A novel metal ion-independent phospholipase A1 of Streptomyces albidoflavus isolated from Japanese soil has been purified and characterized. The enzyme consists of a 33-residue N-terminal signal secretion sequence and a 269-residue mature protein with a deduced molecular weight of 27,199. Efficient and extracellular production of the recombinant enzyme was successfully achieved using Streptomyces lividans cells and an expression vector. A large amount (25 mg protein, 14.7 kU) of recombinant enzyme with high specific activity (588 U/mg protein) was purified by simple purification steps. The maximum activity was found at pH 7.2 and 50 °C. At pH 7.2, the enzyme preferably hydrolyzed phosphatidic acid and phosphatidylserine; however, the substrate specificity was dependent on the reaction pH. The enzyme hydrolyzed lysophosphatidylcholine and not triglyceride and the p-nitrophenyl ester of fatty acids. At the reaction equilibrium, the molar ratio of released free fatty acids (sn-1:sn-2) was 63:37. The hydrolysis of phosphatidic acid at 50 °C and pH 7.2 gave apparent Vmax and kcat values of 1389 μmol min−1 mg protein−1 and 630 s−1, respectively. The apparent Km and kcat/Km values were 2.38 mM and 265 mM−1 s−1, respectively. Mutagenesis analysis showed that Ser11 is essential for the catalytic function of the enzyme and the active site may include residues Ser216 and His218.

No abstract

A novel metal ion-independent phospholipase B (PLB 684 ) from Streptomyces sp. strain NA684 was purified 264-fold from the culture supernatant with 2.85% recovery (6330 UÁmg protein À1 ). The enzyme functions as a monomer with a molecular mass of 38.9 kDa. Maximum activity was found at pH 8.4 and 50°C. The substrate specificity was in the order: phosphatidylcholine ≥ phosphatidic acid ≥ lysophosphatidylcholine > phosphatidylserine > phosphatidylinositol > phosphatidylglycerol. The enzyme did not hydrolyze phosphatidylethanolamine, tristearin and dipalmitin. PLB 684 hydrolyzed lysophosphatidylcholine and diacylphosphatidylcholine, and lysophosphatidylcholine was primarily produced during the early stages of phosphatidylcholine hydrolysis. The apparent K m , V max and k cat for hydrolysis of dimyristoyl phosphatidic acid were 14.5 mM, 15.8 mmolÁmin À1 Ámg protein À1 and 1.02 9 10 4 s À1 , respectively. The positional specificity of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine hydrolysis was investigated using GC. In the reaction equilibrium, the molar ratio of released fatty acids (sn-1 : sn-2) was 45 : 55. The ORF of the gene is 1239 bp in length and codes for a 30-amino acid signal peptide and a 382-amino acid mature enzyme. The deduced amino acid sequence of PLB 684 shows 60% identity to a uncharacterized protein of Streptomyces auratus AGR0001 (UniProt accession number: J1RQY0). The extracellular production of PLB 684 was achieved using a pUC702 expression vector and Streptomyces lividans as the host. Mutagenesis analysis showed that Ser12 is essential for the catalytic function of PLB 684 and that the active site may include residues Ser330 and His332.

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 Km and kcat 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 http://www.chem.qmul.ac.uk/iubmb/enzyme/EC3/1/4/4.html

The substrate recognition mechanism of phospholipase D and enzymatic measurement of choline plasmalogen were investigated. A phospholipase D (PLD684) from Streptomyces sp. strain NA684 was purified 184-fold from the culture supernatant with 23.7% recovery. Maximum activity for l-α-lysophosphatidylcholine (LPC) hydrolysis was found at pH 5.0 and 80°C. The hydrolytic activity was remarkably affected by the concentration of Triton X-100 in the reaction mixture. In the presence of 0.05-0.5% and 0.1-0.2% (wt/vol) Triton X-100, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and choline plasmalogen were efficiently hydrolyzed by PLD684, respectively. Hydrolysis of LPC and choline lysoplasmalogen did not require Triton X-100; rather, the hydrolytic activity was inhibited by more than 0.05% (wt/vol) Triton X-100. The enzyme preferred mixed micelle substrates to liposomal substrates and hydrolyzed 98.4% of mixed micelle POPC in 1 h. Kinetic analysis showed that the rate-limiting steps of hydrolysis of mixed micelle POPC and emulsified LPC by PLD684 were the bulk step and the surface step, respectively. These results suggest that PLD684 has at least two substrate recognition mechanisms to recognize various phospholipids that have considerably different physical properties derived from their head and tail groups. Understanding of how PLD684 recognizes substrate forms will be useful for elucidating roles of lipolytic proteins in nature. Moreover, we report an enzymatic measurement of choline plasmalogen using PLD684 and phospholipase B. This is the first enzymatic method for measuring choline plasmalogen.