Characterization of a novel thermostable phospholipase C from T. kodakarensis suitable for oil degumming

Enhancing the Thermostability of Phospholipase C by Structural-Based Proline Incorporation to Improve Its Degumming Performance

Thermostability can be improved by introducing prolines into targeted sites, enhancing enzyme performance in specific reactions. In our present study, a novel fungal phospholipase C derived from Talaromyces islandicus (TiPLC) was first heterologously expressed in Pichia pastoris and biochemically characterized. Given the poor thermal stability of TiPLC, a structure-based proline incorporation strategy was used to enhance its thermostability further. Two single-site (E92P and A375P) mutants were selected from seven designs, exhibiting improved stability while retaining wild-type's basic properties (optimum reaction pH and temperature). Compared to the wild-type, the t1/2 of E92P and A375P under 40 °C extended by 1.62 and 1.27 times, respectively. Meanwhile, the E92P and A375P mutants exhibited a 20% increase in activity using p-NPPC as substrate. Moreover, double mutant E92P-A375P exhibited 2.43 times enhancement compared to the wild-type. Results of the oil degumming experiment further confirmed that the double mutant significantly improved the performance of TiPLC, with a reduction in residual phosphorus to 78 ppm, while for the wild-type, the residual phosphorus was 131 ppm under the same reaction. Molecular simulations indicated that proline incorporation into 92 and 375 sites significantly improved the rigidity of partial flexible regions, thus contributing to the increased thermostability.

Thermal Stabilization of a Bacterial Zn(II)-Dependent Phospholipase C through Consensus Sequence Design

Proteins' extraordinary performance in recognition and catalysis has led to their use in a range of applications. However, proteins obtained from natural sources are oftentimes not suitable for direct use in industrial or diagnostic setups. Natural proteins, evolved to optimally perform a task in physiological conditions, usually lack the stability required to be used in harsher conditions. Therefore, the alteration of the stability of proteins is commonly pursued in protein engineering studies. Here, we achieved a substantial thermal stabilization of a bacterial Zn(II)-dependent phospholipase C by consensus sequence design. We retrieved and analyzed sequenced homologues from different sources, selecting a subset of examples for expression and characterization. A non-natural consensus sequence showed the highest stability and activity among those tested. Comparison of the stability parameters of this stabilized mutant and other natural variants bearing similar mutations allows us to pinpoint the sites most likely to be responsible for the enhancement. Point mutations in these sites alter the unfolding process of the consensus sequence. We show that the stabilized version of the protein retains full activity even in harsh oil degumming conditions, making it suitable for industrial applications.

Sustainable Refining of Vegetable Oil Made Easy with a Designer Phospholipase C Enzyme

The increasing demand pressures the vegetable oil industry to develop novel refining methods. Degumming with type C phospholipases (PLCs) is a green technology and provides extra oil. However, natural PLCs are not active under the harsh conditions used in oil refining plants, requiring additional unit operations. These upfront capital expenditures and the associated operational costs hinder the adoption of this method. Here, we present a process based on ChPLC, a synthetic PLC obtained by consensus sequence design, possessing superior thermal stability and catalytic properties. Using ChPLC, crude soybean oil degumming was completed at 80 °C in 30 min, the temperature and residence time imposed by the design of existing oil refining plants. Remarkably, an extra yield of oil of 2% was obtained using 60% of the dose recommended for PLCs marketed today, saving upfront investments and reducing the operational cost of degumming. A techno-economic analysis indicates that, for medium size plants, ChPLC reduces the overall cost of soybean oil enzymatic degumming by 58%. The process presented here facilitates the implementation of enzymatic technologies to oil producers, regardless of their processing capacity, bringing potential annual benefits in the billion-dollar range for the global economy.