Harnessing synthetic biology to enhance heterologous protein expression

Oral Live-Carrier Vaccine of Recombinant Lactococcus lactis Inducing Prophylactic Protective Immunity Against Helicobacter pylori Infection

Helicobacter pylori infects the gastric mucosa and induces chronic gastritis, peptic ulcers, and gastric cancer. Research has demonstrated that vaccination can induce a protective immune response and prevent H. pylori infection. Oral administration of the Lactococcus lactis live-carrier vaccine is safe and easily complied with by the public. In this study, two recombinant L. lactis strains were constructed that expressed antigens of H. pylori urease subunit alpha (UreA) and UreA fused with Escherichia coli heat-labile toxin B subunit (LTB-UreA), named LL-UreA and LL-LTB-UreA, respectively. The expression of antigen proteins was confirmed by Western blotting analysis. Survival assessment indicated that the engineered L. lactis could colonize in the digestive tract of BALB/c mice up to 10 days after the last oral administration with our immunization protocol. The ability to induce immune response and immune protective efficacy of the L. lactis were confirmed. These results indicated that oral administration with LL-UreA or LL-LTB-UreA could induce UreA-specific mucosal secretory IgA (sIgA) and cellular immune response, significantly increasing the cytokines levels of interferon-gamma (IFN-γ), interleukin (IL)-17A, and IL-10, together with the proportion of CD4+IFN-γ+ T cells and CD4+IL17A+ T cells. More importantly, oral administration of LL-UreA and LL-LTB-UreA brought about effective protection in mice to prevent H. pylori infection, especially LL-UreA, resulting in 70% of mice showing no H. pylori colonization and the remaining 30% showing only low levels of colonization. These findings underscore the potential of using orally administered engineered L. lactis vaccines to prevent H. pylori infection.

Chemical Behavior and Bioactive Properties of Spinorphin Conjugated to 5,5'-Dimethyl- and 5,5'-Diphenylhydantoin Analogs

The discovery of new peptides and their derivatives is an outcome of ongoing efforts to identify a peptide with significant biological activity for effective usage as a possible therapeutic agent. Spinorphin peptides have been documented to exhibit numerous applications and features. In this study, biologically active peptide derivatives based on novel peptide analogues of spinorphin conjugated with 5,5'-dimethyl (Dm) and 5,5'-diphenyl (Ph) hydantoin derivatives have been successfully synthesized and characterized. Scanning electron microscopy (SEM) and spectral methods such as UV-Vis, FT-IR (Fourier Transform Infrared Spectroscopy), CD (Circular Dichroism), and fluorimetry were used to characterize the microstructure of the resulting compounds. The results revealed changes in peptide morphology as a result of the restructuring of the aminoacidic sequences and aromatic bonds, which is related to the formation of intermolecular hydrogen bonds between tyrosyl groups and the hydantoin moiety. Electrochemical and fluorescence approaches were used to determine some physicochemical parameters related to the biological behavior of the compounds. The biological properties of the spinorphin derivatives were evaluated in vivo for anticonvulsant activity against the psychomotor seizures at different doses of the studied peptides. Both spinorphin analog peptides with Ph and Dm groups showed activity against all three phases of the seizure in the intravenous Pentylenetetrazole Seizure (ivPTZ) test. This suggests that hydantoin residues do not play a crucial role in the structure of spinorphin compounds and in determining the potency to raise the seizure threshold. On the other hand, analogs with a phenytoin residue are active against the drug-resistant epilepsy test (6-Hz test). In addition, bioactivity analyses revealed that the new peptide analogues have the potential to be used as antimicrobial and antioxidant compounds. These findings suggest promising avenues for further research that may lead to the development of alternative medicines or applications in various fields beyond epilepsy treatment.

Sesquiterpene Synthase Engineering and Targeted Engineering of α-Santalene Overproduction in Escherichia coli

As a natural sesquiterpene compound with numerous biological activities, α-santalene has extensive applications in the cosmetic and pharmaceutical industries. Although several α-santalene-producing microbial strains have been constructed, low productivity still hampers large-scale fermentation. Herein, we present a case of engineered sesquiterpene biosynthesis where the insufficient downstream pathway capacity limited high-level α-santalene production in Escherichia coli. The initial strain was constructed, and it produced 6.4 mg/L α-santalene. To increase α-santalene biosynthesis, we amplified the flux toward farnesyl diphosphate (FPP) precursor by screening and choosing the right FPP synthase and reprogrammed the rate-limiting downstream pathway by generating mutations in santalene synthase (Clausena lansium; ClSS). Santalene synthase was engineered by site-directed mutagenesis, resulting in the improved soluble expression of ClSS and an α-santalene titer of 887.5 mg/L; the α-santalene titer reached 1078.8 mg/L after adding a fusion tag to ClSS. The most productive pathway, which included combining precursor flux amplification and mutant synthases, conferred an approximate 169-fold increase in α-santalene levels. Maximum titers of 1272 and 2916 mg/L were achieved under shake flask and fed-batch fermentation, respectively, and were among the highest levels reported using E. coli as the host.

Design and construction of novel biocatalyst for bioprocessing: Recent advances and future outlook

Bioprocess, a biocatalysis-based technology, is becoming popular in many research fields and widely applied in industrial manufacturing. However, low bioconversion, low productivity, and high costs during industrial processes are usually the limitation in bioprocess. Therefore, many biocatalyst strategies have been developed to meet these challenges in recent years. In this review, we firstly discuss protein engineering strategies, which are emerged for improving the biocatalysis activity of biocatalysts. Then, we summarize metabolic engineering strategies that are promoting the development of microbial cell factories. Next, we illustrate the necessity of using the combining strategy of protein engineering and metabolic engineering for efficient biocatalysts. Lastly, future perspectives about the development and application of novel biocatalyst strategies are discussed. This review provides theoretical guidance for the development of efficient, sustainable, and economical bioprocesses mediated by novel biocatalysts.

Stability of Protein Structure during Nanocarrier Encapsulation: Insights on Solvent Effects from Simulations and Spectroscopic Analysis

The dosing of peptide and protein therapeutics is complicated by rapid clearance from the blood pool and poor cellular membrane permeability. Encapsulation into nanocarriers such as liposomes or polymersomes has long been explored to overcome these limitations, but manufacturing challenges have limited clinical translation by these approaches. Recently, inverse Flash NanoPrecipitation (iFNP) has been developed to produce highly loaded polymeric nanocarriers with the peptide or protein contained within a hydrophilic core, stabilized by a hydrophobic polymer shell. Encapsulation of proteins with higher-order structure requires understanding how processing may affect their conformational state. We demonstrate a combined experimental/simulation approach to characterize protein behavior during iFNP processing steps using the Trp-cage protein TC5b as a model. Explicit-solvent fully atomistic molecular dynamics simulations with enhanced sampling techniques are coupled with two-dimensional heteronuclear multiple-quantum coherence nuclear magnetic resonance spectroscopy (2D-HMQC NMR) and circular dichroism to determine the structure of TC5b during mixed-solvent exposure encountered in iFNP processing. The simulations involve atomistic models of mixed solvents and protein to capture the complexity of the hydrogen bonding and hydrophobic interactions between water, dimethylsulfoxide (DMSO), and the protein. The combined analyses reveal structural unfolding of the protein in 11 M DMSO but confirm complete refolding after release from the polymeric nanocarrier back into an aqueous phase. These results highlight the insights that simulations and NMR provide for the formulation of proteins in nanocarriers.

Stanley E, H. Hecht M. Harnessing synthetic biology to enhance heterologous protein expression

The ability to express heterologous proteins in microbial hosts is crucial for many areas of research and technology. In most cases, however, successful expression and purification of the desired protein require fusion to another protein. To date, all fusion partners have been chosen from natural sequences, which evolved for other purposes, and may not be optimal fusion partners. However, the rise of synthetic biology and protein design make it possible to design and optimize fusion proteins using novel sequences that did not arise in nature. Here, we describe a series of De novo Expression Enhancer Proteins (DEEPs) that facilitate high-level expression and facile purification of heterologous proteins and peptides. To test the DEEP system, a de novo protein was fused to several target proteins covering a range of sizes and solubilities. In all cases, fusions to DEEP outperformed fusions to SUMO, a commonly used natural fusion partner. The availability of novel proteins that can be engineered for specific fusion applications could be beneficial to enhance the expression of a wide range of heterologous proteins.