Purification, characterization, cloning and sequencing of phospholipase D from Streptomyces septatus TH-2

Efficient secretory expression of phospholipase D for the high-yield production of phosphatidylserine and phospholipid derivates from soybean lecithin

Phospholipase D (PLD) is an essential biocatalyst for the biological production of phosphatidylserine and phospholipid modification. However, the efficient heterologous expression of PLD is limited by its cell toxicity. In this study, a PLD was secretory expressed efficiently in Bacillus subtilis with an activity around 100 U/mL. A secretory expression system containing the signal peptide SP_EstA and the dual-promoter P_HpaII-SrfA was established, and the extracellular PLD activity further reached 119.22 U/mL through scale-up fermentation, 191.30-fold higher than that of the control. Under optimum reaction conditions, a 61.61% conversion ratio and 21.07 g/L of phosphatidylserine production were achieved. Finally, the synthesis system of PL derivates was established, which could efficiently synthesis novel PL derivates. The results highlight that the secretory expression system constructed in this study provides a promising PLD producing strain in industrial application, and laid the foundation for the biosynthesis of phosphatidylserine and other PL derivates. As far as we know, this work reports the highest level of extracellular PLD expression to date and the enzymatic production of several PL derivates for the first time.

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.

Phospholipids (PLs) know-how: exploring and exploiting phospholipase D for its industrial dissemination

Owing to their numerous nutritional and bioactive functions, phospholipids (PLs), which are major components of biological membranes in all living organisms, have been widely applied as nutraceuticals, food supplements, and cosmetic ingredients. To date, PLs are extracted solely from soybean or egg yolk, despite the diverse market demands and high cost, owing to a tedious and inefficient manufacturing process. A microbial-based manufacturing process, specifically phospholipase D (PLD)-based biocatalysis and biotransformation process for PLs, has the potential to address several challenges associated with the soybean- or egg yolk-based supply chain. However, poor enzyme properties and inefficient microbial expression systems for PLD limit their wide industrial dissemination. Therefore, sourcing new enzyme variants with improved properties and developing advanced PLD expression systems are important. In the present review, we systematically summarize recent achievements and trends in the discovery, their structural properties, catalytic mechanisms, expression strategies for enhancing PLD production, and its multiple applications in the context of PLs. This review is expected to assist researchers to understand current advances in this field and provide insights for further molecular engineering efforts toward PLD-mediated bioprocessing.

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.

Efficient secretion expression of phospholipase D in Bacillus subtilis and its application in synthesis of phosphatidylserine by enzyme immobilization

Transphosphatidylation catalyzed by phospholipase D has gained increasing attention for producing phosphatidylserine (PS), which can be used in functional food and medicine. In this study, we investigated the effects of six signal peptides on the secretion of PLD (PLD_sa) from Streptomyces antibioticus TCCC 21059 in the food-grade GRAS bacterium Bacillus subtilis. It indicated that the optimal signal peptide DacB with an Ala-X-Ala sequence motif at the C-terminus showed the highest secretory expression ability, resulting in increased production of 2.84 U/mL PLD_sa. Then PLD_sa was immobilized on the epoxy-based carriers, and one of these carriers allowed PLD_sa loading of up to 2.7 mg/g. The immobilized PLD_sa was more stable over a wide range of pH value (4.5-7.5) and temperature (16 °C-60 °C) than free PLD_sa. Subsequently, the synthesis of PS from soybean phosphatidylcholine (PC) was carried out in purely aqueous solution using immobilized PLD_sa, leading to a high yield of 65%. The immobilized PLD_sa catalyst maintained a relative PS production of 60% after 5 recycles. Notably, the use of toxic solvent was completely eliminated in the whole process, which would be more profitable for the application of PS.

Enhancing the thermostability of phospholipase D from Streptomyces halstedii by directed evolution and elucidating the mechanism of a key amino acid residue using molecular dynamics simulation

To enhance the thermostability of phospholipase D (PLD), error-prone polymerase chain reaction method was used to create mutants of PLD (PLD_sh) from Streptomyces halstedii. One desirable mutant (S163F) with Ser to Phe substitution at position 163 was screened with high-throughput assay. S163F exhibited a 10 °C higher optimum temperature than wild-type (WT). Although WT exhibited almost no activity after incubating at 50 °C for 40 min, S163F still displayed 27% of its highest activity after incubating at 50 °C for 60 min. Furthermore, the half-life of S163F at 50 °C was 3.04-fold higher than that of WT. The analysis of molecular dynamics simulation suggested that the Ser163Phe mutation led to the formation of salt bridge between Lys300 and Glu314 and a stronger hydrophobic interaction of Phe163 with Pro341, Leu342, and Trp460, resulting in an increased structural rigidity and overall enhanced stability at high temperature. This study provides novel insights on PLD tolerance to high temperature by investigating the structure-activity relationship. In addition, it provides strong theoretical foundation and preliminary information on the engineering of PLD with improved characteristics to meet industrial demand.

Comparison of the expression of phospholipase D from Streptomyces halstedii in different hosts and its over-expression in Streptomyces lividans

Phospholipase D (PLD) proteins from Streptomyces species are useful biocatalysts for synthesizing phospholipid derivatives relevant for the pharmaceutical and food industry from low-cost phosphatidylcholine. The overexpression of PLD in a recombinant strain is necessary to achieve large-scale PLD production. In this study, we investigated the feasibility of expressing PLD from Streptomyces halstedii in different hosts. The enzymatic activity of PLD reached 69.12 U/mL in the homologous Streptomyces lividans host, which was around 50-fold higher than that in the original host. Meanwhile, in Escherichia coli and Pichia pastoris, PLD expression was poor and showed obvious toxicity to cells, which may have been one of the reasons for low levels of PLD observed in heterologous hosts. An induced (Ptip)/constitutive (PermE*) dual-promoter expression system in S. lividans was constructed, which could achieve constitutive expression with PLD enzymatic activity of 13.41 U/mL under non-induced conditions and yield the highest PLD enzymatic activity of 68.33 U/mL with 2 μg/mL thiostreptone. The concentration of the expensive inducer was significantly reduced to only 10% of that used in the original expression system without affecting the protein expression level, which provided a good foundation for subsequent industrial applications to reduce production costs.

Loop of Streptomyces Feruloyl Esterase Plays an Important Role in the Enzyme's Catalyzing the Release of Ferulic Acid from Biomass

Feruloyl esterases (FAEs) are key enzymes required for the production of ferulic acid from agricultural biomass. Previously, we identified and characterized R18, an FAE from Streptomyces cinnamoneus NBRC 12852, which showed no sequence similarity to the known FAEs. To determine the region involved in its catalytic activity, we constructed chimeric enzymes using R18 and its homolog (TH2-18) from S. cinnamoneus strain TH-2. Although R18 and TH2-18 showed 74% identity in their primary sequences, the recombinant proteins of these two FAEs (recombinant R18 [rR18] and rTH2-18) showed very different specific activities toward ethyl ferulate. By comparing the catalytic activities of the chimeras, a domain comprised of residues 140 to 154 was found to be crucial for the catalytic activity of R18. Furthermore, we analyzed the crystal structure of rR18 at a resolution of 1.5 Å to elucidate the relationship between its activity and its structure. rR18 possessed a typical catalytic triad, consisting of Ser-191, Asp-214, and His-268, which was characteristic of the serine esterase family. By structural analysis, the above-described domain was found to be present in a loop-like structure (the R18 loop), which possessed a disulfide bond conserved in the genus Streptomyces Moreover, compared to rTH2-18 of its parental strain, the TH2-18 mutant, in which Pro and Gly residues were inserted into the domain responsible for forming the R18 loop, showed markedly high k_cat values using artificial substrates. We also showed that the FAE activity of TH2-18 toward corn bran, a natural substrate, was improved by the insertion of the Gly and Pro residues.IMPORTANCEStreptomyces species are widely distributed bacteria that are predominantly present in soil and function as decomposers in natural environments. They produce various enzymes, such as carbohydrate hydrolases, esterases, and peptidases, which decompose agricultural biomass. In this study, based on the genetic information on two Streptomyces cinnamoneus strains, we identified novel feruloyl esterases (FAEs) capable of producing ferulic acid from biomass. These two FAEs shared high similarity in their amino acid sequences but did not resemblance any known FAEs. By comparing chimeric proteins and performing crystal structure analysis, we confirmed that a flexible loop was important for the catalytic activity of Streptomyces FAEs. Furthermore, we determined that the catalytic activity of one FAE was improved drastically by inserting only 2 amino acids into its loop-forming domain. Thus, differences in the amino acid sequence of the loop resulted in different catalytic activities. In conclusion, our findings provide a foundation for the development of novel enzymes for industrial use.

High-Yield and Sustainable Production of Phosphatidylserine in Purely Aqueous Solutions via Adsorption of Phosphatidylcholine on Triton-X-100-Modified Silica

Triton X-100 was covalently bound to a surface of silica and acted as an anchor molecule to facilitate the adsorption of phosphatidylcholine (PC) in a purely aqueous solution. The silica-adsorbed PC obtained was successfully used for phospholipase D (PLD)-mediated transphosphatidylation in the production of phosphatidylserine (PS). Organic solvents were completely avoided in the whole production process. The PC loading and PS yield reached 98.9 and 99.0%, respectively. Two adsorption models were studied, and the relevant parameters were calculated to help us understand the adsorption and reaction processes deeply. In addition, the silica-adsorbed PC provides a promising way to continuously biosynthesize PS. A packed-bed reactor was employed to demonstrate the process flow of the continuous production of PS. The recyclability and stability of the Triton-X-100-modified silica were excellent, as demonstrated by its use 30 times during continuous operation without any loss of the productivity.

Mining of a phospholipase D and its application in enzymatic preparation of phosphatidylserine

Phosphatidylserine (PS) is useful as the additive in industries for memory improvement, mood enhancement and drug delivery. Conventionally, PS was extracted from soybeans, vegetable oils, egg yolk, and biomass; however, their low availability and high extraction cost were limiting factors. Phospholipase D (PLD) is a promising tool for enzymatic synthesis of PS due to its transphosphatidylation activity. In this contribution, a new and uncharacterized PLD was first obtained from GenBank database via genome mining strategy. The open reading frame consisted of 1614 bp and potentially encoded a protein of 538-amino-acid with a theoretical molecular mass of 60 kDa. The gene was successfully cloned and expressed in Escherichia coli. Its enzymatic properties were experimentally characterized. The temperature and pH optima of PLD were determined to be 60°C and 7.5, respectively. Its hydrolytic activity was improved by addition of Ca²⁺ at 5 mM as compared with the control. The enzyme displayed suitable transphosphatidylation activity and PS could be synthesized with L-serine and soybean lecithin as substrates under the catalysis of PLD. This PLD enzyme might be a potential candidate for industrial applications in PS production. To the best of our knowledge, this is the first report on genome mining of PLDs from GenBank database.

Aqueous-Solid System for Highly Efficient and Environmentally Friendly Transphosphatidylation Catalyzed by Phospholipase D To Produce Phosphatidylserine

The purely aqueous system of phospholipase D (PLD)-mediated transphosphatidylation using pre-existing carriers for the adsorption of phosphatidylcholine (PC) to act as an "artificial interface" was introduced to replace the liquid-liquid system. Toxic organic solvents are avoided during the reaction, and the free enzyme can be simply reused by centrifugation. Special attention has been paid to the effect of the pore diameter and surface area of silica gel 60H covered with PC molecules on the yield of phosphatidylserine (PS). Results indicated that the highest PS yield of 99.5% was achieved. Moreover, 73.6% of the yield of PS was obtained after being used for six batches. This is the first description of the remarkably high reusability of free enzymes for enzymatic synthesis of PS as well. The excellent results make the aqueous-solid system more promising candidates for the industrial production of PS.

High-yield phosphatidylserine production via yeast surface display of phospholipase D from Streptomyces chromofuscus on Pichia pastoris

The gene encoding phospholipase D (PLD) from Streptomyces chromofuscus was displayed on the cell surface of Pichia pastoris GS115/pKFS-pldh using a Flo1p anchor attachment signal sequence (FS anchor). The displayed PLD (dPLD) showed maximum enzymatic activity at pH 6.0 and 55 °C and was stable within a broad range of temperatures (20-65 °C) and pHs (pH 4.0-11.0). In addition, the thermostability, acid stability and organic solvent tolerance of the dPLD were significantly enhanced compared with the secreted PLD (sPLD) from S. chromofuscus. Use of dPLD for conversion of phosphatidylcholine (PC) and l-serine to phosphatidylserine (PS) showed that 67.5% of PC was converted into PS at the optimum conditions. Moreover, the conversion rate of PS remained above 50% after 7 repeated batch cycles. Thus, P. pastoris GS115/pKFS-pldh shows the potential for viable industrial production of PS.

Phospholipase D as a catalyst: application in phospholipid synthesis, molecular structure and protein engineering

Phospholipase D (PLD) is a useful enzyme for its transphosphatidylation activity, which enables the enzymatic synthesis of various phospholipids (PLs). Many reports exist on PLD-mediated synthesis of natural and tailor-made PLs with functional head groups, from easily available lecithin or phosphatidylcholine. Early studies on PLD-mediated synthesis mainly employed enzymes of plant origin, which were later supplanted by ones from microorganisms, especially actinomycetes. Many PLDs are members of the PLD superfamily, having one or two copies of a signature sequence, HxKxxxxD or HKD motif, in the primary structures. PLD superfamily members share a common core structure, and thereby, a common catalytic mechanism. The catalysis proceeds via two-step reaction with the formation of phosphatidyl-enzyme intermediate. Both of the two catalytic His residues are critical in the reaction course, where one acts as a nucleophile, while the other functions as a general acid/base. PLD is being engineered to improve its activity and stability, alter head group specificity and further identify catalytically important residues. Since the knowledge on PLD enzymology is constantly expanding, this review focuses on recent advances in the field, regarding PLD-catalyzed synthesis of bioactive PLs, deeper understanding of substrate recognition and binding mechanism, altering substrate specificity, and improving thermostability. We introduced some of our recent results in combination with existing facts to further deepen the story on the nature of this useful enzyme.

Large-scale production of phospholipase D from Streptomyces racemochromogenes and its application to soybean lecithin modification

Phospholipase D (PLD) catalyzes transphosphatidylation, causing inter-conversion of the polar head group of phospholipids and phospholipid hydrolysis. Previously, we cloned PLD103, a PLD with high transphosphatidylation activity, from Streptomyces racemochromogenes strain 10-3. Here, we report the construction of an expression system for the PLD103 gene using Streptomyces lividans as the host bacterium to achieve large-scale production. The phosphatidylcholine (PC) hydrolysis activity of S. lividans transformed with the expression plasmid containing the PLD103 gene was approximately 90-fold higher than that of the original strain. The recombinant PLD103 (rPLD103) found in the supernatant of the transformant culture medium was close to homogeneous. The rPLD103 was indistinguishable from the native enzyme in molecular mass and enzymatic properties. Additionally, rPLD103 had high transphosphatidylation activity on PC as a substrate in a simple aqueous one-phase reaction system and was able to modify the phospholipid content of soybean lecithin. Consequently, the expression system produces a stable supply of PLD, which can then be used in the production of phosphatidyl derivatives from lecithin.

Recent progress on phospholipases: different sources, assay methods, industrial potential and pathogenicity

Significant studies on phospholipases optimization, characterization, physiological role and industrial potential have been conducted worldwide. Some of them have been directed for biotechnological advances such as gene discovery and functional enhancement by protein engineering. Others reported phospholipases as virulence factor and major cause of pathophysiological effects. A general overview on phospholipase is needed for the identification of new reliable and efficient phospholipase, which would be potentially used in number of industrial and medical applications. Phospholipases catalyse the hydrolysis of one or more ester and phosphodiester bonds of glycerophospholipids. They vary in site of action on phospholipid which can be used industrially for modification/production of new phospholipids. Catalytically active phospholipase mainly use phosphatidylcholine as major substrate, but they can also show specificity with other phospholipids. Several accurate phospholipase assay methods are known, but a rapid and reliable method for high-throughput screening is still a challenge for efficient supply of superior phospholipases and their practical applications. Major application of phospholipase is in industries like oil refinery, health food manufacturing, dairy, cosmetics etc. All types of phospholipases can be involved as virulence factor. They can also be used as diagnostic markers for microbial infection. The importance of phospholipase in virulence is proven and inhibitors of the enzyme can be used as candidate for preventing the associated disease.

Phospholipase D mechanism using Streptomyces PLD

Phospholipase D (PLD) plays various roles in important biological processes and physiological functions, including cell signaling. Streptomyces PLDs show significant sequence similarity and belong to the PLD superfamily containing two catalytic HKD motifs. These PLDs have conserved catalytic regions and are among the smallest PLD enzymes. Therefore, Streptomyces PLDs are thought to be suitable models for studying the reaction mechanism among PLDs from other sources. Furthermore, Streptomyces PLDs present advantages related to their broad substrate specificity and ease of enzyme preparation. Moreover, the tertiary structure of PLD has been elucidated only for PLD from Streptomyces sp. PMF. This article presents a review of recently reported studies of the mechanism of the catalytic reaction, substrate recognition, substrate specificity and stability of Streptomyces PLD using various protein engineering methods and surface plasmon resonance analysis.

A novel low molecular weight phospholipase D from Streptomyces sp. CS684

With the aim of isolating economically viable enzymes from a microbial source, a novel phospholipase D (PLD) was purified from Streptomyces sp. CS684 (PLD(684)). PLD(684) had molecular weight of 29 kDa, which makes it the second smallest PLD reported so far. The enzyme activity was optimum at pH 6 and 45 degrees C, and enhanced by various detergents. It was stable from pH 7 to 9 and at or below 45 degrees C when assayed after 40 h and 2h, respectively. The K(m) and V(max) values for phosphatidylcholine were 1.16 mM and 1453.74 micromol min(-1)mg(-1), respectively. It catalyzed the transphosphatidylation of glycerol, but not that of l-serine, myo-inositol or ethanolamine. Low molecular weight PLD(684) with transphosphatidylation activity may be utilized in the industrial production of rare and commercially important phospholipids.

A novel alkalo- and thermostable phospholipase D from Streptomyces olivochromogenes

A 60 kDa phospholipase D (PLD) was obtained from Streptomyces olivochromogenes by one-step chromatography on Sepharose CL-6B. Maximal activity was at pH 8 and 75 degrees C and the enzyme was stable from pH 7 to 13 and from 55 to 75 degrees C. Thermal and pH stability with temperature optimum of the enzyme were highest among Streptomyces PLDs reported so far. The activity was Ca(2+)-dependent and enhanced by detergents. The Km and Vmax values for phosphatidylcholine were 0.6 mM and 650 mumol min(-1) mg(-1), respectively. In addition, the enzyme also revealed transphosphatidylation activity, which was optimum at pH 8 and 50 degrees C. The first 15 amino acid residues of the N terminal sequence were ADYTPGAPGIGDPYY, which are significantly different from the other known PLDs. The enzyme may therefore be a novel PLD with potential application in the lipid industry.

Sensor of phospholipids in Streptomyces phospholipase D

Recently, we identified Ala426 and Lys438 of phospholipase D from Streptomyces septatus TH-2 (TH-2PLD) as important residues for activity, stability and selectivity in transphosphatidylation. These residues are located in a C-terminal flexible loop separate from two catalytic HxKxxxxD motifs. To study the role of these residues in substrate recognition, we evaluated the affinities of inactive mutants, in which these residues were substituted with Phe and His, toward several phospholipids by SPR analysis. By substituting Ala426 and Lys438 with Phe and His, respectively, the inactive mutant showed a much stronger interaction with phosphatidylcholine and a weaker interaction with phosphatidylglycerol than the inactive TH-2PLD mutant. We demonstrated that Ala426 and Lys438 of TH-2PLD play a role in sensing the head group of phospholipids.

Recognition of phospholipids in Streptomyces phospholipase D

To investigate the contribution of amino acid residues to the enzyme reaction of Streptomyces phospholipase D (PLD), we constructed a chimeric gene library between two highly homologous plds, which indicated different activity in transphosphatidylation, using RIBS (repeat-length independent and broad spectrum) in vivo DNA shuffling. By comparing the activities of chimeras, six candidate residues related to transphosphatidylation activity were shown. Based on the above result, we constructed several mutants to identify the key residues involved in the recognition of phospholipids. By kinetic analysis, we identified that Gly188 and Asp191 of PLD from Streptomyces septatus TH-2, which are not present in the highly conserved catalytic HXKXXXXD (HKD) motifs, are key amino acid residues related to the transphosphatidylation activity. To investigate the role of two residues in the recognition of phospholipids, the effects of these residues on binding to substrates were analyzed by surface plasmon spectroscopy. The result suggests that Gly188 and Asp191 are involved in the recognition of phospholipids in correlation with the N-terminal HKD motif. Furthermore, this study also provides experimental evidence that the N-terminal HKD motif contains the catalytic nucleophile, which attacks the phosphatidyl group of the substrate.

Repeat-length-independent broad-spectrum shuffling, a novel method of generating a random chimera library in vivo

We describe a novel method of random chimeragenesis based on highly frequent deletion formation in the Escherichia coli ssb-3 strain and a deletion-directed chimera selection system that uses the rpsL(+) gene as a reporter. It enables the selection of chimeras without target gene expression and can therefore be applied to cytotoxic targets. When this system was applied to phospholipase D genes from Streptomyces septatus TH-2 and Streptomyces halstedii subsp. scabies K6 (examples of cytotoxic targets), chimeragenesis occurred between short identical sequences at the corresponding position of the parental genes with large variations. Chimeragenesis was >1,000 times more frequent in the ssb-3 background than in the ssb(+) background. We called this system repeat-length-independent broad-spectrum shuffling. It enables the convenient chimeragenesis and functional study of chimeric proteins. In fact, we found two amino acid residues related to the thermostability of phospholipase D (Phe426 and Thr433) by comparing thermostability among the chimeric enzymes obtained.

Purification, characterization cloning, and sequencing of metalloendopeptidase from Streptomyces septatus TH-2

Streptomyces septatus TH-2 secretes a large amount of a protease when cultured on a medium containing K(2)HPO(4) and glucose. The enzyme was purified to homogeneity by a three-step procedure. This enzyme had a molecular mass of approximately 35kDa, and was particularly inhibited by EDTA and phosphoramidon. Its substrate specificity was investigated using novel fluorescence energy transfer combinatorial libraries. The protease was found to prefer Phe and Tyr at the P(1) position, a hydrophobic or basic residue at the P(2) position, and a basic or small residue at the P(3) position. Its gene was cloned and sequenced, and its deduced amino acid sequence contained an HEXXH consensus sequence for zinc binding, confirming that it encodes metalloendopeptidase. The primary structure of the enzyme showed 40 and 69% identities with that of thermolysin from Bacillus thermoproteolyticus and that of a metalloendopeptidase from Streptomyces griseus, respectively.

Experimental and theoretical bases of specific affinity, a cytoarchitecture-based formulation of nutrient collection proposed to supercede the Michaelis-Menten paradigm of microbial kinetics

A theory for solute uptake by whole cells was derived with a focus on the ability of oligobacteria to sequester nutrients. It provided a general relationship that was used to obtain the kinetic constants for in situ marine populations in the presence of naturally occurring substrates. In situ affinities of 0.9 to 400 liters g of cells(-1) h(-1) found were up to 10(3) times smaller than those from a "Marinobacter arcticus " isolate, but springtime values were greatly increased by warming. Affinities of the isolate for usual polar substrates but not for hydrocarbons were diminished by ionophores. A kinetic curve or Monod plot was constructed from the best available data for cytoarchitectural components of the isolate by using the theory together with concepts and calculations from first principles. The order of effect of these components on specific affinity was membrane potential > cytoplasmic enzyme concentration > cytoplasmic enzyme affinity > permease concentration > area of the permease site > translation coefficient > porin concentration. Component balance was influential as well; a small increase in cytoplasmic enzyme concentration gave a large increase in the effect of permease concentration. The effect of permease concentration on specific affinity was large, while the effect on K(m) was small. These results are in contrast to the Michaelis-Menten theory as applied by Monod that has uptake kinetics dependent on the quality of the permease molecules, with K(m) as an independent measure of affinity. Calculations demonstrated that most oligobacteria in the environment must use multiple substrates simultaneously to attain sufficient energy and material for growth, a requirement consistent with communities largely comprising few species.

Asymmetric in vitro synthesis of diastereomeric phosphatidylglycerols from phosphatidylcholine and glycerol by bacterial phospholipase D

Using chiral-phase HPLC, we determined the stereochemical configuration of the phosphatidylglycerols (PtdGro) synthesized in vitro from 1,2-diacyl-sn-glycero-3-phosphocholine (PtdCho, R configuration) or 1,2-diacyl-sn-glycero-3-phosphoethanolamine (PtdEtn, R configuration) and glycerol by transphosphatidylation with bacterial phospholipase D (PLD). The results obtained with PLD preparations from three Streptomyces strains (S. septatus TH-2, S. halstedii K5, and S. halstedii subsp. scabies K6) and one Actinomadura species were compared with those obtained using cabbage and peanut PLD. The reaction was carried out at 30 degrees C in a biphasic system consisting of diethyl ether and acetate buffer. The resulting PtdGro were then converted into bis(3,5-dinitrophenylurethane) derivatives, which were separated on an (R)-1-(1-naphthyl)ethylamine polymer. In contrast to the cabbage and peanut PLD, which gave equimolar mixtures of the R,S and R,R diastereomers, as previously established, the bacterial PLD yielded diastereomixtures of 30-40% 1,2-diacyl-sn-glycero-3-phospho-1'-sn-glycerol (R,S configuration) and 60-70% 1,2-diacyl-sn-glycero-3-phospho-3'-sn-glycerol (R,R configuration). The highest disproportionation was found for the Streptomyces K6 species. The present study demonstrates that bacterial PLD-catalyzed transphosphatidylation proceeds to a considerable extent stereoselectively to produce PtdGro from PtdCho or PtdEtn and prochiral glycerol, indicating a preference for the sn-3' position of the glycerol molecule.

Gene cloning and overproduction of an aminopeptidase from Streptomyces septatus TH-2, and comparison with a calcium-activated enzyme from Streptomyces griseus

An aminopeptidase secreted from Streptomyces septatus TH-2 (SSAP) was identified as a heat stable enzyme, and the Ssap gene was cloned and sequenced. The primary structure of SSAP showed 71% identity with that of a Streptomyces griseus aminopeptidase (SGAP), however, it lacked a unique calcium binding site. The recombinant SSAP was overexpressed in the culture supernatant of Escherichia coli harboring pET-KmS2. A comparison of recombinant SSAP and SGAP showed that both enzymes are different in terms of modulation by calcium and substrate specificity. The activity of SSAP was not modulated by calcium, while SGAP is a calcium-activated enzyme. SSAP catalyzed the hydrolysis of L-Lys-pNA efficiently whereas the reaction rate for L-Lys-pNA hydrolysis of SGAP was significantly low. Furthermore, in SGAP, the presence of Ca2+ decreased the reaction rate of L-Lys-pNA hydrolysis. SSAP also had different pKas s of reaction from that of SGAP, although almost all the residues which compose the active site were conserved in both enzymes. This result indicates that SSAP has a different environment of substrate binding and active sites from those of SGAP.

A mutant phospholipase D with enhanced thermostability from Streptomyces sp

To investigate the contribution of amino acid residues to the thermostability of phospholipase D (PLD), a chimeric form of two Streptomyces PLDs (thermolabile K1PLD and thermostable TH-2PLD) was constructed. K/T/KPLD, in which residues 329-441 of K1PLD were recombined with the homologous region of TH-2PLD, showed a thermostability midway between those of K1PLD and TH-2PLD. By comparing the primary structures of Streptomyces PLDs, the seven candidates of thermostability-related amino acid residues of K1PLD were identified. The K1E346DPLD mutant, in which Glu346 of K1PLD was substituted with Asp by site-directed mutagenesis, exhibited enhanced thermostability, which was almost the same as that of TH-2PLD.

Study on thermostability of phospholipase D from Streptomyces sp

Four phospholipases D (PLDs) in the culture supernatants from Streptomyces strains were purified to conduct a comparative study of their thermostabilities. Among the four purified PLDs, the enzyme from Streptomyces halstedii K1 lost its activity at 45 degrees C. PLD from Streptomyces septatus TH-2 was stable at the same temperature. We determined the nucleotide sequence encoding the PLD gene from S. halstedii K1 (K1PLD). The deduced amino acid sequence showed high homology to that of the PLD gene from S. septatus TH-2 (TH-2PLD). By comparison of the optimum temperature and the thermostability among recombinant PLDs, K1PLD, TH-2PLD and T/KPLD that possessed the N-terminus of TH-2PLD and the C-terminus of K1PLD, T/KPLD showed the properties midway between those of K1PLD and TH-2PLD. It was suggested that the 176 amino acids at C-terminus of Streptomyces PLD were important for its thermostability.