Cloning, Characterization, and Structural Modeling of an Extremophilic Bacterial Lipase Isolated from Saline Habitats...

Lipases have a characteristic folding pattern of α/β-hydrolase with mostly parallel β-sheets, flanked on both sides by α-helixes in the structure. The active site is formed by a catalytic triad (serine, aspartic/glutamic acid, and histidine), which is highly conserved. In this study, we have used an integrated experimental and computational approach to identify the extremophilic microbial lipases from the saline habitats of the Thar Desert of Rajasthan. Lipase-producing bacteria were screened and a few samples showed significant lipase activity in both quantitative and qualitative experiments. 16S rRNA sequence analysis of the isolate F1 showed that its sequence is quite similar to that of Bacillus licheniformis and Bacillus haynesii, indicating that this isolate belongs to a new subspecies of Bacillus. The isolate F7 showed maximum sequence identity with Bacillus tequilensis strain 10b. The isolate F7 sequence analysis provided a clear testimony that it can be a new strain of Bacillus tequilensis. The F7 lipase exhibited optimal activity at 60 °C and pH 9. Structural modeling of the F7 lipase revealed that it has a highly conserved alpha/beta hydrolase fold at the sequence and structural level except for the N-terminal region. Interestingly, residue Glu128 was different from the template structure and showed the hydrogen bonding between the side chain of Glu128 and side chains of Asn35 and Gln152 amino acids. Besides, this amino acid also showed salt bridge interaction between Glu128--Lys101. These interactions may be assisting in preserving the stability and activity of lipase at high temperatures and in alkaline pH conditions. The information gathered from this investigation will guide in the rational designing of new more potential extremophilic lipase.