Novel expression system based on enhanced permeability of Vibrio natriegens cells induced by D,D- carboxypeptidase overexpression

Vibrio natriegens is a fast-growing, non-pathogenic marine bacterium with promising features for biotechnological applications such as high-level recombinant protein production or fast DNA propagation. A remarkable short generation time (< 10 min), robust proteosynthetic activity and versatile metabolism with abilities to utilise wide range of substrates contribute to its establishment as a future industrial platform for fermentation processes operating with high productivity.D,D-carboxypeptidases are membrane-associated enzymes involved in peptidoglycan biosynthesis and cell wall formation. This study investigates the impact of overexpressed D,D-carboxypeptidases on membrane integrity and the increased leakage of intracellular proteins into the growth medium in V. natriegens. Our findings confirm that co-expression of these enzymes can enhance membrane permeability, thereby facilitating the transport of target proteins into the extracellular environment, without the need for secretion signals, tags, or additional permeabilization methods. Using only a single step IMAC chromatography, we were able to purify AfKatG, MDBP or Taq polymerase in total yields of 117.9 ± 56.0 mg/L, 36.5 ± 12.9 mg/L and 26.5 ± 6.0 mg/L directly from growth medium, respectively. These results demonstrate the feasibility of our V. natriegens based system as a broadly applicable extracellular tag-less recombinant protein producer.

Enhancement of solubility of recombinant alcohol dehydrogenase from Rhodococcus ruber using predictive tool

Solubility is one of key factors influencing the heterologous production of recombinant proteins in biotechnology. Among many aggregation-prone proteins, alcohol dehydrogenase (ADH-A) from Rhodococcus ruber (in this work abbreviated RrADH) shows a great potential in processes involved in the biotransformation of natural compounds. As ADH-A is a potentially high value asset in industrial biotransformation processes, improvement of its solubility would be of major commercial benefit. Predictive tools and in silico analysis provide a fast means for improving protein properties, for selecting appropriate changes, and ultimately for saving costs. We have therefore focused on enhancement of the solubility of RrADH using an online accesible predictive tool Aggrescan 3D 2.0. Selected mutations were introduced into the protein amino acid sequence by using site-directed PCR. This led to a 17% increase in the protein solubility of RrADHmut1 and a 98% increase for RrADHmut2. Moreover, the basic kinetics of the enzyme reaction were positively affected, further optimizing the overall performance of the production process.

Complex Analysis of Vanillin and Syringic Acid as Natural Antimicrobial Agents against Staphylococcus epidermidis Biofilms

The presence of Staphylococcus epidermidis biofilms on medical devices is a major cause of nosocomial diseases and infections. Extensive research is directed at inhibiting the formation and maturation of such biofilms. Natural plant-derived phenolic compounds have promising antimicrobial effects against drug-resistant bacteria. The anti-biofilm activity of two selected phenolic compounds (vanillin and syringic acid) was tested against three biofilm-forming methicillin-resistant S. epidermidis strains with different genotypes. Resazurin assay combining crystal violet staining and confocal microscopy was used for biofilm and extracellular polymer substance (EPS) inhibition tests. Effects on EPS compounds such as proteins, extracellular DNA, and polysaccharides were also examined. Combined with quantitative real-time PCR of selected agr quorum-sensing systems and biofilm genetic determinants, our complex analysis of vanillin and syringic acid showed similar biofilm and EPS inhibition effects on S. epidermidis strains, reducing biofilm formation up to 80% and EPS up to 55%, depending on the genotype of the tested strain. Natural antimicrobial agents are thus potentially useful inhibitors of biofilms.

Recombinant Enzymatic Redox Systems for Preparation of Aroma Compounds by Biotransformation

The aim of this study was to develop immobilized enzyme systems that reduce carbonyl compounds to their corresponding alcohols. The demand for natural aromas and food additives has been constantly growing in recent years. However, it can no longer be met by extraction and isolation from natural materials. One way to increase the availability of natural aromas is to prepare them by the enzymatic transformation of suitable precursors. Recombinant enzymes are currently being used for this purpose. We investigated trans-2-hexenal bioreduction by recombinant Saccharomyces cerevisiae alcohol dehydrogenase (ScADH1) with simultaneous NADH regeneration by recombinant Candida boidinii formate dehydrogenase (FDH). In a laboratory bioreactor with two immobilized enzymes, 88% of the trans-2-hexenal was transformed to trans-2-hexenol. The initial substrate concentration was 3.7 mM. The aldehyde destabilized ScADH1 by eluting Zn²⁺ ions from the enzyme. A fed-batch operation was used and the trans-2-hexenal concentration was maintained at a low level to limit the negative effect of Zn²⁺ ion elution from the immobilized ScADH1. Another immobilized two-enzyme system was used to reduce acetophenone to (S)-1-phenylethanol. To this end, the recombinant alcohol dehydrogenase (RrADH) from Rhodococcus ruber was used. This biocatalytic system converted 61% of the acetophenone to (S)-1-phenylethanol. The initial substrate concentration was 8.3 mM. All enzymes were immobilized by poly-His tag to Ni²⁺, which formed strong but reversible bonds that enabled carrier reuse after the loss of enzyme activity.

Functional and structural characterisation of 5 missense mutations of the phenylalanine hydroxylase

Phenylketonuria (PKU) and hyperphenylalaninemia (HPA) are a group of genetic disorders predominantly caused by mutations in the phenylalanine hydroxylase (PAH) gene. To date, more than 950 variants have been identified, however the pathogenic mechanism of many variants remains unknown. In this study, in silico prediction and in vitro prokaryotic and eukaryotic expression systems were used to functionally characterize five PAH missense variants (p.F233I, p.R270I, p.F331S, p.S350Y, and p.L358F) previously identified in Slovak and Czech patients. p.F233I, p.R270I, and p.S350Y were classified as deleterious mutations since they showed no specific activity in functional assay and no response to chaperone co-expression. Protein levels of these PAH variants were very low when expressed in HepG2 cells, and only p.S350Y responded to BH4 precursor overload by significant increase in PAH monomer, probably due to reduced rate of protein degradation as the result of proper protein folding. Variants p.F331S and p.L358F exerted residual enzymatic activity in vitro. While the first can be classified as probably pathogenic due to its very low protein levels in HepG2 cells, the latter is considered to be mild mutation with protein levels of approximately 17.85% compared to wt PAH. Our findings contribute to better understanding of structure and function of PAH mutated enzymes and optimal treatment of PKU patients carrying these mutations using BH4 supplementation.

Escherichia coli as a glycoprotein production host: recent developments and challenges

Chinese Hamster Ovary cells are the most popular host expression system for the large-scale production of human therapeutic glycoproteins, but, the race to engineer Escherichia coli to perform glycosylation is gathering pace. The successful functional transfer of an N-glycosylation pathway from Campylobacter jejuni to Escherichia coli in 2002 can be considered as the crucial first engineering step. Here, we discuss the recent advancements in the field of N-glycosylation of recombinant therapeutic proteins in E. coli cells, from the manipulation of glycan composition, to the improvement in glycosylation efficiency, along with the challenges that remain before E. coli can be available as an industry host cell for economically viable glycoprotein production.