32. Thermostable Proteases

Proteases are one of the largest selling enzymes in the world. This is rationalised by their extensive usage in the detergent, food, pharmaceutical, leather and textile industries. Thermostability in industrial enzymes remains a desirable attributes for (1) achieving faster conversion rates, (2) greater catalytic efficiencies and (3) protection from microbial contamination while operating at higher temperatures. Proteases endowed with such characteristics are all the more needed for baking and textile processing. In general, most of the industrial proteases are sourced from Bacillus sp. Thermostability in protease is accorded by protein engineering or appropriate immobilisation methods. Proteases from hyperthermophiles and thermophiles are natural choice for exploring the inherent heat stability. Few classical thermostable proteases especially those from Pyrococcus and Thermococcus have generated considerable interest. Heat stability in these cases has been attributed to large proportion of hydrophobic residue, extensive hydrogen bonding and increased share of disulphide bonds. Extensive screening of large range of unexplored thermophiles is well called for. Understanding their protein architecture may enable rationale design for heat-stable proteases in future.

This chapter highlights the enzymatic characteristics and novel properties of known thermostable proteases and focuses on their structure–function relationship. Recent developments and future perspectives in screening new proteases from hyperthermophiles/thermophiles, metagenomic studies, directed evolution, site-directed mutagenesis, modern immobilisation methods such as CLEC, CLEA and PCMC and immobilisation on nanoparticles are comprehensively covered.