemon peroxidase in plant defense response.