Thermus thermophilus as a Source of Thermostable Lipolytic Enzymes

Abstract

Lipolytic enzymes, esterases (EC 3.1.1.1) and lipases (EC 3.1.1.3), catalyze the hydrolysis of ester bonds between alcohols and carboxylic acids, and its formation in organic media. At present, they represent about 20% of commercialized enzymes for industrial use. Lipolytic enzymes from thermophilic microorganisms are preferred for industrial use to their mesophilic counterparts, mainly due to higher thermostability and resistance to several denaturing agents. However, the production at an industrial scale from the native organisms is technically complicated and expensive. The thermophilic bacterium Thermus thermophilus (T. thermophilus) has high levels of lipolytic activity, and its whole genome has been sequenced. One esterase from the T. thermophilus strain HB27 has been widely characterized, both in its native form and in recombinant forms, being expressed in mesophilic microorganisms. Other putative lipases/esterases annotated in the T. thermophilus genome have been explored and will also be reviewed in this paper.

Keywords: Thermus thermophilus; esterase; lipase; lipolytic; thermophilic.

Figure 1

Bacterial lipolytic enzymes that represent new families or subfamilies added to the classification of Arpingy and Jaeger and discovered by metagenomics.

Figure 2

(A) Representation of the secondary structure of the α/β hydrolase fold showing the residues involved in catalysis. α helices and β strands are shown as arrows and boxes, respectively, black dots represent the residues of the catalytic triad. (B) Crystallographic structure of the carboxylesterase Est30 from Geobacillus stearothermophilus (PDB ID:1TQH) showing a modified α/β hydrolase core with a seven-stranded β sheet and a cap domain comprising three alpha helices. The ribbon diagram is colored yellow for β strands, red for α helices and green for loops. Residues of catalytic triad are shown as sticks in blue.

Figure 3

Examples of applications of lipase/esterase catalyzed reactions: (A) production of geranyl acetate ; (B) enantiopure secondary alcohols and (C) biodiesel.

Figure 4

Scheme of predicted proteins from T. thermophilus HB27 (genome reference NC005835) studied hitherto to analyze its lipolytic activity and type of assay used. Boxes in dark blue correspond to the proteins identified to be mainly responsible for the lipolytic activity in T. thermophilus HB27. Boxes using former nomenclature (YP 005247 and YP 005054, genome reference AE017221) correspond to records that have been removed after the recent genome annotations update.