Production of phenylpyruvic acid by engineered l-amino acid deaminase from Proteus mirabilis

Effect of hexavalent chromium on growth performance and metabolism in broiler chicken

Hexavalent chromium Cr (VI) is one of the most hazardous heavy metals in the environment and is toxic to living organisms causing tissue damage, disruption of the intestinal microbiota and cancer. However, there is little information on the relationship between the Cr (VI) and broiler chickens. The current study was performed to investigate the effect of Cr (VI) on growth performance, serum biochemical analysis, histopathological observations, and metabolomics analysis in broilers. Results show that Cr (VI) exposure significantly decreased the body weight (p < 0.01) and caused liver damages in broilers. With the extension of Cr (VI) action time, the liver appeared obvious pathological changes, including hepatic cord disorder, incomplete hepatocyte additionally, decreased serum biochemical indices of calcium (Ca), phosphorus (P), total protein (TP), phosphatase (ALP), and globin (GLB) significantly (p < 0.01). Moreover, metabolomics analysis indicated that 29 differential metabolites were identified, such as phytosphingosine, L-Serine, 12, 13-DHOME, Alpha-dimorphecolic acid, L-Methionine, L-Phenylalanine, 3-Dehydroshikimate, L-Tyrosine, and N-Acetyl-L-phenylalanine were significantly decreased under the action of Cr (VI) (p < 0.05). These 29 differential metabolites are mainly involved in 35 metabolic pathways, such as aminoacyl-tRNA biosynthesis, phenylalanine metabolism, sphingolipid, and linoleic metabolism. The study revealed that exposure to Cr (VI) resulted in a decrease in growth performance and metabolism, with the hazards and toxicity in broiler chicken. The findings provided new insight and a comprehensive understanding of the relationship between Cr (VI) and broiler chickens.

Semi-rational engineering membrane binding domain of L-amino acid deaminase from Proteus vulgaris for enhanced α-ketoisocaproate

α-Keto acids are important raw materials for pharmaceuticals and functional foods, which could be produced from cheap feed stock by whole cell biocatalysts containing L-amino acid deaminases (L-AADs). However, the production capacity is limited by the low activity of L-AADs. The L-AAD mediated redox reaction employs the electron transport chain to transfer electrons from the reduced FADH₂ to O₂, implying that the interaction between L-AAD and the cell membrane affects its catalytic activity. To improve the catalytic activity of L-AAD from Proteus vulgaris, we redesigned the membrane-bound hydrophobic insertion sequences (INS, residues 325–375) by saturation mutagenesis and high-throughput screening. Mutants D340N and L363N exhibited higher affinity and catalytic efficiency for L-leucine, with half-life 1.62-fold and 1.28-fold longer than that of wild-type L-AAD. D340N catalyzed L-leucine to produce 81.21 g⋅L^–1 α-ketoisocaproate, with a bioconversion rate of 89.06%, which was 17.57% higher than that of the wild-type. It is predicted that the mutations enhanced the interaction between the protein and the cell membrane.

Efficient whole cell biotransformation of tyrosol from L-tyrosine by engineered Escherichia coli

An engineered Escherichia coli was constructed by co-expressing L-amino acid deaminase, α-keto acid decarboxylase, alcohol dehydrogenase, and glucose dehydrogenase through two plasmids for tyrosol production. The activity of the rate-limiting enzyme L-amino acid deaminase from Cosenzaea myxofaciens (CmAAD) toward tyrosine was improved by structure-guided modification. The enzyme activity of triple mutant CmAAD V438G/K147V/R151E toward tyrosine was ~5.12-fold higher than that of the wild-type CmAAD. Secondly, the plasmid copy numbers and the gene orders were optimized to improve the titer of tyrosol. Finally, the recombinant strain CS-6 transformed 10 mM tyrosine into 9.56 ± 0.64 mM tyrosol at 45 ℃, and the space-time yield reached 0.478 mM·L^-1·h^-1. This study proposes a novel idea for the efficient and natural production of tyrosol, which has great potential for industrial application.