Explore the vast range of titles available.

Continuous low-level supply or in situ generation of hydrogen peroxide (H 2 O 2 ) is essential for the stability of unspecific peroxygenases, which are deemed ideal biocatalysts for the selective activation of C–H bonds. To envisage potential large scale applications of combined catalytic systems the reactions need to be simple, efficient and produce minimal by-products. We show that gold-palladium nanoparticles supported on TiO 2 or carbon have sufficient activity at ambient temperature and pressure to generate H 2 O 2 from H 2 and O 2 and supply the oxidant to the engineered unspecific heme-thiolate peroxygenase PaDa-I. This tandem catalyst combination facilitates efficient oxidation of a range of C-H bonds to hydroxylated products in one reaction vessel with only water as a by-product under conditions that could be easily scaled. Continuous low-level supply or in situ generation of hydrogen peroxide (H 2 O 2 ) is essential for the stability of unspecific peroxygenases. Here, the authors demonstrate that AuPd / TiO 2 can generate sufficient H 2 O 2 for the engineered unspecific heme-thiolate peroxygenase PaDa-I to oxidise a range of C-H bonds.

Background The regeneration of cofactors and the supply of alkane substrate are key considerations for the biocatalytic activation of hydrocarbons by cytochrome P450s. This study focused on the biotransformation of n-octane to 1-octanol using resting Escherichia coli cells expressing the CYP153A6 operon, which includes the electron transport proteins ferredoxin and ferredoxin reductase. Glycerol dehydrogenase was co-expressed with the CYP153A6 operon to investigate the effects of boosting cofactor regeneration. In order to overcome the alkane supply bottleneck, various chemical and physical approaches to membrane permeabilisation were tested in strains with or without additional dehydrogenase expression. Results Dehydrogenase co-expression in whole cells did not improve product formation and reduced the stability of the system at high cell densities. Chemical permeabilisation resulted in initial hydroxylation rates that were up to two times higher than the whole cell system, but severely impacted biocatalyst stability. Mechanical cell breakage led to improved enzyme stability, but additional dehydrogenase expression was necessary to improve product formation. The best-performing system (in terms of final titres) consisted of mechanically ruptured cells expressing additional dehydrogenase. This system had an initial activity of 1.67 ± 0.12 U/g DCW (32% improvement on whole cells) and attained a product concentration of 34.8 ± 1.6 mM after 24 h (22% improvement on whole cells). Furthermore, the system was able to maintain activity when biotransformation was extended to 72 h, resulting in a final product titre of 60.9 ± 1.1 mM. Conclusions This study suggests that CYP153A6 in whole cells is limited by coupling efficiencies rather than cofactor supply. However, the most significant limitation in the current system is hydrocarbon transport, with substrate import being the main determinant of hydroxylation rates, and product export playing a key role in system stability.

Background Biocatalyst improvement through molecular and recombinant means should be complemented with efficient process design to facilitate process feasibility and improve process economics. This study focused on understanding the bioprocess limitations to identify factors that impact the expression of the terminal hydroxylase CYP153A6 and also influence the biocatalytic transformation of n –octane to 1-octanol using resting whole cells of recombinant E . coli expressing the CYP153A6 operon which includes the ferredoxin (Fdx) and the ferredoxin reductase (FdR). Results Specific hydroxylation activity decreased with increasing protein expression showing that the concentration of active biocatalyst is not the sole determinant of optimum process efficiency. Process physiological conditions including the medium composition, temperature, glucose metabolism and product toxicity were investigated. A fed-batch system with intermittent glucose feeding was necessary to ease overflow metabolism and improve process efficiency while the introduction of a product sink (BEHP) was required to alleviate octanol toxicity. Resting cells cultivated on complex LB and glucose-based defined medium with similar CYP level (0.20 μmol g DCW -1 ) showed different biocatalyst activity and efficiency in the hydroxylation of octane over a period of 120 h. This was influenced by differing glucose uptake rate which is directly coupled to cofactor regeneration and cell energy in whole cell biocatalysis. The maximum activity and biocatalyst efficiency achieved presents a significant improvement in the use of CYP153A6 for alkane activation. This biocatalyst system shows potential to improve productivity if substrate transfer limitation across the cell membrane and enzyme stability can be addressed especially at higher temperature. Conclusion This study emphasises that the overall process efficiency is primarily dependent on the interaction between the whole cell biocatalyst and bioprocess conditions.

During the COVID-19 pandemic, access to vaccines in low- and middle-income countries was limited and delayed. To address these disparities, the mRNA Technology Transfer Programme, coordinated and led by the World Health Organization and the Medicines Patent Pool, was launched. A consortium has been set up in South Africa to develop a platform for manufacturing mRNA vaccines. In this study, the preclinical evaluation of the mRNA COVID-19 vaccine candidate, AfriVac 2121 (Wuhan) manufactured in December 2022 was conducted. The hamster model was employed to assess the immunogenicity and efficacy of this COVID-19 mRNA vaccine candidate in comparison to a commercial mRNA vaccine (mRNA-1273, Moderna). Results revealed that a vaccine regimen consisting of two 5 μg doses of AfriVac 2121 (Wuhan) elicited a protective immune response against an ancestral B.1 strain of SARS-CoV-2 similar to that obtained with the mRNA-1273 vaccine. AfriVac 2121 (Wuhan) induced robust humoral immune responses against SARS-CoV-2 and protected hamsters against a SARS-CoV-2 challenge with the B.1 strain. These results have since enabled the further development of this platform for manufacturing mRNA vaccines. •To address disparities in access to vaccines during the COVID-19 pandemic, the mRNA Technology Transfer Programme was launched by the WHO and MPP.l.•In 2022, the resulting Drug Product AfriVac 2121 (Wuhan) was subjected to immunological and efficacy evaluation in pre-clinical model.•The AfriVac 2121 (Wuhan) vaccine elicits robust humoral immune responses against SARS-CoV-2 in hamster model.•The AfriVac 2121 (Wuhan) vaccine protects hamsters against SARS-CoV-2 challenge with a B.1 SARS-CoV-2 stain in hamster model.

Continuous low-level supply or in situ generation of hydrogen peroxide (H O ) is essential for the stability of unspecific peroxygenases, which are deemed ideal biocatalysts for the selective activation of C-H bonds. To envisage potential large scale applications of combined catalytic systems the reactions need to be simple, efficient and produce minimal by-products. We show that gold-palladium nanoparticles supported on TiO or carbon have sufficient activity at ambient temperature and pressure to generate H O from H and O and supply the oxidant to the engineered unspecific heme-thiolate peroxygenase PaDa-I. This tandem catalyst combination facilitates efficient oxidation of a range of C-H bonds to hydroxylated products in one reaction vessel with only water as a by-product under conditions that could be easily scaled.