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An efficient endogenous type I-E CRISPR-Cas genome-editing platform for producing transglutaminase in Streptomyces mobaraensis.

Streptomyces mobaraensis is an industrially important actinomycete capable of producing transglutaminase (TGase), a valuable crosslinking enzyme that is widely used in the food, pharmaceutical, and textile industries. However, its genetic manipulation remains challenging owing to the lack of efficient genome-editing tools. Here, we characterized an endogenous type I-E CRISPR-Cas system in S. mobaraensis IPIO2 through bioinformatics analysis and plasmid interference assays, identifying the protospacer adjacent motif as 5'-AAC-3'. We engineered an artificial editing plasmid, pCRISPR, by inserting a mini-CRISPR array (repeat-spacer-repeat) and homologous recombination repair templates into the replicative plasmid pJTU1278. This system exhibited high editing efficiencies, achieving 70% for single-gene deletions and 75-80% for large DNA fragment deletions ranging from 10 to 40 kb. Based on this system, deletion of four genes consistently downregulated during TGase production, identified through comparative proteomics, enhanced TGase production by 8.5-18.5%. Furthermore, deleting the pseudouridimycin and piericidin A1 biosynthetic gene clusters using this system significantly improved the safety profile of TGase production, resulting in a 17% increase in TGase yield. This study established a robust and efficient endogenous CRISPR-Cas-based genome-editing platform in S. mobaraensis, providing a powerful tool for strain engineering and industrial optimization of TGase production.

Comparative proteomics↗

High level expression of Streptomyces mobaraensis transglutaminase in Corynebacterium glutamicum using a chimeric pro-region from Streptomyces cinnamoneus transglutaminase.

We previously observed secretion of native-type Streptomyces mobaraensis transglutaminase (MTGase) in Corynebacterium glutamicum by co-expressing the subtilisin-like protease SAM-P45 from S. albogriseolus which processes the pro-region. In the present study, we have used a chimeric pro-region consisting of S. mobaraensis and Streptomyces cinnamoneus transglutaminases for the production of MTGase in C. glutamicum. As a result, secretion of MTGase using the chimeric pro-region is increased compared to that using the native pro-region.

Amino Acid Sequence↗

Transglutaminase from Streptomyces mobaraensis is activated by an endogenous metalloprotease.

Streptomyces mobaraensis secretes a Ca2+-independent transglutaminase (TGase) that is activated by removing an N-terminal peptide from a precursor protein during submerged culture in a complex medium [Pasternack, R., Dorsch, S., Otterbach, J. T., Robenek, I. R., Wolf, S. & Fuchsbauer, H.-L. (1998) Eur. J. Biochem. 257, 570-576]. However, an activating protease could not be identified, probably because of the presence of a 14-kDa protein (P14) belonging to the Streptomyces subtilisin inhibitor family. In contrast, if the microorganism was allowed to grow on a minimal medium, several soluble proteases were extracted, among them the TGase-activating protease (TAMEP). TAMEP was purified by sequential chromatography on DEAE- and Arg-Sepharose and used to determine the cleavage site of TGase. It was clearly shown that the peptide bond between Phe(-4) and Ser(-5) was hydrolyzed, indicating that at least one additional peptidase is necessary to complete TGase processing, even if TAMEP cleavage was sufficient to obtain total activity. Sequence analysis from the N-terminus of TAMEP revealed the close relationship to a zinc endo-protease from S. griseus. The S. griseus protease differs from other members of the M4 protease family, such as thermolysin, in that it may be inhibited by the Streptomyces subtilisin inhibitor. P14 likewise inhibits TAMEP in approximately equimolar concentrations, suggesting its important role in regulating TGase activity.

Amino Acid Sequence↗

Purification and characterization of a novel aminoacylase from Streptomyces mobaraensis.

A novel aminoacylase was purified to homogeneity from culture broth of Streptomyces mobaraensis, as evidenced by SDS-polyacrylamide gel electrophoresis (PAGE). The enzyme was a monomer with an approximate molecular mass of 100 kDa. The purified enzyme was inhibited by the presence of 1,10-phenanthroline and activated by the addition of Co2+. It was stable at temperatures of up to 60 degrees C for 1 h at pH 7.2. It showed broad substrate specificity to N-acetylated L-amino acids. It catalyzed the hydrolysis of the amide bonds of various N-acetylated L-amino acids, except for Nepsilon-acetyl-L-lysine and N-acetyl-L-proline. Hydrolysis of N-acetyl-L-methionine and N-acetyl-L-histidine followed Michaelis-Menten kinetics with K(m) values of 1.3+/-0.1 mM and 2.7+/-0.1 mM respectively. The enzyme also catalyzed the deacetylation of 7-aminocephalosporanic acid (7-ACA) and cephalosporin C. Moreover, feruloylamino acids and L-lysine derivatives of ferulic acid derivatives were synthesized in an aqueous buffer using the enzyme.

Amidohydrolases↗

Activated transglutaminase from Streptomyces mobaraensis is processed by a tripeptidyl aminopeptidase in the final step.

Transglutaminase (TGase) from Streptomyces mobaraensis is secreted as a precursor protein which is completely activated by the endoprotease TAMEP, a member of the M4 protease family [Zotzel, J., Keller, P. & Fuchsbauer, H.-L. (2003) Eur. J. Biochem. 270, 3214-3222]. In contrast with the mature enzyme, TAMEP-activated TGase exhibits an additional N-terminal tetrapeptide (Phe-Arg-Ala-Pro) suggesting truncation, at least, by a second protease. We have now isolated from the culture broth of submerged colonies a tripeptidyl aminopeptidase (SM-TAP) that is able to remove the remaining tetrapeptide. The 53-kDa peptidase was purified by ion-exchange and phenyl-Sepharose chromatography and subsequently characterized. Its proteolytic activity was highest against chromophoric tripeptides at pH 7 in the presence of 2 mm CaCl2. EDTA and EGTA (10 mm) both diminished the proteolytic activity by half. Complete inhibition was only achieved with 1 mm phenylmethanesulfonyl fluoride, suggesting that SM-TAP is a serine protease. Alignment of the N-terminal sequence confirmed its close relation to the Streptomyces TAPs. That removal of Phe-Arg-Ala-Pro from TAMEP-activated TGase by SM-TAP occurs in a single step was confirmed by experiments using various TGase fragments and synthetic peptides. SM-TAP was also capable of generating the mature N-terminus by cleavage of RAP-TGase. However, AP-TGase remained unchanged. As SM-TAP activity against chromophoric amino acids such as Pro-pNA or Phe-pNA could not be detected, the tetrapeptide of TAMEP-activated TGase must be removed without formation of an intermediate.

Amino Acid Sequence↗

Novel prolyl tri/tetra-peptidyl aminopeptidase from Streptomyces mobaraensis: substrate specificity and enzyme gene cloning.

The prolyl peptidase that removes the tetra-peptide of pro-transglutaminase was purified from Streptomyces mobaraensis mycelia. The substrate specificity of the enzyme using synthetic peptide substrates showed proline-specific activity with not only tripeptidyl peptidase activity, but also tetrapeptidyl peptidase activity. However, the enzyme had no other exo- and endo-activities. This substrate specificity is different from proline specific peptidases so far reported. The enzyme gene was cloned, based on the direct N-terminal amino acid sequence of the purified enzyme, and the entire nucleotide sequence of the coding region was determined. The deduced amino acid sequence revealed an N-terminal signal peptide sequence (33 amino acids) followed by the mature protein comprising 444 amino acid residues. This enzyme shows no remarkable homology with enzymes belonging to the prolyl oligopeptidase family, but has about 65% identity with three tripeptidyl peptidases from Streptomyces lividans, Streptomyces coelicolor, and Streptomyces avermitilis. Based on its substrate specificity, a new name, "prolyl tri/tetra-peptidyl aminopeptidase," is proposed for the enzyme.

Amino Acid Sequence↗

The pro-peptide of Streptomyces mobaraensis transglutaminase functions in cis and in trans to mediate efficient secretion of active enzyme from methylotrophic yeasts.

Transglutaminase (TGase) from the actinomycete Streptomyces mobaraensis is a useful enzyme in the food industry, and development of an efficient production system for it would be desirable. Herein we report secretion of TGase in an enzymatically active form by methylotrophic yeasts as expression hosts. Secretory production of active TGase required a pro-peptide from TGase. When an artificial Kex2-endopeptidase recognition site was placed between the pro-peptide and mature TGase, secretion and in vitro maturation of TGase depended on Kex2-dependent cleavage. Unexpectedly, coexpression of unlinked pro-peptide with mature TGase yielded efficient secretion of the active enzyme. These results indicate that the pro-peptide from TGase functions not only in an intramolecular but also in an intermolecular manner. Site-directed mutagenesis of putative N-glycosylation sites increased the productivity of the active TGase further. A recombinant Candida boidinii strain was found to secrete active TGase up to 1.83 U/ml (about 90 mg/l) after 119 h of cultivation.

Candida↗

S-peptide as a potent peptidyl linker for protein cross-linking by microbial transglutaminase from Streptomyces mobaraensis.

We have found that ribonuclease S-peptide can work as a novel peptidyl substrate in protein cross-linking reactions catalyzed by microbial transglutaminase (MTG) from Streptomyces mobaraensis. Enhanced green fluorescent protein tethered to S-peptide at its N-terminus (S-tag-EGFP) appeared to be efficiently cross-linked by MTG. As wild-type EGFP was not susceptible to cross-linking, the S-peptide moiety is likely to be responsible for the cross-linking. A site-directed mutation study assigned Gln15 in the S-peptide sequence as the sole acyl donor. Mass spectrometric analysis showed that two Lys residues (Lys5 and Lys11) in the S-peptide sequence functioned as acyl acceptors. We also succeeded in direct monitoring of the cross-linking process by virtue of fluorescence resonance energy transfer (FRET) between S-tag-EGFP and its blue fluorescent color variant (S-tag-EBFP). The protein cross-linking was tunable by either engineering S-peptide sequence or capping the S-peptide moiety with S-protein, the partner protein of S-peptide for the formation of ribonuclease A. The latter indicates that S-protein can be used as a specific inhibitor of S-peptide-directed protein cross-linking by MTG. The controllable protein cross-linking of S-peptide as a potent substrate of MTG will shed new light on biomolecule conjugation.

Amino Acid Sequence↗

A novel acylase from Streptomyces mobaraensis that efficiently catalyzes hydrolysis/synthesis of capsaicins as well as N-acyl-L-amino acids and N-acyl-peptides.

A novel enzyme that catalyzes efficient hydrolysis of capsaicin (8-methyl-N-vanillyl-6-nonenamide) was isolated from the culture broth of Streptomyces mobaraensis. The enzyme consisted of two dissimilar subunits with molecular masses of 61 and 19 kDa. The enzyme was activated and stabilized in the presence of Co2+. It showed a pH optimum of about 8 and was stable at temperatures of up to 55 degrees C for 1 h at pH 7.8. The specific activity of the enzyme for the hydrolysis of capsaicin was 10(2)-10(4) times higher than those for the enzymes reported to date. In an aqueous/n-hexane biphasic system, capsaicin analogues such as octanoyl, decanoyl, and lauroyl vanillylamides were synthesized from the corresponding fatty acids and vanillylamine at yields of 50% or greater. In addition, the enzyme catalyzed the deacylation of N-lauroyl-L-amino acids and N-lauroyl-L-dipeptides and the efficient synthesis of Nalpha-lauroyl-L-lysine, Nepsilon-lauroyl-L-lysine, and various N-lauroyl-peptides in aqueous solution in both the absence and the presence of glycerol.

Acylation↗

Taxonomic re-evaluation of whorl-forming Streptomyces (formerly Streptoverticillium) species by using phenotypes, DNA-DNA hybridization and sequences of gyrB, and proposal of Streptomyces luteireticuli (ex Katoh and Arai 1957) corrig., sp. nov., nom. rev.

The taxonomic status of 64 strains of whorl-forming Streptomyces (formerly Streptoverticillium) species was re-evaluated and strains were reclassified on the basis of their phenotypes, DNA-DNA hybridization data and partial sequences of gyrB, the structural gene of the B subunit of DNA gyrase. These strains, which consisted of 46 species and eight subspecies with validly published names and 13 species whose names have not been validly published [including 10 strains examined by the International Streptomyces Project (ISP)], were divided into two groups, namely typical and atypical whorl-forming Streptomyces species, based on their phenotypes and gyrB gene sequences. The typical whorl-forming species (59 strains) were divided into six major clusters of three or more species, seven minor clusters of two species and five single-member clusters, based on the threshold value of 97 % gyrB sequence similarity. Major clusters were typified by Streptomyces abikoensis, Streptomyces cinnamoneus, Streptomyces distallicus, Streptomyces griseocarneus, Streptomyces hiroshimensis and Streptomyces netropsis. Phenotypically, members of each cluster resembled each other closely except for the S. distallicus cluster, which was divided phenotypically into the S. distallicus and Streptomyces stramineus subclusters, and the S. netropsis cluster, which was divided into the S. netropsis and Streptomyces eurocidicus subclusters. Strains in each minor cluster closely resembled each other phenotypically. DNA-DNA relatedness between the representative species and others in each major cluster and/or subcluster, and between strains in the minor clusters, was >70 %, indicating that the major clusters and/or subclusters and the minor clusters each comprise a single species. It was concluded that 59 strains of typical whorl-forming Streptomyces species consisted of the following 18 species, including subjective synonym(s): S. abikoensis, Streptomyces ardus, Streptomyces blastmyceticus, S. cinnamoneus, S. eurocidicus, S. griseocarneus, S. hiroshimensis, Streptomyces lilacinus, 'Streptomyces luteoreticuli', Streptomyces luteosporeus, Streptomyces mashuensis, Streptomyces mobaraensis, Streptomyces morookaense, S. netropsis, Streptomyces orinoci, S. stramineus, Streptomyces thioluteus and Streptomyces viridiflavus.

Base Sequence↗

Substrate specificity analysis of microbial transglutaminase using proteinaceous protease inhibitors as natural model substrates.

The substrate specificity of microbial transglutaminase (MTG) from Streptomyces mobaraensis (formerly categorized Streptoverticillium) was studied using a Streptomyces proteinaceous protease inhibitor, STI2, as a model amine-donor substrate. Chemical modification and mutational analysis to address the substrate requirements for MTG were carried out around the putative reactive site region of STI2 on the basis of the highly refined tertiary structure and the solvent accessibility index of Streptomyces subtilisin inhibitor, SSI, a homolog of STI2. The results suggest that the P1 reactive center site (position 70 of STI2) for protease subtilisin BPN' or trypsin may be the prime Lys residue that can be recognized by MTG, when succinylated beta-casein was used as a partner Gln-substrate. It is characteristic in that the same primary enzyme contact region of STI2 is shared by both enzymes, MTG and proteases. For quantitative analysis of the TG reaction, we established an ELISA-based monitoring assay system using an anti-SSI polyclonal antibody highly cross-reactive with STI2. Site-specific STI2 mutants were prepared by an Escherichia coli expression-secretion vector system and subjected to the assay system. We reached several conclusions concerning the nature of the flanking amino acid residues affecting the MTG reactivity of the substrate Lys residue: (i) site-specific mutations from Asn to Lys or Arg at position 69 preceding the amine-donor 70Lys, led to enhanced substrate reactivity; (ii) amino acid replacement at 67Ile with Ser led to higher substrate reactivity, (iii) additive effects were obtained by a combination of the positive mutations at positions 67 and 69 as described above, and (iv) Gly at position 65 might be essential for MTG reaction. Moreover, the substrate specificity of guinea pig liver tissue transglutaminase (GTG) was compared with that of MTG using STI2 and its mutants. In contrast to MTG, replacement of Gly by Asp at position 65 was the most favorable for substrate reactivity. Also, 70Lys appeared not to be a prime amine-donor site for GTG-mediated cross-linking, suggesting a difference in substrate recognition between MTG and GTG.

Amino Acid Sequence↗

Cloning and expression of a gene encoding N-glycosyltransferase (ngt) from Saccarothrix aerocolonigenes ATCC39243.

In the course of our bioconversion studies on the derivatives of an indolocarbazole, J-104303, Saccharothrix aerocolonigenes ATCC39243 was found to convert J-104303, which was added into the culture medium, to its glycosylated derivative, J-109384. In order to clone the gene having the ability to convert J-104303 to J-109384, a library of Saccharothrix aerocolonigenes ATCC39243 DNA fragments was constructed using Streptomyces lividans TK21 and pIJ702 as host strain and vector, respectively. By examining more than 5,000 transformants, one was found to convert J-104303 to J-109384. Sequence analysis of the inserted DNA fragment revealed an open reading frame with 1,245 base pairs, named ngt. The transformant containing this ngt gene was also found to introduce a D-glucose moiety into 6-N-methylarcyriaflavin C. Furthermore, when ngt was introduced into Streptomyces mobaraensis BA13793, a producer of J-104303, the resulting transformant produced J-109384 directly.

Actinomycetales↗

Inhibition of bacterial transglutaminase by its heat-treated pro-enzyme.

Transglutaminases form a unique family of cross-linking enzymes which may be interesting for pharmaceutical and technical purposes. Bacterial transglutaminase, differing from the eucaryotic counterparts in being independent from Ca2+ ions, is excreted by several Streptomyces species. Until now an endogenous factor regulating activated transglutaminase could not be detected. Here, we investigated whether an inhibitor of transglutaminase is excreted into the culture fluid of Streptomyces mobaraensis. We could demonstrate that heat-resistant inhibitory activity is produced after 24h of growth reaching a maximum after 72h. A two-step ion exchange chromatography purification procedure revealed co-elution of the heat-treated inhibitor with pro-transglutaminase. Experiments with wild-type and recombinant pro-transglutaminase confirmed that the precursor protein indeed inhibits the activity of the mature enzyme.

Culture Media↗

N-terminal glycine-specific protein conjugation catalyzed by microbial transglutaminase.

Here, we report the N-terminal glycine (Gly) residue of a target protein can be a candidate primary amine for site-specific protein conjugation catalyzed by microbial transglutaminase (MTG) from Streptomyces mobaraensis. Gly5-enhanced green fluorescent protein (EGFP) (EGFP with five additional Gly residues at its N-terminus) was cross-linked with Myc-dihydrofolate reductase (DHFR) (DHFR with the myc epitope sequence at its N-terminus) to yield DHFR-EGFP heterodimers. The reactivities of additional peptidyl linkers were investigated and the results obtained suggested that at least three additional Gly residues at the N-terminus were required to yield the EGFP-DHFR heterodimeric form. Site-directed mutagenesis analysis revealed marked preference of MTG for amino acids adjacent to the N-terminal Gly residue involved in the protein conjugation. In addition, peptide-protein conjugation was demonstrated by MTG-catalyzed N-terminal Gly-specific modification of a target protein with the myc epitope peptide.

Base Sequence↗

Properties and applications of microbial transglutaminase.

Some properties and applications of the transglutaminase (TGase) referred to as microbial TGase (MTGase), derived from a variant of Streptomyces mobaraensis (formerly classified as Streptoverticillium mobaraense), are described. MTGase cross-linked most food proteins, such as caseins, soybean globulins, gluten, actin, myosins, and egg proteins, as efficiently as mammalian TGases by forming an epsilon-(gamma-glutamyl)lysine bond. However, unlike many other TGases, MTGase is calcium-independent and has a relatively low molecular weight. Both of these properties are of advantage in industrial applications; a number of studies have illustrated the potential of MTGase in food processing and other areas. The crystal structure of MTGase has been solved. It provides basic structural information on the MTGase and accounts well for its characteristics. Moreover, an efficient method for producing extracellular MTGase has been established using Corynebacterium glutamicum. MTGase may be expected to find many uses in both food and non-food applications.

Coenzymes↗

Enzymatic labeling of a single chain variable fragment of an antibody with alkaline phosphatase by microbial transglutaminase.

Functional cross-linking of a single chain Fv fragment of anti-hen egg-white lysozyme antibody (scFv) and alkaline phosphatase (AP) was explored using microbial transglutaminase (MTG) from Streptomyces mobaraensis. A specific peptidyl linker for MTG was genetically fused to the N-terminus of each protein and the resultant proteins were obtained separately by bacterial expression. The recombinant peptide-tagged scFv and AP were site-specifically cross-linked by MTG through the extra peptidyl linkers in vitro, which mainly yielded the heterodimer (i.e., scFv-AP conjugate). The enzymatic cross-linking reaction had little influence on either the antigen-binding ability of the scFv moiety or the enzymatic activity of the AP moiety of the conjugate, allowing use within an enzyme-linked immunosorbent assay. The results obtained suggest that the enzymatic approach with MTG facilitates the posttranslational construction of functional fusion proteins.

Alkaline Phosphatase↗

Peptidyl linkers for protein heterodimerization catalyzed by microbial transglutaminase.

Specific peptidyl linkers that result in the heterodimerization of functional proteins, which is catalyzed by microbial transglutaminase from Streptomyces mobaraensis (MTG), were generated based on a ribonuclease S-peptide using site-directed mutagenesis. The peptidyl linkers designated as Lys-tag and Gln-tag were designed to possess sole reactive Lys or Gln residue that was amenable for selective Lys-Gln cross-linkage of different proteins. Green fluorescent protein variants, ECFP and EYFP, were employed as model proteins, and those Lys- and Gln-tags were fused to the N-termini of ECFP and EYFP, respectively. As a result, we succeeded in solely obtaining the ECFP-EYFP heterodimer without forming multiply cross-linked byproducts. It was found that the reactivity of peptidyl linkers varied according to the type of amino acid to be replaced. Peptidyl linkers with a basic amino acid (Arg) exhibited the highest reactivity in the cross-linking reaction, suggesting the cationic residue substrate preference of MTG. Kinetic analysis utilizing fluorescent resonance energy transfer (FRET), that is only observed upon the heterodimeric ECFP-EYFP conjugation, revealed that the amino acid replacement contributed to the acceleration of cross-linking reactions by increasing catalytic turnover (k(cat)), rather than substrate binding affinity (K(m)). Finally, using a ribonuclease S-protein, the manipulation of enzymatic protein cross-linking based on specific S-peptide:S-protein interactions was explored. Since newly designed Lys- and Gln-tags retained binding affinities to the S-protein, the heterodimerization was perfectly restrained by wrapping them with the S-protein. The results suggest the possibility of limited protein conjugation by tuning steric hindrance against the MTG. Tailoring enzymatic posttranslational modifications with either engineering peptidyl substrates or by taking specific peptide-protein interactions into consideration may facilitate the development of a new sequential protein conjugation method for the preparation of multifunctional protein.

Catalysis↗

Secretion of human epidermal growth factor by Corynebacterium glutamicum.

AIMS: To examine the secretion of human epidermal growth factor (hEGF) by Corynebacterium glutamicum. METHODS AND RESULTS: We recently showed that a novel protein-secretion system in C. glutamicum could produce Streptomyces mobaraensis transglutaminase. In the present study, the industrially important protein hEGF was secreted into the culture medium in a fully active form by C. glutamicum and accumulated at a rate of up to 156 mg l(-1) day(-1). CONCLUSIONS: These results demonstrated that the hEGF protein could be secreted in an active form by C. glutamicum. SIGNIFICANCE AND IMPACT OF THE STUDY: Our data confirmed that the pharmaceutically important human protein hEGF could be efficiently secreted in an active form by the C. glutamicum protein-expression system. Moreover, we demonstrated that this bacterium has potential as a host for the industrial-scale production of human proteins.

Blotting, Western↗