Purification and characterization of a novel alcohol oxidase from Paenibacillus sp. AIU 311

Expression of alcohol oxidase gene from Ochrobactrum sp. AIU 033 in recombinant Escherichia coli through the twin-arginine translocation pathway

We cloned a set of genes encoding alcohol oxidase from Ochrobactrum sp. AIU 033 (OcAOD), which exhibits the appropriate substrate specificity for glyoxylic acid production from glycolic acid. The set of genes for OcAOD contained two open reading frames consisting of 555-bp (aodB) and 1572-bp (aodA) nucleotides, which encode the precursor for the β-subunit and α-subunit of OcAOD, respectively. We expressed the cloned genes as an active product in Escherichia coli BL21(DE3). The recombinant OcAOD oxidized glycolic acid and primary alcohols with C2-C8 but not glyoxylic acid (as is the case for native OcAOD), whereas the K_m and V_max values for glycolic acid and the pH stability were higher than those of native OcAOD. A consensus sequence for the twin-arginine translocation (Tat) pathway was identified in the N-terminal region of the precursor for the β-subunit, and the active form of OcAOD was localized in the periplasm of recombinant E. coli, which indicated that OcAOD would be transported from the cytoplasm to the periplasm by the hitchhiker mechanism through the Tat pathway. The OcAOD productivity of the recombinant E. coli was 24-fold higher than that of Ochrobactrum sp. AIU 033, and it was further enhanced by 1.2 times by the co-expression of additional tatABC from E. coli BL21(DE3). Our findings thus suggest a function of the β-subunit of OcAOD in membrane translocation, and that the recombinant OcAOD has characteristics that are suitable for the enzymatic synthesis of glyoxylic acid as well as native OcAOD.

Multi-catalysis reactions: new prospects and challenges of biotechnology to valorize lignin

Considerable effort has been dedicated to the chemical depolymerization of lignin, a biopolymer constituting a possible renewable source for aromatic value-added chemicals. However, these efforts yielded limited success up until now. Efficient lignin conversion might necessitate novel catalysts enabling new types of reactions. The use of multiple catalysts, including a combination of biocatalysts, might be necessary. New perspectives for the combination of bio- and inorganic catalysts in one-pot reactions are emerging, thanks to green chemistry-driven advances in enzyme engineering and immobilization and new chemical catalyst design. Such combinations could offer several advantages, especially by reducing time and yield losses associated with the isolation and purification of the reaction products, but also represent a big challenge since the optimal reaction conditions of bio- and chemical catalysis reactions are often different. This mini-review gives an overview of bio- and inorganic catalysts having the potential to be used in combination for lignin depolymerization. We also discuss key aspects to consider when combining these catalysts in one-pot reactions.

Microbial oxidases catalyzing conversion of glycolaldehyde into glyoxal

The present paper reviews oxidases catalyzing conversion of glycolaldehyde into glyoxal. The enzymatic oxidation of glycolaldehyde into glyoxal was first reported in alcohol oxidases (AODs) from methylotrophic yeasts such as Candida and Pichia, and glycerol oxidase (GLOD) from Aspergillus japonicus, although it had been reported that these enzymes are specific to short-chain linear aliphatic alcohols and glycerol, respectively. These enzymes continuously oxidized ethylene glycol into glyoxal via glycolaldehyde. The AODs produced by Aspergillus ochraceus and Penicillium purpurescens also oxidized glycolaldehyde. A new enzyme exhibiting oxidase activity for glycolaldehyde was reported from a newly isolated bacterium, Paenibacillus sp. AIU 311. The Paenibacillus enzyme exhibited high activity for aldehyde alcohols such as glycolaldehyde and glyceraldehyde, but not for methanol, ethanol, ethylene glycol or glycerol. The deduced amino acid sequence of the Paenibacillus AOD was similar to that of superoxide dismutases (SODs), but not to that of methylotrophic yeast AODs. Then, it was demonstrated that SODs had oxidase activity for aldehyde alcohols including glycolaldehyde. The present paper describes characteristics of glycolaldehyde oxidation by those enzymes produced by different microorganisms.

Cloning, sequencing and expression analysis of a gene encoding alcohol oxidase in Paenibacillus sp. AIU 311

We have cloned a gene encoding an alcohol oxidase (AOD) specific to aldehyde alcohols from Paenibacillus sp. AIU 311. The AOD gene contains an open reading frame consisting of 618 nucleotides corresponding to 205 amino acid residues. The deduced amino acid sequence exhibits a high similarity to that of manganese superoxide dismutases (SODs). We expressed the cloned gene as an active product in Escherichia coli BL21 cells. The productivity (total units per culture broth volume) of the recombinant AOD expressed in E. coli BL21 is 26,000-fold higher than that of AOD in Paenibacillus sp. AIU 311. The recombinant AOD also exhibits aldehyde alcohol oxidase activity and SOD activity. The recombinant cells described in this study have utility for the production of glyoxal from glycolaldehyde.