Improving the catalytic behavior of inulin fructotransferase under high hydrostatic pressure

In situ and real-time insight into Rhizopus chinensis lipase under high pressure and temperature: Conformational traits and biobehavioural analysis

An in situ and real-time investigation was performed using an optical cell system and in-silico analysis to reveal the impacts of pressure and temperature on the conformational state and behaviours of Rhizopus chinensis lipase (RCL). The fluorescence intensity (FI) of RCL increased remarkably under high pressure, and part of this increase was recovered after depressurization. This result displayed the partially reversible conformational change of RCL, which may be associated with the local change of Trp224 near the catalytic centre. High temperature caused a significant loss of secondary structure, whereas the α-helical segments including the lid were preserved by high pressure even at temperatures over 60 °C. The parameters of enzymatic reaction monitored by UV showed that the hydrolysis rate was remarkably enhanced by the pressure of 200 MPa. In the pressure range of 0.1-200 MPa, the active volume measured by the in situ system decreased from -2.85 to -6.73 mL/mol with the temperature increasing from 20 °C to 40 °C. The high catalytic capacity of the lipase under high pressure and high temperature was primarily attributed to pressure protection on RCL.

Coupled effects of salt and pressure on catalytic ability of Rhizopus chinensis lipase

BACKGROUND

Both high pressure and environmental factors could influence the catalytic abilities of enzymes. This work investigated coupled effects of pressure and salts on Rhizopus chinensis lipase (RCL) to provide significant information for its further applications.

RESULTS

The maximum activity of RCL was observed under 200 MPa at 40 °C. The highest activity was achieved at concentrations of 0.06-0.1 mol L^-1 for tested salts. The effect of monovalent cations on RCL activity followed the Hofmeister series (K⁺ > Na⁺ > Li⁺ ) at 0.1 MPa but the order of Na⁺ and K⁺ was changed under 200 MPa. Meanwhile, the effects of anions did not follow the Hofmeister series. KCl slightly improved the thermostability of RCL at moderate concentration. At 60 °C, LiCl only stabilised RCL at 0.1 mol L^-1 . The pre-transition unfolding point was shifted from 4.5 to 3.5 mol L^-1 with pressure increasing from 0.1 to 600 MPa. In addition, KCl could not change the lipase's extrinsic fluorescence evolution versus pressure.

CONCLUSION

Pressure and salts could improve catalytic ability and stability of RCL under appropriate conditions. The effect of high pressure on RCL was influenced by salts. Meanwhile salts cannot prevent high pressure-induced damage to RCL. © 2017 Society of Chemical Industry.

Probing the Role of Two Critical Residues in Inulin Fructotransferase (DFA III-Producing) Thermostability from Arthrobacter sp. 161MFSha2.1

Inulin fructotransferase (IFTase) is an important enzyme that produces di-d-fructofuranose 1,2':2,3' dianhydride (DAF III), which is beneficial for human health. Present investigations mainly focus on screening and characterizing IFTase, including catalytic efficiency and thermostability, which are two important factors for enzymatic industrial applications. However, few reports aimed to improve these two characteristics based on the structure of IFTase. In this work, a structural model of IFTase (DFA III-producing) from Arthrobacter sp. 161MFSha2.1 was constructed through homology modeling. Analysis of this model reveals that two residues, Ser-309 and Ser-333, may play key roles in the structural stability. Therefore, the functions of the two residues were probed by site-directed mutagenesis combined with the Nano-DSC method and assays for residual activity. In contrast to other mutations, single mutation of serine 309 (or serine 333) to threonine did not decrease the enzymatic stability, whereas double mutation (serine 309 and serine 333 to threonine) can enhance thermostability (by approximately 5 °C). The probable mechanisms for this enhancement were investigated.