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Lichenysins are surface-active lipopeptides with antibiotic properties produced nonribosomally by several strains of Bacillus licheniformis. Here, we report the cloning and sequencing of an entire 26.6-kb lichenysin biosynthesis operon from B. licheniformis ATCC 10716. Three large open reading frames coding for peptide synthetases, designated licA, licB (three modules each), and licC (one module), could be detected, followed by a gene, licTE, coding for a thioesterase-like protein. The domain structure of the seven identified modules, which resembles that of the surfactin synthetases SrfA-A to -C, showed two epimerization domains attached to the third and sixth modules. The substrate specificity of the first, fifth, and seventh recombinant adenylation domains of LicA to -C (cloned and expressed in Escherichia coli) was determined to be Gln, Asp, and Ile (with minor Val and Leu substitutions), respectively. Therefore, we suppose that the identified biosynthesis operon is responsible for the production of a lichenysin variant with the primary amino acid sequence l-Gln–l-Leu–d-Leu–l-Val–l-Asp–d-Leu–l-Ile, with minor Leu and Val substitutions at the seventh position.Many strains of Bacillus are known to produce lipopeptides with remarkable surface-active properties (11). The most prominent of these powerful lipopeptides is surfactin from Bacillus subtilis (1). Surfactin is an acylated cyclic heptapeptide that reduces the surface tension of water from 72 to 27 mN m−1 even in a concentration below 0.05% and shows some antibacterial and antifungal activities (1). Some B. subtilis strains are also known to produce other, structurally related lipoheptapeptides (Table (Table1),1), like iturin (32, 34) and bacillomycin (3, 27, 30), or the lipodecapeptides fengycin (50) and plipastatin (29).
Open in a separate windowaFA, β-hydroxy fatty acid. The β-hydroxy group forms an ester bond with the carboxy group of the C-terminal amino acid. bFA, β-hydroxy fatty acid. The β-hydroxy group forms an ester bond with the carboxy group of Asp5. cFA, β-amino fatty acid. The β-amino group forms a peptide bond with the carboxy group of the C-terminal amino acid. dOnly the following combinations of amino acid 1 and 5 are allowed: Gln-Asp or Glu-Asn. eWhere an alternative amino acid may be present in a structure, the alternative is also presented. In addition to B. subtilis, several strains of Bacillus licheniformis have been described as producing the lipopeptide lichenysin (14, 17, 23, 26, 51). Lichenysins can be grouped under the general sequence l-Glx–l-Leu–d-Leu–l-Val–l-Asx–d-Leu–l-Ile/Leu/Val (Table (Table1).1). The first amino acid is connected to a β-hydroxyl fatty acid, and the carboxy-terminal amino acid forms a lactone ring to the β-OH group of the lipophilic part of the molecule. In contrast to the lipopeptide surfactin, lichenysins seem to be synthesized during growth under aerobic and anaerobic conditions (16, 51). The isolation of lichenysins from cells growing on liquid mineral salt medium on glucose or sucrose basic has been studied intensively. Antimicrobial properties and the ability to reduce the surface tension of water have also been described (14, 17, 26, 51). The structural elucidation of the compounds revealed slight differences, depending on the producer strain. Various distributions of branched and linear fatty acid moieties of diverse lengths and amino acid variations in three defined positions have been identified (Table (Table11).In contrast to the well-defined methods for isolation and structural characterization of lichenysins, little is known about the biosynthetic mechanisms of lichenysin production. The structural similarity of lichenysins and surfactin suggests that the peptide moiety is produced nonribosomally by multifunctional peptide synthetases (7, 13, 25, 49, 53). Peptide synthetases from bacterial and fungal sources describe an alternative route in peptide bond formation in addition to the ubiquitous ribosomal pathway. Here, large multienzyme complexes affect the ordered recognition, activation, and linking of amino acids by utilizing the thiotemplate mechanism (19, 24, 25). According to this model, peptide synthetases activate their substrate amino acids as aminoacyl adenylates by ATP hydrolysis. These unstable intermediates are subsequently transferred to a covalently enzyme-bound 4′-phosphopantetheinyl cofactor as thioesters. The thioesterified amino acids are then integrated into the peptide product through a stepwise elongation by a series of transpeptidations directed from the amino terminals to the carboxy terminals. Peptide synthetases have not only awakened interest because of their mechanistic features; many of the nonribosomally processed peptide products also possess important biological and medical properties.In this report we describe the identification and characterization of a putative lichenysin biosynthesis operon from B. licheniformis ATCC 10716. Cloning and sequencing of the entire lic operon (26.6 kb) revealed three genes, licA, licB, and licC, with structural patterns common to peptide synthetases and a gene designated licTE, which codes for a putative thioesterase. The modular organization of the sequenced genes resembles the requirements for the biosynthesis of the heptapeptide lichenysin. Based on the arrangement of the seven identified modules and the tested substrate specificities, we propose that the identified genes are involved in the nonribosomal synthesis of the portion of the lichenysin peptide with the primary sequence l-Gln–l-Leu–d-Leu–l-Val–l-Asp–d-Leu–l-Ile (with minor Val and Leu substitutions). 相似文献
TABLE 1
Lipoheptapeptide antibiotics of Bacillus spp.Lipopeptide | Organism | Structure | Reference |
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Lichenysin A | B. licheniformis | FAa-L-Glu-L-Leu-D-Leu-L-Val-L-Asn-D-Leu-L-Ile | 51, 52 |
Lichenysin B | FAa-L-Glu-L-Leu-D-Leu-L-Val-L-Asp-D-Leu-L-Leu | 23, 26 | |
Lichenysin C | FAa-L-Glu-L-Leu-D-Leu-L-Val-L-Asp-D-Leu-L-Ile | 17 | |
Lichenysin D | FAa-L-Gln-L-Leu-D-Leu-L-Val-L-Asp-D-Leu-L-Ile | This work | |
Surfactant 86 | B. licheniformis | FAa-L-Glxd-L-Leu-D-Leu-L-Val-L-Asxd-D-Leu-L-Ilee | 14, 15 |
L-Val | |||
Surfactin | B. subtilis | FAa-L-Glu-L-Leu-D-Leu-L-Val-L-Asp-D-Leu-L-Leu | 1, 7, 49 |
Esperin | B. subtilis | FAb-L-Glu-L-Leu-D-Leu-L-Val-L-Asp-D-Leu-L-Leue | 45 |
L-Val | |||
Iturin A | B. subtilis | FAc-L-Asn-D-Tyr-D-Asn-L-Gln-L-Pro-D-Asn-L-Ser | 32 |
Iturin C | FAc-L-Asn-D-Tyr-D-Asn-L-Gln-L-Pro-D-Asne-L-Asne | 34 | |
D-Ser-L-Thr | |||
Bacillomycin L | B. subtilis | FAc-L-Asp-D-Tyr-D-Asn-L-Ser-L-Gln-D-Proe-L-Thr | 3 |
D-Ser- | |||
Bacillomycin D | FAc-L-Asp-D-Tyr-D-Asn-L-Pro-L-Glu-D-Ser-L-Thr | 30, 31 | |
Bacillomycin F | FAc-L-Asn-D-Tyr-D-Asn-L-Gln-L-Pro-D-Asn-L-Thr | 27 |
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Rajesh Kasiviswanathan Matthew J. Longley Sherine S. L. Chan William C. Copeland 《The Journal of biological chemistry》2009,284(29):19501-19510
Forty-five different point mutations in POLG, the gene encoding the catalytic subunit of the human mitochondrial DNA polymerase (pol γ), cause the early onset mitochondrial DNA depletion disorder, Alpers syndrome. Sequence analysis of the C-terminal polymerase region of pol γ revealed a cluster of four Alpers mutations at highly conserved residues in the thumb subdomain (G848S, c.2542g→a; T851A, c.2551a→g; R852C, c.2554c→t; R853Q, c.2558g→a) and two Alpers mutations at less conserved positions in the adjacent palm subdomain (Q879H, c.2637g→t and T885S, c.2653a→t). Biochemical characterization of purified, recombinant forms of pol γ revealed that Alpers mutations in the thumb subdomain reduced polymerase activity more than 99% relative to the wild-type enzyme, whereas the palm subdomain mutations retained 50–70% wild-type polymerase activity. All six mutant enzymes retained physical and functional interaction with the pol γ accessory subunit (p55), and none of the six mutants exhibited defects in misinsertion fidelity in vitro. However, differential DNA binding by these mutants suggests a possible orientation of the DNA with respect to the polymerase during catalysis. To our knowledge this study represents the first structure-function analysis of the thumb subdomain in pol γ and examines the consequences of mitochondrial disease mutations in this region.As the only DNA polymerase found in animal cell mitochondria, DNA polymerase γ (pol γ)3 bears sole responsibility for DNA synthesis in all replication and repair transactions involving mitochondrial DNA (1, 2). Mammalian cell pol γ is a heterotrimeric complex composed of one catalytic subunit of 140 kDa (p140) and two 55-kDa accessory subunits (p55) that form a dimer (3). The catalytic subunit contains an N-terminal exonuclease domain connected by a linker region to a C-terminal polymerase domain. Whereas the exonuclease domain contains essential motifs I, II, and III for its activity, the polymerase domain comprising the thumb, palm, and finger subdomains contains motifs A, B, and C that are crucial for polymerase activity. The catalytic subunit is a family A DNA polymerase that includes bacterial pol I and T7 DNA polymerase and possesses DNA polymerase, 3′ → 5′ exonuclease, and 5′-deoxyribose phosphate lyase activities (for review, see Refs. 1 and 2). The 55-kDa accessory subunit (p55) confers processive DNA synthesis and tight binding of the pol γ complex to DNA (4, 5).Depletion of mtDNA as well as the accumulation of deletions and point mutations in mtDNA have been observed in several mitochondrial disorders (for review, see Ref. 6). mtDNA depletion syndromes are caused by defects in nuclear genes responsible for replication and maintenance of the mitochondrial genome (7). Mutation of POLG, the gene encoding the catalytic subunit of pol γ, is frequently involved in disorders linked to mutagenesis of mtDNA (8, 9). Presently, more than 150 point mutations in POLG are linked with a wide variety of mitochondrial diseases, including the autosomal dominant (ad) and recessive forms of progressive external ophthalmoplegia (PEO), Alpers syndrome, parkinsonism, ataxia-neuropathy syndromes, and male infertility (tools.niehs.nih.gov/polg) (9).Alpers syndrome, a hepatocerebral mtDNA depletion disorder, and myocerebrohepatopathy are rare heritable autosomal recessive diseases primarily affecting young children (10–12). These diseases generally manifest during the first few weeks to years of life, and symptoms gradually develop in a stepwise manner eventually leading to death. Alpers syndrome is characterized by refractory seizures, psychomotor regression, and hepatic failure (11, 12). Mutation of POLG was first linked to Alpers syndrome in 2004 (13), and to date 45 different point mutations in POLG (18 localized to the polymerase domain) are associated with Alpers syndrome (9, 14, 15). However, only two Alpers mutations (A467T and W748S, both in the linker region) have been biochemically characterized (16, 17).During the initial cloning and sequencing of the human, Drosophila, and chicken pol γ genes, we noted a highly conserved region N-terminal to motif A in the polymerase domain that was specific to pol γ (18). This region corresponds to part of the thumb subdomain that tracks DNA into the active site of both Escherichia coli pol I and T7 DNA polymerase (19–21). A high concentration of disease mutations, many associated with Alpers syndrome, is found in the thumb subdomain.Here we investigated six mitochondrial disease mutations clustered in the N-terminal portion of the polymerase domain of the enzyme (Fig. 1A). Four mutations (G848S, c.2542g→a; T851A, c.2551a→g; R852C, c.2554c→t; R853Q, c.2558g→a) reside in the thumb subdomain and two (Q879H, c.2637g→t and T885S, c.2653a→t) are located in the palm subdomain. These mutations are associated with Alpers, PEO, mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), ataxia-neuropathy syndrome, Leigh syndrome, and myocerebrohepatopathy (POLG mutation Disease Genetics Reference G848S Alpers syndrome In trans with A467T, Q497H, T251I-P587L, or W748S-E1143G in Alpers syndrome 15, 35, 43–50 Leigh syndrome In trans with R232H in Leigh syndrome 49 MELAS In trans with R627Q in MELAS 38 PEO with ataxia-neuropathy In trans with G746S and E1143G in PEO with ataxia 50 PEO In trans with T251I and P587L in PEO 51, 52 T851A Alpers syndrome In trans with R1047W 48, 53 In trans with H277C R852C Alpers syndrome In trans with A467T 14, 48, 50 In cis with G11D and in trans with W748S-E1143G or A467T Ataxia-neuropathy In trans with G11D-R627Q 15 R853Q Myocerebrohepatopathy In trans with T251I-P587L 15 Q879H Alpers syndrome with valproate-induced hepatic failure In cis with E1143G and in trans with A467T-T885S 35, 54 T885S Alpers syndrome with valproate-induced hepatic failure In cis with A467T and in trans with Q879H-E1143G 35, 54