Microbial catabolism of vanillate: decarboxylation to guaiacol.
(1/97)
A novel catabolic transformation of vanillic acid (4-hydroxy-3-methoxybenzoic acid) by microorganisms is reported. Several strains of Bacillus megaterium and a strain of Streptomyces are shown to convert vanillate to guaiacol (o-methoxyphenol) and CO2 by nonoxidative decarboxylation. Use of a modified most-probable-number procedure shows that numerous soils contain countable numbers (10(1) to 10(2) organisms per g of dry soil) of aerobic sporeformers able to convert vanillate to guaiacol. Conversion of vanillate to guaiacol by the microfloras of most-probable-number replicates was used as the criterion for scoring replicates positive or negative. Guaiacol was detected by thin-layer chromatography. These results indicate that the classic separations of catabolic pathways leading to specific ring-fashion substrates such as protocatechuate and catechol are often interconnectable by single enzymatic transformations, usually a decarboxylation. (+info)
Genetic analysis of a chromosomal region containing vanA and vanB, genes required for conversion of either ferulate or vanillate to protocatechuate in Acinetobacter.
(2/97)
VanA and VanB form an oxygenative demethylase that converts vanillate to protocatechuate in microorganisms. Ferulate, an abundant phytochemical, had been shown to be metabolized through a vanillate intermediate in several Pseudomonas isolates, and biochemical evidence had indicated that vanillate also is an intermediate in ferulate catabolism by Acinetobacter. Genetic evidence supporting this conclusion was obtained by characterization of mutant Acinetobacter strains blocked in catabolism of both ferulate and vanillate. Cloned Acinetobacter vanA and vanB were shown to be members of a chromosomal segment remote from a supraoperonic cluster containing other genes required for completion of the catabolism of ferulate and its structural analogs, caffeate and coumarate, through protocatechuate. The nucleotide sequence of DNA containing vanA and vanB demonstrated the presence of genes that, on the basis of nucleotide sequence similarity, appeared to be associated with transport of aromatic compounds, metabolism of such compounds, or iron scavenging. Spontaneous deletion of 100 kb of DNA containing this segment does not impede the growth of cells with simple carbon sources other than vanillate or ferulate. Additional spontaneous mutations blocking vanA and vanB expression were shown to be mediated by IS1236, including insertion of the newly discovered composite transposon Tn5613. On the whole, vanA and vanB appear to be located within a nonessential genetic region that exhibits considerable genetic malleability in Acinetobacter. The overall organization of genes neighboring Acinetobacter vanA and vanB, including a putative transcriptional regulatory gene that is convergently transcribed and overlaps vanB, is conserved in Pseudomonas aeruginosa but has undergone radical rearrangement in other Pseudomonas species. (+info)
The physiological contribution of Acinetobacter PcaK, a transport system that acts upon protocatechuate, can be masked by the overlapping specificity of VanK.
(3/97)
VanK is the fourth member of the ubiquitous major facilitator superfamily of transport proteins to be identified that, together with PcaK, BenK, and MucK, contributes to aromatic catabolism in Acinetobacter sp. strain ADP1. VanK and PcaK have overlapping specificity for p-hydroxybenzoate and, most clearly, for protocatechuate: inactivation of both proteins severely impairs growth with protocatechuate, and the activity of either protein alone can mask the phenotype associated with inactivation of its homolog. Furthermore, vanK pcaK double-knockout mutants appear completely unable to grow in liquid culture with the hydroaromatic compound quinate, although such cells on plates convert quinate to protocatechuate, which then accumulates extracellularly and is readily visible as purple staining. This provides genetic evidence that quinate is converted to protocatechuate in the periplasm and is in line with the early argument that quinate catabolism should be physically separated from aromatic amino acid biosynthesis in the cytoplasm so as to avoid potential competition for intermediates common to both pathways. Previous studies of aromatic catabolism in Acinetobacter have taken advantage of the ability to select directly strains that contain a spontaneous mutation blocking the beta-ketoadipate pathway and preventing the toxic accumulation of carboxymuconate. By using this procedure, strains with a mutation in structural or regulatory genes blocking degradation of vanillate, p-hydroxybenzoate, or protocatechuate were selected. In this study, the overlapping specificity of the VanK and PcaK permeases was exploited to directly select strains with a mutation in either vanK or pcaK. Spontaneous mutations identified in vanK include a hot spot for frameshift mutation due to contraction of a G6 mononucleotide repeat as well as point mutations producing amino acid substitutions useful for analysis of VanK structure and function. Preliminary second-site suppression analysis using transformation-facilitated PCR mutagenesis in one VanK mutant gave results similar to those using LacY, the prototypic member of the major facilitator superfamily, consistent with the two proteins having a similar mechanism of action. The selection for transport mutants described here for Acinetobacter may also be applicable to Pseudomonas putida, where the PcaK permease has an additional role in chemotaxis. (+info)
The cloned rat vanilloid receptor VR1 mediates both R-type binding and C-type calcium response in dorsal root ganglion neurons.
(4/97)
[(3)H]Resiniferatoxin (RTX) binding and calcium uptake by rat dorsal root ganglion (DRG) neurons show distinct structure-activity relations, suggestive of independent vanilloid receptor (VR) subtypes. We have now characterized ligand binding to rat VR1 expressed in human embryonic kidney (HEK293) and Chinese hamster ovary (CHO) cells and compared the structure-activity relations with those for calcium mobilization. Human embryonic kidney cells (HEK293/VR1 cells) and Chinese hamster ovary cells transfected with VR1 (CHO/VR1 cells) bound [(3)H]RTX with affinities of 84 and 103 pM, respectively, and positive cooperativity (Hill numbers were 2.1 and 1.8). These parameters are similar to those determined with rat DRG membranes expressing native VRs (a K(d) of 70 pM and a Hill number of 1.7). The typical vanilloid agonists olvanil and capsaicin inhibited [(3)H]RTX binding to HEK293/VR1 cells with K(i) values of 0.4 and 4.0 microM, respectively. The corresponding values in DRG membranes were 0.3 and 2.5 microM. HEK293/VR1 cells and DRG membranes also recognized the novel vanilloids isovelleral and scutigeral with similar K(i) values (18 and 20 microM in HEK293/VR1 cells; 24 and 21 microM in DRGs). The competitive vanilloid receptor antagonist capsazepine inhibited [(3)H]RTX binding to HEK293/VR1 cells with a K(i) value of 6.2 microM and binding to DRG membranes with a K(i) value of 8.6 microM. RTX and capsaicin induced calcium mobilization in HEK293/VR1 cells with EC(50) values of 4.1 and 82 nM, respectively. Thus, the relative potencies of RTX (more potent for binding) and capsaicin (more potent for calcium mobilization) are similar in DRG neurons and cells transfected with VR1. We conclude that VR1 can account for both the ligand binding and calcium uptake observed in rat DRG neurons. (+info)
Characterization of a vanillic acid non-oxidative decarboxylation gene cluster from Streptomyces sp. D7.
(5/97)
The genetics of non-oxidative decarboxylation of aromatic acids are poorly understood in both prokaryotes and eukaryotes. Although such reactions have been observed in numerous micro-organisms acting on a variety of substrates, the genes encoding enzymes responsible for these processes have not, to our knowledge, been reported in the literature. Here, the isolation of a streptomycete from soil (Streptomyces sp. D7) which efficiently converts 4-hydroxy-3-methoxybenzoic acid (vanillic acid) to 2-methoxyphenol (guaiacol) is described. Protein two-dimensional gel analysis revealed that several proteins were synthesized in response to vanillic acid. One of these was characterized by partial amino-terminal sequencing, leading to the cloning of a gene cluster from a genomic DNA lambda phage library, consisting of three ORFs, vdcB (602 bp), vdcC (1424 bp) and vdcD (239 bp). Protein sequence comparisons suggest that the product of vdcB (201 aa) is similar to phenylacrylate decarboxylase of yeast; the putative products of vdcC (475 aa) and vdcD (80 aa) are similar to hypothetical proteins of unknown function from various micro-organisms, and are found in a similar cluster in Bacillus subtilis. Northern blot analysis revealed the synthesis of a 2.5 kb mRNA transcript in vanillic-acid-induced cells, suggesting that the cluster is under the control of a single inducible promoter. Expression of the entire vdc gene cluster in Streptomyces lividans 1326 as a heterologous host resulted in that strain acquiring the ability to decarboxylate vanillic acid to guaiacol non-oxidatively. Both Streptomyces sp. strain D7 and recombinant S. lividans 1326 expressing the vdc gene cluster do not, however, decarboxylate structurally similar aromatic acids, suggesting that the system is specific for vanillic acid. This catabolic system may be useful as a component for pathway engineering research focused towards the production of valuable chemicals from forestry and agricultural by-products. (+info)
Veratryl alcohol-mediated oxidation of isoeugenyl acetate by lignin peroxidase.
(6/97)
The mechanism of the veratryl alcohol (VA)-mediated oxidation of isoeugenyl acetate (IEA) by lignin peroxidase, and the subsequent spontaneous Calpha-Cbeta cleavage of IEA to vanillyl acetate were studied. IEA oxidation only occurred in the presence of VA. It probably did not bind to lignin peroxidase as evidenced by an unaffected Km for VA in the presence of IEA, and by the fact that a 10-fold molar excess of the unreactive IEA counterpart, eugenyl acetate, did not affect the IEA oxidation rate. IEA was very efficient in recycling VA. Up to 34 mol of IEA were oxidized per mol VA. Formation of the predominant VA oxidation product, veratraldehyde, was postponed until IEA was almost completely oxidized. Together these findings suggest that IEA was oxidized by VA.+ rather than directly by lignin peroxidase. Thus, VA functioned as a redox mediator during IEA oxidation which is remarkable considering the high calculated ionization potential of 8.81 eV. Regardless of the presence of O2, approximately 2 mol of IEA were consumed per mol H2O2, which indicated that IEA was enzymatically oxidized by one electron to the putative radical cation (IEA.+). After formation of IEA.+, a series of O2-dependent chemical reactions were responsible for Calpha-Cbeta cleavage to the major oxidation product vanillyl acetate, as evidenced by the observation that an N2 atmosphere did not inhibit IEA oxidation, but almost completely inhibited vanillyl acetate formation. GC-MS analyses revealed that under an air atmosphere 1-(4'-acetoxy-3'-methoxyphenyl)-2-propanone, 1-(4'-acetoxy-3'-methoxyphenyl)-1-hydroxy-2-propanone, and 1-(4'-acetoxy-3'-methoxyphenyl)-2-hydroxy-1-propanone were also formed. Formation of the latter two was diminished under an N2 atmosphere. (+info)
Biocatalytic synthesis of vanillin.
(7/97)
The conversions of vanillic acid and O-benzylvanillic acid to vanillin were examined by using whole cells and enzyme preparations of Nocardia sp. strain NRRL 5646. With growing cultures, vanillic acid was decarboxylated (69% yield) to guaiacol and reduced (11% yield) to vanillyl alcohol. In resting Nocardia cells in buffer, 4-O-benzylvanillic acid was converted to the corresponding alcohol product without decarboxylation. Purified Nocardia carboxylic acid reductase, an ATP and NADPH-dependent enzyme, quantitatively reduced vanillic acid to vanillin. Structures of metabolites were established by (1)H nuclear magnetic resonance and mass spectral analyses. (+info)
Substrate range and genetic analysis of Acinetobacter vanillate demethylase.
(8/97)
An Acinetobacter sp. genetic screen was used to probe structure-function relationships in vanillate demethylase, a two-component monooxygenase. Mutants with null, leaky, and heat-sensitive phenotypes were isolated. Missense mutations tended to be clustered in specific regions, most of which make known contributions to catalytic activity. The vanillate analogs m-anisate, m-toluate, and 4-hydroxy-3,5-dimethylbenzoate are substrates of the enzyme and weakly inhibit the metabolism of vanillate by wild-type Acinetobacter bacteria. PCR mutagenesis of vanAB, followed by selection for strains unable to metabolize vanillate, yielded mutant organisms in which vanillate metabolism is more strongly inhibited by the vanillate analogs. Thus, the procedure opens for investigation amino acid residues that may contribute to the binding of either vanillate or its chemical analogs to wild-type and mutant vanillate demethylases. Selection of phenotypic revertants following PCR mutagenesis gave an indication of the extent to which amino acid substitutions can be tolerated at specified positions. In some cases, only true reversion to the original amino acid was observed. In other examples, a range of amino acid substitutions was tolerated. In one instance, phenotypic reversion failed to produce a protein with the original wild-type sequence. In this example, constraints favoring certain nucleotide substitutions appear to be imposed at the DNA level. (+info)