Structural insights into the substrate specifi city of two esterases from the thermophilic Rhizomucor miehei

Abstract

Two hormone-sensitive lipase (HSL) family esterases ( Rm EstA and Rm EstB) from the thermophilic fungus Rhizomucor miehei , exhibiting distinct substrate specifi city, have been recently reported to show great potential in industrial applications. In this study, the crystal structures of Rm EstA and Rm EstB were determined at 2.15 Å and 2.43 Å resolutions, respectively. The structures of Rm EstA and Rm EstB showed two distinctive domains, a catalytic domain and a cap domain, with the classical α hydrol;ase fold. Catalytic triads consisting of residues Ser161, Asp262, and His292 in Rm EstA, and Ser164, Asp261, and His291 in Rm EstB were found in the respective canonical positions. Structural comparison of Rm EstA and Rm EstB revealed that their distinct substrate specifi city might be attributed to their different substrate-binding pockets. The aromatic amino acids Phe222 and Trp92, located in the center of the substrate-binding pocket of Rm EstB, blocked this pocket, thus narrowing its catalytic range for substrates (C2C8). Two mutants (F222A and W92F in Rm EstB) showing higher catalytic activity toward long-chain substrates further confi rmed the hypothesized interference. This is the fi rst report of HSL family esterase structures from fi lamentous fungi.jlr The information on structure-function relationships could open important avenues of exploration for further industrial applications of esterases.