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Engineering Klebsiella sp. 601 multicopper oxidase enhances the catalytic efficiency towards phenolic substrates.

ABSTRACT: BACKGROUND: Structural comparison between bacterial CueO and fungal laccases has suggested that a charged residue Glu (E106) in CueO replaces the corresponding residue Phe in fungal laccases at the gate of the tunnel connecting type II copper to the protein surface and an extra ?-helix (L351-G378) near the type I copper site covers the substrate binding pocket and might compromise the electron transfer from substrate to type I copper. To test this hypothesis, several mutants were made in Klebsiella sp. 601 multicopper oxidase, which is highly homologous to E. coli CueO with a similarity of 90% and an identity of 78%. RESULTS: The E106F mutant gave smaller K(m) (2.4-7 fold) and k(cat) (1-4.4 fold) values for all three substrates DMP, ABTS and SGZ as compared with those for the wild-type enzyme. Its slightly larger k(cat)/K(m) values for three substrates mainly come from the decreased K(m). Deleting ?-helix (L351-G378) resulted in the formation of inactive inclusion body when the mutant (?)?351-378 was expressed in E. coli. Another mutant ?351-380M was then made via substitution of seven amino acid residues in the ?-helix (L351-G378) region. The ?351-380M mutant was active, and displayed a far-UV CD spectrum markedly different from that for wild-type enzyme. Kinetic studies showed the ?351-380M mutant gave very low K(m) values for DMP, ABTS and SGZ, 4.5-, 1.9- and 7-fold less than those for the wild type. In addition, k(cat)/K(m) values were increased, 9.4-fold for DMP, similar for ABTS and 3-fold for SGZ. CONCLUSION: The Glu residue at position 106 appears not to be the only factor affecting the copper binding, and it may also play a role in maintaining enzyme conformation. The ?-helix (L351-G378) may not only block access to the type I copper site but also play a role in substrate specificities of bacterial MCOs. The ?351-380M mutant catalyzing oxidation of the phenolic substrate DMP effectively would be very useful in green chemistry.

SUBMITTER: Li Y

PROVIDER: S-EPMC3123277 | biostudies-literature | 2011

REPOSITORIES: biostudies-literature

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Engineering Klebsiella sp. 601 multicopper oxidase enhances the catalytic efficiency towards phenolic substrates.

Li Yadong Y Gong Zijun Z Li Xin X Li Yang Y Wang Xing-Guo XG

BMC biochemistry 20110531

<h4>Background</h4>Structural comparison between bacterial CueO and fungal laccases has suggested that a charged residue Glu (E106) in CueO replaces the corresponding residue Phe in fungal laccases at the gate of the tunnel connecting type II copper to the protein surface and an extra α-helix (L351-G378) near the type I copper site covers the substrate binding pocket and might compromise the electron transfer from substrate to type I copper. To test this hypothesis, several mutants were made in ...[more]

PMID: 21624144

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Project description:Multicopper oxidases (MCOs) are a family of enzymes that use copper ions as cofactors to oxidize various substrates. Previous research has demonstrated that several MCOs such as MnxG, MofA and MoxA can act as putative Mn(II) oxidases. Meanwhile, the endospore coat protein CotA from Bacillus species has been confirmed as a typical MCO. To study the relationship between CotA and the Mn(II) oxidation, the cotA gene from a highly active Mn(II)-oxidizing strain Bacillus pumilus WH4 was cloned and overexpressed in Escherichia coli strain M15. The purified CotA contained approximately four copper atoms per molecule and showed spectroscopic properties typical of blue copper oxidases. Importantly, apart from the laccase activities, the CotA also displayed substantial Mn(II)-oxidase activities both in liquid culture system and native polyacrylamide gel electrophoresis. The optimum Mn(II) oxidase activity was obtained at 53°C in HEPES buffer (pH 8.0) supplemented with 0.8 mM CuCl2. Besides, the addition of o-phenanthroline and EDTA both led to a complete suppression of Mn(II)-oxidizing activity. The specific activity of purified CotA towards Mn(II) was 0.27 U/mg. The Km, Vmax and kcat values towards Mn(II) were 14.85±1.17 mM, 3.01×10(-6)±0.21 M·min(-1) and 0.32±0.02 s(-1), respectively. Moreover, the Mn(II)-oxidizing activity of the recombinant E. coli strain M15-pQE-cotA was significantly increased when cultured both in Mn-containing K liquid medium and on agar plates. After 7-day liquid cultivation, M15-pQE-cotA resulted in 18.2% removal of Mn(II) from the medium. Furthermore, the biogenic Mn oxides were clearly observed on the cell surfaces of M15-pQE-cotA by scanning electron microscopy. To our knowledge, this is the first report that provides the direct observation of Mn(II) oxidation with the heterologously expressed protein CotA, Therefore, this novel finding not only establishes the foundation for in-depth study of Mn(II) oxidation mechanisms, but also offers a potential biocatalyst for Mn(II) removal.

Project description:The multicopper oxidase (MCO) family of enzymes includes laccases, which oxidize a broad range of substrates including diphenols, and several oxidases with specific substrates such as iron, copper or ascorbic acid. We have identified five putative MCO genes in the genome of Anopheles gambiae and have cloned cDNAs encompassing the full coding region for each gene. MCO1 mRNA was detected in all developmental stages and in all of the larval and adult tissues tested. We observed an increase in MCO1 transcript abundance in the midguts and Malphighian tubules of adult females following a blood meal and in adult abdominal carcasses in response to an immune challenge. Two alternatively spliced isoforms of MCO2 mRNA were identified. The A isoform of MCO2 was previously detected in larval and pupal cuticle where it probably catalyzes sclerotization reactions (He, N., Botelho, J.M.C., McNall, R.J., Belozerov, V., Dunn, W.A., Mize, T., Orlando, R., Willis, J.H., 2007. Proteomic analysis of cast cuticles from Anopheles gambiae by tandem mass spectrometry. Insect Biochem. Mol. Biol. 37, 135-146). The B isoform was transcriptionally upregulated in ovaries in response to a blood meal. MCO3 mRNA was detected in the adult midgut, Malpighian tubules, and male reproductive tissues; like MCO1, it was upregulated in response to an immune challenge or a blood meal. MCO4 and MCO5 were observed primarily in eggs and in the abdominal carcass of larvae. A phylogenetic analysis of insect MCO genes identified putative orthologs of MCO1 and MCO2 in all of the insect genomes tested, whereas MCO3, MCO4 and MCO5 were found only in the two mosquito species analyzed. MCO2 orthologs have especially high sequence similarity, suggesting that they are under strong purifying selection; the A isoforms are more conserved than the B isoforms. The mosquito specific group shares a common ancestor with MCO2. This initial study of mosquito MCOs suggests that MCO2 may be required for egg development or eggshell tanning in addition to cuticle tanning, while MCO1 and MCO3 may be involved in metal metabolism or immunity.

Dataset Information

Engineering Klebsiella sp. 601 multicopper oxidase enhances the catalytic efficiency towards phenolic substrates.

Publications

Engineering Klebsiella sp. 601 multicopper oxidase enhances the catalytic efficiency towards phenolic substrates.

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