Cloning, heterologous expression, and characterization of a novel thioesterase from natural sample

AMWEst, a new thermostable and detergent-tolerant esterase retrieved from the Albian aquifer

A fosmid library was constructed with the metagenomic DNA from the high-temperature sediment-rich water of the Albian aquifer (Algeria). Functional screening of this library was subsequently done looking for genes encoding lipolytic enzymes. We identified a novel gene named AMWEst (1209 base pairs) encoding a protein of 402 amino acids with a predicted molecular weight of 43.44 kDa and conferring esterase activity. AMWEst was successfully overexpressed in the yeast mesophilic host Saccharomyces cerevisiae, and the expression system used proved to be efficient and produced sufficient activity for its biochemical characterization. Multiple sequence alignment indicated that AMWEst contained a conserved pentapeptide motif (Gly120-His121-Ser122-Gln123-Gly124). The optimum pH and temperature of the recombinant esterase AMWEst were 8 and 80 °C, respectively. Additionally, AMWEst showed higher activity towards short carbon substrates and showed maximum activity for p-nitrophenyl hexanoate (C6). Notably, AMWEst has a remarkable thermostability, and the enzyme retains almost maximum activity at 70 °C after incubation for 1 h. Moreover, enzyme activity was enhanced by high concentrations of SDS and Triton X-100 detergents. KEY POINTS: • A novel thermostable esterase has been retrieved through functional metagenomics • The esterase is detergent-tolerant, which is attractive for some applications • The esterase can be expressed in a yeast mesophilic host to enhance its yield.

A strategy to enhance and modify fatty acid synthesis in Corynebacterium glutamicum and Escherichia coli: overexpression of acyl-CoA thioesterases

BACKGROUND

Fatty acid (FA) is an important platform compound for the further synthesis of high-value biofuels and oleochemicals, but chemical synthesis of FA has many limitations. One way to meet the future demand for FA could be to use microbial cell factories for FA biosynthesis.

RESULTS

Thioesterase (TE; TesA, TesB, and TE9) of Corynebacterium glutamicum (CG) can potentially improve FA biosynthesis, and tesA, tesB, and te9 were overexpressed in C. glutamicum and Escherichia coli (EC), respectively, in this study. The results showed that the total fatty acid (TFA) production of CGtesB and ECtesB significantly increased to 180.52 mg/g dry cell weight (DCW) and 123.52 mg/g DCW, respectively (P < 0.05). Overexpression strains CG and EC could increase the production of C16:0, C18:1(t), C18:2, C20:1, C16:1, C18:0, and C18:1(c) (P < 0.05), respectively, and the changes of long-chain FA resulted in the enhancement of TFA production. The enzymatic properties of TesA, TesB, and TE9 in vitro were determined: they were specific for long-, broad and short-chain substrates, respectively; the optimal temperature was 30.0 °C and the optimal acid-base (pH) were 8.0, 8.0, and 9.0, respectively; they were inhibited by Fe2+, Cu2+, Zn2+, Mg2+, and K+.

CONCLUSION

Overexpression TE enhances and modifies FA biosynthesis with multiple productive applications, and the enzyme properties provided useful clues for optimizing FA synthesis.

Characterization of thermostable serine hydroxymethyltransferase for β-hydroxy amino acids synthesis

β-hydroxy amino acids, such as serine, threonine, and phenylserine, are important compounds for medical purposes. To date, there has been only limited exploration of thermostable serine hydroxylmethyltransferase (SHMT) for the synthesis of these amino acids, despite the great potential that thermostable enzymes may offer for commercial use due to their high stability and catalytic efficiencies. ITBSHMT_1 (ITB serine hydroxylmethyltransferase clone number 1) from thermophilic and methanol-tolerant bacteria Pseudoxanthomonas taiwanensis AL17 was successfully cloned. Biocomputational analysis revealed that ITBSHMT_1 contains Pyridoxal-3'-phosphate and tetrahydrofolatebinding residues. Structural comparisons show that ITBSHMT_1 has 5 additional residues VSRQG on loop near PLP-binding site as novel structural feature which distinguish this enzyme with other characterized SHMTs. In silico mutation revealed that the fragment might have very essential role in maintaining of PLP binding on structure of ITBSHMT_1. Recombinant protein was produced in Escherichia coli Rosetta 2(DE3) in soluble form and purified using NiNTA affinity chromatography. The purified protein demonstrated the best activity at 80 °C and pH 7.5 based on the retro aldol cleavage of phenylserine. Activity decreased significantly in the presence of 3 mM transition metal ions but increased in the presence of 30 mM β-mercaptoethanol. ITBSHMT_1 demonstrated Vmax, Km, Kcat, and Kcat/Km at 242 U/mg, 23.26 mM, 186/s, and 8/(mM.s), respectively. The aldol condensation reaction showed the enzyme's best activity at 80 °C for serine, threonine, or phenylserine, with serine synthesis showing the highest specific activity. Biocomputational analysis revealed that high intramolecular interaction within the 3D structure of ITBSHMT_1 might be correlated with the enzyme's high thermal stability. The above data suggest that ITBSHMT_1 is a potential and novel enzyme for the production of various β-hydroxy amino acids.