Replacement of Pregastric Lipases in Cheese Production: Identification and Heterologous Expression of a Lipase from Pleurotus citrinopileatus

Characterization of a GDS(L)-like hydrolase from Pleurotus sapidus with an unusual SGNH motif

The GDS(L)-like lipase from the Basidiomycota Pleurotus sapidus (PSA_Lip) was heterologously expressed using Trichoderma reesei with an activity of 350 U L-1. The isoelectric point of 5.0 was determined by isoelectric focusing. The novel PSA_Lip showed only 23.8-25.1%, 25.5%, 26.6% and 28.4% identity to the previously characterized GDSL-like enzymes phospholipase, plant lipase, acetylcholinesterase and acetylxylan esterase, from the carbohydrate esterase family 16, respectively. Therefore, the enzyme was purified from the culture supernatant and the catalytic properties and the substrate specificity of the enzyme were investigated using different assays to reveal its potential function. While no phospholipase, acetylcholinesterase and acetylxylan esterase activities were detected, studies on the hydrolysis of ferulic acid methyl ester (~ 8.3%) and feruloylated carbohydrate 5-O-transferuloyl-arabino-furanose (~ 0.8%) showed low conversions of these substrates. By investigating the hydrolytic activity towards p-nitrophenyl-(pNP)-esters with various chain-lengths, the highest activity was determined for medium chain-length pNP-octanoate at 65 °C and a pH value of 8, while almost no activity was detected for pNP-hexanoate. The enzyme is highly stable when stored at pH 10 and 4 °C for at least 7 days. Moreover, using consensus sequence analysis and homology modeling, we could demonstrate that the PSA_Lip does not contain the usual SGNH residues in the actives site, which are usually present in GDS(L)-like enzymes.

Immobilization of Bio-imprinted Phospholipase D and Its Catalytic Behavior for Transphosphatidylation in the Biphasic System

Phospholipase D (PLD) with the higher transphosphatidylation activity was screened from Streptomyces sp. LD0501 basing on the protoplast mutagenesis technology. Then, it was successfully bio-imprinted to form a hyperactivated structure and rigidified by the intramolecular cross-linking, which was immobilized on the nonporous nanoscale silica. Characterization techniques were employed to investigate the structure and physicochemical properties of the catalysts, including Fourier transform infrared (FTIR) spectra and scanning electron microscopy (SEM) analysis. Transphosphatidylation activity and selectivity were improved significantly when immobilized PLD was used. The maximum yield for the production of phosphatidylserine (PS) reached 97% and the side reaction, the hydrolysis, was minimized. These results were further confirmed by the nuclear magnetic resonance (NMR) and mass spectrometry (MS) analysis. The imprint-induced characteristics of PLD was successfully "remembered" even in the present of much water. In addition, this immobilized hyperactivated PLD showed the excellent operational stabilities and environmental tolerances.

MIF-like domain containing protein orchestrates cellular differentiation and virulence in the fungal pathogen Magnaporthe oryzae

Macrophage migration inhibitory factor (MIF) is a pleiotropic protein with chemotactic, pro-inflammatory, and growth-promoting activities first discovered in mammals. In parasites, MIF homologs are involved in immune evasion and pathogenesis. Here, we present the first comprehensive analysis of an MIF protein from the devastating plant pathogen Magnaporthe oryzae (Mo). The fungal genome encodes a single MIF protein (MoMIF1) that, unlike the human homolog, harbors multiple low-complexity regions (LCRs) and is unique to Ascomycota. Following infection, MoMIF1 is expressed in the biotrophic phase of the fungus, and is strongly down-regulated during subsequent necrotrophic growth in leaves and roots. We show that MoMIF1 is secreted during plant infection, affects the production of the mycotoxin tenuazonic acid and inhibits plant cell death. Our results suggest that MoMIF1 is a novel key regulator of fungal virulence that maintains the balance between biotrophy and necrotrophy during the different phases of fungal infection.

Altering the Chain Length Specificity of a Lipase from Pleurotus citrinopileatus for the Application in Cheese Making

In traditional cheese making, pregastric lipolytic enzymes of animal origin are used for the acceleration of ripening and the formation of spicy flavor compounds. Especially for cheese specialities, such as Pecorino, Provolone, or Feta, pregastric esterases (PGE) play an important role. A lipase from Pleurotus citrinopileatus could serve as a substitute for these animal-derived enzymes, thus offering vegetarian, kosher, and halal alternatives. However, the hydrolytic activity of this enzyme towards long-chain fatty acids is slightly too high, which may lead to off-flavors during long-term ripening. Therefore, an optimization via protein engineering (PE) was performed by changing the specificity towards medium-chain fatty acids. With a semi-rational design, possible mutants at eight different positions were created and analyzed in silico. Heterologous expression was performed for 24 predicted mutants, of which 18 caused a change in the hydrolysis profile. Three mutants (F91L, L302G, and L305A) were used in application tests to produce Feta-type brine cheese. The sensory analyses showed promising results for cheeses prepared with the L305A mutant, and SPME-GC-MS analysis of volatile free fatty acids supported these findings. Therefore, altering the chain length specificity via PE becomes a powerful tool for the replacement of PGEs in cheese making.