Title: Enhancing the stability of a carboxylesterase by entrapment in chitosan coated alginate beads Raghu S, Pennathur G Ref: Turk J Biol, 42:307, 2018 : PubMed
A carboxylesterase isolated from Aeromonas caviae MTCC 7725 was immobilized by entrapping it in chitosan coated calcium alginate beads. This was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and Fourier transform infrared spectroscopy (FTIR). The activity of the native and immobilized enzyme was measured at various temperatures, pH levels, and organic solvents. The optimum temperature for activity of the native enzyme was found to be 40 degrees C and this increased to 50 degrees C on immobilization. The immobilized enzyme showed enhanced stability and high residual activity in various organic solvents as compared to the free enzyme. An environmentally benign approach was used for the synthesis of ethyl salicylate using the immobilized enzyme. The product obtained was confirmed by GC-MS. The kinetic parameters, such as K m and Vmax, were also determined for the native and immobilized enzyme. The immobilized enzyme retained 50% of its activity after vfie cycles. The immobilized enzyme retained 80% and 40% of its activity at 4 degrees C and at 37 degrees C, respectively, at the end of 40 days. The results obtained from our study show that the immobilized enzyme can serve as a robust catalyst for industrial applications.
        
Title: Understanding domain movements and interactions of Pseudomonas aeruginosa lipase with lipid molecule tristearoyl glycerol: A molecular dynamics approach Thiruvengadam K, Baskaran SK, Pennathur G Ref: J Mol Graph Model, 85:190, 2018 : PubMed
Lipases are biocatalysts which exhibit optimal activity at the aqueous-lipid interface. Molecular Dynamics (MD) Simulation studies on lipases have revealed the structural changes occurring in the enzyme, at the loop-helix-loop, often designated as the "lid", which is responsible for its interfacial activation. In recent years, MD simulation of lipases at molecular level have been studied in detail, whereas very few studies are carried over on its interaction with lipid molecules. Hence, in the current study we have investigated molecular interaction of bacterial lipase (Pseudomonas aeruginosa lipase, PAL) with a lipid molecule (tristearoyl glycerol, TGL). This provides an insight into the interfacial activation of the enzyme. The lipid molecule was placed near the lids of the enzyme and MD simulations were performed for 100 ns to understand the nature and site of the interaction. The results clearly indicate that, the presence of a lipid molecule near the lids affects the motion of the enzyme through changes in conformation. Lipid molecule near the lids reduces the movements of both lids, and the TGL molecule was observed moving towards the active site. The movement of the lids, surface accessibility and the domain movements of PAL are discussed and the results provide valuable insight in to the role played by the two lids in the interfacial activation of PAL with TGL.
Mammalian gastric lipases are stable and active under acidic conditions and also in the duodenal lumen. There has been considerable interest in acid stable lipases owing to their potential application in the treatment of pancreatic exocrine insufficiency. In order to gain insights into the domain movements of these enzymes, molecular dynamics simulations of human gastric lipase was performed at an acidic pH and under neutral conditions. For comparative studies, simulation of dog gastric lipase was also performed at an acidic pH. Analyses show, that in addition to the lid region, there is another region of high mobility in these lipases. The potential role of this novel region is discussed.
Pseudomonas aeruginosa lipase is a 29-kDa protein that, following the determination of its crystal structure, was postulated to have a lid that stretched between residues 125 and 148. In this paper, using molecular dynamics simulations, we propose that there exists, in addition to the above-mentioned lid, a novel second lid in this lipase. We further show that the second lid, covering residues 210-222, acts as a triggering lid for the movement of the first. We also investigate the role of hydrophobicity in the movement of the lids and show that two residues, Phe214 and Ala217, play important roles in lid movement. To our knowledge, this is the first time that a double-lid movement of the type described in our manuscript has been presented to the scientific community. This work also elucidates the interplay of hydrophobic interactions in the dynamics, and hence the function, of an enzyme.