Substrate recognition mechanism of Streptomyces phospholipase D and enzymatic measurement of plasmalogen

Novel reaction systems for catalytic synthesis of structured phospholipids

Phospholipids are distinctive, adaptable molecules that are crucial to numerous biological systems. Additionally, their various architectures and amphiphilic characteristics support their unrivaled crucial functions in scientific and industrial applications. Due to their enormous potential for use in the fields of medicine, food, cosmetics, and health, structured phospholipids, which are modified phospholipids, have garnered increased attention. Traditional extraction methods, however, are pricy, resource-intensive, and low-yielding. The process of enzyme-catalyzed conversion is effective for producing several types of structured phospholipase. However, most frequently employed catalytic procedures involve biphasic systems with organic solvents, which have a relatively large mass transfer resistance and are susceptible to solvent residues and environmental effects due to the hydrophobic nature of phospholipids. Therefore, the adoption of innovative, successful, and environmentally friendly enzyme-catalyzed conversion systems provides a new development route in the field of structured phospholipids processing. Several innovative catalytic reaction systems are discussed in this mini-review, including aqueous-solid system, mixed micelle system, water-in-oil microemulsion system, Pickering emulsion system, novel solvent system, three-liquid-phase system, and supercritical carbon dioxide solvent system. However, there is still a glaring need for a thorough examination of these systems for the enzymatic synthesis of structural phospholipids. In terms of the materials utilized, applicability, benefits and drawbacks, and comparative effectiveness of each system, this research establishes further conditions for the system's selection. To create more effective biocatalytic processes, it is still important to build green biocatalytic processes with improved performance. KEY POINTS: • The latest catalytic systems of phospholipase D are thoroughly summarized. • The various systems are contrasted, and their traits are enumerated. • Different catalytic systems' areas of applicability and limitations are discussed.

ARTP mutagenesis of phospholipase D-producing strain Streptomyces hiroshimensis SK43.001, and its enzymatic properties

Phospholipase D (PLD) is a group of enzymes that act on phospholipid molecules, which is widely used in the fields of food and medicine. PLD is extracted from animals and plants with low transesterification activity and high price. Therefore, it is benefit to screen an efficient PLD producing strain from microorganisms. A highly productive strain of PLD with transphosphatidylation activity, named Streptomyces hiroshimensis SK43.001, was screened from soil in our laboratory and mutated using atmospheric room temperature plasma (ARTP). A mutant strain SK43.001-11 with the highest enzyme activity and superior genetic stability was obtained, and its fermentation enzyme activity was 5.3 U/mL, which was 82% increased comparing to wild strain. The purification of PLD showed that the specific enzyme activity increased to 49.48 U/mg, which was 54.37-fold higher than that of the crude enzyme, with a recovery of 32.31%. In addition, enzymatic properties of PLD have revealed that the optimal pH and temperature were 7.0 and 60 °C, respectively. Metal ion Mg²⁺ and surfactant Triton X-100 made the enzymatic activity increased by 16% and 100%, respectively. The reaction kinetic parameters showed that the mutant PLD had higher affinity for the substrate of egg PC and better catalytic efficiency with K _m, V _max and K _cat of 30.20 mmol/L, 99.70 μmol/min and 76.33 s^-1, respectively. This study may provide important inspiration for obtaining high enzyme activity strains with PLD.

Characterization of a phospholipase D from Streptomyces cinnamoneum SK43.003 suitable for phosphatidylserine synthesis

A phospholipase D high producing strain with transphosphatidylation activity that is suitable for phosphatidylserine synthesis was screened by our laboratory and named as Streptomyces cinnamoneum SK43.003. The enzyme structural and biochemical properties were investigated using the molecular biology method. A 1521-bp fragment of the phospholipase D gene from Streptomyces cinnamoneum SK43.003 was amplified by PCR and encoded for 506 amino acids. The primary structure contained two conserved HKD and GG/S motifs. The pld gene was cloned and expressed in Escherichia coli. The purified enzyme exhibited the highest activity at a pH value of 6.0 andtemperature of 60°C. The enzyme was stable within a pH range of 4-7 for 24 h or at temperatures below 50°C. In addition, Triton X-100, Fe²⁺ , and Al³⁺ were beneficial to the enzyme activity, whereas Zn²⁺ and Cu²⁺ dramatically inhibited its activity. In a two-phase system, the enzyme could convert phosphatidylcholine to phosphatidylserine with a 92% transformation rate.

Reaction Specificity of Phospholipase D Prepared from Acinetobacter radioresistens a2 in Transphosphatidylation

Phospholipase D (PLD) can react with phospholipids as substrates, generally phosphatidylcholine (PtdCho), and the PLD-substrate intermediate can be cleaved by another alcohol, resulting in transphosphatidylation of the substrate, which can be used in the production of special lipids. In this study, the reaction conditions affecting the transphosphatidylation of PtdCho with serine were optimized and the reaction specificity of a novel PLD prepared from Acinetobacter radioresistens a2 was evaluated for transphosphatidylation with a variety of phospholipid substrates and head group donors. Based on the yield of phosphatidylserine, experimental kinetic data, maximum transphosphatidylation rate, and kinetic constant, the specificity of PLD in transphosphatidylation was found to be affected by unsaturated fatty-acid phospholipid substrates. The catalytic efficiency of PLD prepared from A. radioresistens a2 on the synthesis of natural phospholipids is on the order of l-serine > ethanolamine and glycerol ≫ inositol. Moreover, it was found that the transphosphatidylation of PtdCho with saccharides was related to the length of the carbon chain and the number of saccharide units.

Molecular cloning, heterologous expression, and enzymatic characterization of lysoplasmalogen-specific phospholipase D from Thermocrispum sp

Lysoplasmalogen (LyPls)‐specific phospholipase D (LyPls‐PLD) is an enzyme that catalyses the hydrolytic cleavage of the phosphoester bond of LyPls, releasing ethanolamine or choline, and 1‐(1‐alkenyl)‐sn‐glycero‐3‐phosphate (lysoplasmenic acid). Little is known about LyPls‐PLD and metabolic pathways of plasmalogen (Pls). Reportedly, Pls levels in human serum/plasma correlate with several diseases such as Alzheimer's disease and arteriosclerosis as well as a variety of biological processes including apoptosis and cell signaling. We identified a LyPls‐PLD from Thermocrispum sp. strain RD004668, and the enzyme was purified, characterized, cloned, and expressed using pET24a(+)/Escherichia coli with a His tag. The enzyme's preferred substrate was choline LyPls (LyPlsCho), with only modest activity toward ethanolamine LyPls. Under optimum conditions (pH 8.0 and 50 °C), steady‐state kinetic analysis for LyPlsCho yielded K_m and k_cat values of 13.2 μm and 70.6 s⁻¹, respectively. The ORF of LyPls‐PLD gene consisted of 1005 bp coding a 334‐amino‐acid (aa) protein. The deduced aa sequence of LyPls‐PLD showed high similarity to those of glycerophosphodiester phosphodiesterases (GDPDs); however, the substrate specificity differed completely from those of GDPDs and general phospholipase Ds (PLDs). Structural homology modeling showed that two putative catalytic residues (His46, His88) of LyPls‐PLD were highly conserved to GDPDs. Mutational and kinetic analyses suggested that Ala55, Asn56, and Phe211 in the active site of LyPls‐PLD may participate in the substrate recognition. These findings will help to elucidate differences among LyPls‐PLD, PLD, and GDPD with regard to function, substrate recognition mechanism, and biochemical roles.

Data Accessibility

Thermocrispum sp. strain RD004668 and its 16S rDNA sequence were deposited in the NITE Patent Microorganisms Depositary (NPMD; Chiba, Japan) as NITE BP‐01628 and in the DDBJ database under the accession number AB873024. The nucleotide sequences of the 16S rDNA of strain RD004668 and the LyPls‐PLD gene were deposited in the DDBJ database under the accession numbers AB873024 and AB874601, respectively.

Enzyme

EC number EC 3.1.4.4