Expression of active human P450 3A4 on the cell surface of Escherichia coli by Autodisplay

Stable expression of HIV-1 MPER extended epitope on the surface of the recombinant probiotic bacteria Escherichia Coli Nissle 1917 using CRISPR/Cas9

BACKGROUND

Mucosal vaccines have the potential to induce protective immune responses at the sites of infection. Applying CRISPR/Cas9 editing, we aimed to develop a probiotic-based vaccine candidate expressing the HIV-1 envelope membrane-proximal external region (MPER) on the surface of E. coli Nissle 1917.

RESULTS

The HIV-1 MPER epitope was successfully introduced in the porin OmpF of the E. coli Nissle 1917 (EcN-MPER) and the modification was stable over 30 passages of the recombinant bacteria on the DNA and protein level. Furthermore, the introduced epitope was recognized by a human anti-HIV-1 gp41 (2F5) antibody using both live and heat-killed EcN-MPER, and this antigenicity was also retained over 30 passages. Whole-cell dot blot suggested a stronger binding of anti-HIV-1 gp41 (2F5) to heat-killed EcN-MPER than their live counterpart. An outer membrane vesicle (OMV) - rich extract from EcN-MPER culture supernatant was equally antigenic to anti-HIV-1 gp41 antibody which suggests that the MPER antigen could be harboured in EcN-MPER OMVs. Using quantitative ELISA, we determined the amount of MPER produced by the modified EcN to be 14.3 µg/108 cfu.

CONCLUSIONS

The CRISPR/Cas9 technology was an effective method for establishment of recombinant EcN-MPER bacteria that was stable over many passages. The developed EcN-MPER clone was devoid of extraneous plasmids and antibiotic resistance genes which eliminates the risk of plasmid transfer to animal hosts, should this clone be used as a vaccine. Also, the EcN-MPER clone was recognised by anti-HIV-1 gp41 (2F5) both as live and heat-killed bacteria making it suitable for pre-clinical evaluation. Expression of OmpF on bacterial surfaces and released OMVs identifies it as a compelling candidate for recombinant epitope modification, enabling surface epitope presentation on both bacteria and OMVs. By applying the methods described in this study, we present a potential platform for cost-effective and rational vaccine antigen expression and administration, offering promising prospects for further research in the field of vaccine development.

Autodisplay of streptococcal protein G for construction of an orientation-controlled immunoaffinity layer

An immunoaffinity layer with orientation-controlled antibodies was constructed to express streptococcal protein G in Escherichia coli cells using autodisplay technology. The sequence of protein G, a specific IgG-binding protein, was inserted into the autodisplay vector using recombinant technology and the constructed plasmid vector was transformed into E. coli cells. Protein G was confirmed to be autodisplayed with a high density of 2 × 10⁵ copies per cell by SDS-PAGE analysis, and its IgG-binding affinity was confirmed by fluorescence microscopy. Autodisplayed protein G showed higher affinity than the IgG-binding Z-domain for goat IgG. Immunoassays based on E. coli cells were established to detect horseradish peroxidase (HRP) and C-reactive protein (CRP). Protein G autodisplaying E. coli cells were utilized as a solid support and immunoassays showed improved sensitivity by orientation control of autodisplayed protein G. The outer membrane (OM) of protein G autodisplaying E. coli was isolated and layered to construct an immunoaffinity layer. The OM was coated on a microplate to perform the immunoassays, which showed limits of detection of 5 and 0.2 ng mL^-1 for HRP and CRP, respectively. An OM layer with autodisplayed protein G was applied as the immunoaffinity layer of a surface plasmon resonance (SPR) biosensor. After CRP detection, the SPR responses showed good linearity, with an R² value of 0.99. The immunoaffinity layer with orientation control by autodisplayed protein G was confirmed to be applicable in immunoassays and immunosensors to improve sensitivity.

Autodisplay of human PIP5K1α lipid kinase on Escherichia coli and inhibitor testing

The human phosphatidylinositol 4-phosphate 5-kinase type I α (hPIP5K1α) plays a major role in the PI3K/AKT/mTOR signaling pathway. As it has been shown before that hPIP5K1α is involved in the development of different types of cancer in particular prostate cancer, inhibitors of the enzyme might be a new option for the treatment of this disease. Here we report on the expression of hPIP5K1α on the surface of E. coli using Autodisplay. Autodisplay is defined as the surface display of a recombinant protein on a gramnegative bacterium by the autotransporter secretion pathway. After verification of surface expression, enzyme activity of whole cells displaying hPIP5K1α was determined by a capillary electrophoresis based assay. When using cells at an OD₅₇₈ of 2.5, the artificial substrate phosphatidylinositol4-phosphate (PI(4)P) fluorescein was converted by a rate of 10.7 ± 0.2 fmol/min. Using this substrate inhibition of three pyranobenzoquinone type compounds was tested. The most active compound was 4-(2-amino-3-cyano-6-hydroxy-5,8-dioxo-7-undecyl-5,8-dihydro-4H-chromen-4-yl) benzoic acid with an IC₅₀ value of 8.6 μM. Because until now, all attempts to purify hPIP5K1α failed, we suggest the use of whole cells of E. coli displaying the enzyme as a convenient tool for inhibitor identification.

Combining Cell Surface Display and DNA-Shuffling Technology for Directed Evolution of Streptomyces Phospholipase D and Synthesis of Phosphatidylserine

Phospholipids have been widely used in food, medicine, cosmetics, and other fields because of their unique chemical structure and healthcare functions. Phospholipase D (PLD) is a key biocatalyst for the biotransformation of phospholipids. Here, an autodisplay expression system was constructed for rapid screening of mutants, and PLD variants were recombined using DNA shuffling technology and three beneficial mutations were obtained. The results of enzymatic performance and sequence information comparison indicated that C-terminal amino acids exerted a greater impact on the correct folding of PLDs, and N-terminal amino acids are more important for catalytic reaction. The best-performing recombinant enzyme in transphosphatidylation reactions was Recom-34, with a phosphatidylserine content accounting for 80.3% of total phospholipids and a 3.24-fold increased conversion rate compared to the parent enzyme. This study demonstrates great significance for screening ideal biocatalysts, facilitating soluble expression of inclusion body proteins, and identifying key amino acids.

Functional Surface Display of Laccase in a Phenol-Inducible Bacterial Circuit for Bioremediation Purposes

Background:

Phenolic compounds, which are produced routinely by industrial and urban activities, possess dangers to live organisms and environment. Laccases are oxidoreductase enzymes with the ability of remediating a wide variety of phenolic compounds to more benign molecules. The purpose of the present research is surface display of a laccase enzyme with adhesin involved in diffuse adhesion (AIDA-I) autotransporter system on the surface of Escherichia coli cells for bioremediation of phenolic compounds.

Methods:

The expression of laccase was regulated by a phenol-responsive promoter (a σ⁵⁴promoter). The constitutively-expressed CapR transcription activator was able to induce laccase expression in the presence of phenolic compounds.

Results:

Western blot analysis showed the expression and correct transfer of the enzyme to the outer membrane of E. coli cells in the presence of phenol. Activity assay confirmed the correct folding of the enzyme after translocation through the autotransporter system. HPLC analysis of residual phenol in culture medium showed a significant reduction of phenol concentration in the presence of cells displaying laccase on the surface.

Conclusion:

Our findings confirm that autodisplay enables functional surface display of laccase for direct substrate-enzyme availability by overcoming membrane hindrance.

Autodisplay of glucose-6-phosphate dehydrogenase for redox cofactor regeneration at the cell surface

Inherent cofactor regeneration is a pivotal feature of whole cell biocatalysis. For specific biotechnological applications, surface display of enzymes is emerging as a tool to circumvent mass transfer limitations or enzyme stability problems. Even complex reactions can be accomplished applying displayed enzymes. Yet, industrial utilization of the technique is still impeded by lacking cofactor regeneration at the cell surface. Here, we report on the surface display of a glucose-6-phoshate dehydrogenase (G6PDH) via Autodisplay to address this limitation and regenerate NADPH directly at the cell surface. The obtained whole cell biocatalyst demonstrated similar kinetic parameters compared to the purified enzyme, more precisely K_M values of 0.2 mM for NADP⁺ and calculated total turnover numbers of 10⁷ . However, the K_M for the substrate G6P increased by a factor of 7 to yield 1.5 mM. The whole cell biocatalyst was cheaper to produce, easy to separate from the reaction mixture and reusable in consecutive reaction cycles. Furthermore, lyophilization allowed storage at room temperature. The whole cell biocatalyst displaying G6PDH was applicable for NADPH regeneration in combination with soluble as well as surface displayed enzymes and model reactions in combination with bacterial CYP102A1 and human CYP1A2 were realized. Biotechnol. Bioeng. 2017;114: 1658-1669. © 2017 Wiley Periodicals, Inc.

Differential protein expression and localization of CYP450 enzymes in three species of earthworm; is this a reflection of environmental adaptation?

Cytochrome P450 (CYP450) is a hemoprotein superfamily, among which CYP1, CYP2 and CYP3 play a major role in the metabolism of vast array of xenobiotics and endobiotics. This paper reports on three CYP enzyme variants (CYP1A2, CYP2E1 and CYP3A4) in three species of earthworm (Eisenia fetida, Metaphire guillelmi and Amynthas carnosus). The relative expression levels and localization of the three associated proteins were investigated at three life-cycle points (juvenile, sub-adult and adult), through comparison of anterior and posterior body tissue and between specific organs (body wall, intestine and reproductive tissues) using western blot analysis. This study confirmed the presence of CYP3A4, CYP1A2 and CYP2E1 in all three species of earthworm tested. The levels of expression varied with earthworm species, age, and body location. These differences in occurrence of the three CYP enzymes appeared to reflect the ecological niche (the spatial and temporal location and functional relationship of each individual or population in populations or communities), and the likelihood of contact with soil contaminants of the respective species. These results may help to explain why earthworms are capable of adapting to very different and extensively polluted soil environments and provide important data for subsequent ecotoxicology and ecological adaptability studies.

A magnetite suspension-based washing method for immunoassays using Escherichia coli cells with autodisplayed Z-domains

Escherichia coli cells with autodisplayed Z-domains have been used for immunoassays of specific target analytes. In this study, a magnetite suspension was used for the washing step in immunoassays of E. coli cells with autodisplayed Z-domains. This approach enhanced the washing conditions for these immunoassays by determining (1) the optimal concentration of the magnetite suspension, (2) the capacity of the magnetite suspension-based washing method to recover E. coli cells, and (3) the level at which the activity of autodisplayed Z-domains is maintained. In immunoassays of C-reactive protein (CRP), the immunoassay incorporating the magnetite suspension-based washing method showed a sensitivity and limit of detection considerably higher than those of the conventional centrifugation-based washing method. The results indicated that immunoassays incorporating the magnetite suspension-based washing method are effective for medical diagnoses based on CRP assay.

Application of nanodisc technology for direct electrochemical investigation of plant cytochrome P450s and their NADPH P450 oxidoreductase

Direct electrochemistry of cytochrome P450 containing systems has primarily focused on investigating enzymes from microbes and animals for bio-sensing applications. Plant P450s receive electrons from NADPH P450 oxidoreductase (POR) to orchestrate the bio-synthesis of a plethora of commercially valuable compounds. In this report, full length CYP79A1, CYP71E1 and POR of the dhurrin pathway in Sorghum bicolor were reconstituted individually in nanoscale lipid patches, "nanodiscs", and directly immobilized on unmodified gold electrodes. Cyclic voltammograms of CYP79A1 and CYP71E1 revealed reversible redox peaks with average midpoint potentials of 80 ± 5 mV and 72 ± 5 mV vs. Ag/AgCl, respectively. POR yielded two pairs of redox peaks with midpoint potentials of 90 ± 5 mV and -300 ± 10 mV, respectively. The average heterogeneous electron transfer rate constant was calculated to be ~1.5 s(-1). POR was electro-catalytically active while the P450s generated hydrogen peroxide (H2O2). These nanodisc-based investigations lay the prospects and guidelines for construction of a simplified platform to perform mediator-free, direct electrochemistry of non-engineered cytochromes P450 under native-like conditions. It is also a prelude for driving plant P450 systems electronically for simplified and cost-effective screening of potential substrates/inhibitors and fabrication of nano-bioreactors for synthesis of high value natural products.

Co-expression of active human cytochrome P450 1A2 and cytochrome P450 reductase on the cell surface of Escherichia coli

Background

Human cytochrome P450 (CYP) enzymes mediate the first step in the breakdown of most drugs and are strongly involved in drug–drug interactions, drug clearance and activation of prodrugs. Their biocatalytic behavior is a key parameter during drug development which requires preparative synthesis of CYP related drug metabolites. However, recombinant expression of CYP enzymes is a challenging bottleneck for drug metabolite biosynthesis. Therefore, we developed a novel approach by displaying human cytochrome P450 1A2 (CYP1A2) and cytochrome P450 reductase (CPR) on the surface of Escherichia coli.

Results

To present human CYP1A2 and CPR on the surface, we employed autodisplay. Both enzymes were displayed on the surface which was demonstrated by protease and antibody accessibility tests. CPR activity was first confirmed with the protein substrate cytochrome c. Cells co-expressing CYP1A2 and CPR were capable of catalyzing the conversion of the known CYP1A2 substrates 7-ethoxyresorufin, phenacetin and the artificial substrate luciferin-MultiCYP, which would not have been possible without interaction of both enzymes. Biocatalytic activity was strongly influenced by the composition of the growth medium. Addition of 5-aminolevulinic acid was necessary to obtain a fully active whole cell biocatalyst and was superior to the addition of heme.

Conclusion

We demonstrated that CYP1A2 and CPR can be co-expressed catalytically active on the cell surface of E. coli. It is a promising step towards pharmaceutical applications such as the synthesis of drug metabolites.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0427-5) contains supplementary material, which is available to authorized users.

A simplified process design for P450 driven hydroxylation based on surface displayed enzymes

New production routes for fine and bulk chemicals are important to establish further sustainable processes in industry. Besides the identification of new biocatalysts and new production routes the optimization of existing processes in regard to an improved utilization of the catalysts are needed. In this paper we describe the successful expression of P450BM3 on the surface of E. coli cells with the Autodisplay system. The successful hydroxylation of palmitic acid by using surface-displayed P450BM3 was shown. Besides optimization of surface protein expression, several cofactor regeneration systems were compared and evaluated. Afterwards, the development of a suitable process for the biocatalytic hydroxylation of fatty acids based on the re-use of the catalysts after a simple centrifugation was investigated. It was shown that the catalyst can be used for several times without any loss in activity. By using surface-displayed P450s in combination with an enzymatic cofactor regeneration system a total turnover number of up to 54,700 could be reached, to the knowledge of the authors the highest value reported for a P450 monooxygenase to date. Further optimizations of the described reaction system can have an enormous impact on the process design for more sustainable bioprocesses. Biotechnol. Bioeng. 2016;113: 1225-1233. © 2015 Wiley Periodicals, Inc.

Extracellular protease digestion to evaluate membrane protein cell surface localization

Membrane proteins have crucial roles in signaling and as anchors for cell surface display. Proper secretion of a membrane protein can be evaluated by its susceptibility to digestion by an extracellular protease, but this requires a crucial control to confirm membrane integrity during digestion. This protocol describes how to use this approach to determine how efficiently a protein is secreted to the outer surface of Gram-negative bacteria. Its success relies upon careful selection of an appropriate intracellular reporter protein that will remain undigested if the membrane barrier remains intact, but that is rapidly digested when cells are lysed before evaluation. Reporter proteins that are resistant to proteases (e.g., maltose-binding protein) do not return accurate results; in contrast, proteins that are more readily digested (e.g., SurA) serve as more sensitive reporters of membrane integrity, yielding more accurate measurements of membrane protein localization. Similar considerations apply when evaluating membrane protein localization in other contexts, including eukaryotic cells and organelle membranes. Evaluating membrane protein localization using this approach requires only standard biochemistry laboratory equipment for cell lysis, gel electrophoresis and western blotting. After expression of the protein of interest, this procedure can be completed in 4 h.

Autodisplay of Human Hyaluronidase Hyal-1 on Escherichia coli and Identification of Plant-Derived Enzyme Inhibitors

Hyaluronan (HA) is the main component of the extracellular matrix (ECM). Depending on its chain size, it is generally accepted to exert diverse effects. High molecular weight HA is anti-angiogenic, immunosuppressive and anti-inflammatory, while lower fragments are angiogenic and inflammatory. Human hyaluronidase Hyal-1 (Hyal-1) is one of the main enzymes in the metabolism of HA. This makes Hyal-1 an interesting target. Not only for functional and mechanistic studies, but also for drug development. In this work, Hyal-1 was expressed on the surface of E. coli, by applying Autodisplay, to overcome formation of inactive “inclusion bodies”. With the cells displaying Hyal-1 an activity assay was performed using “stains-all” dye. Subsequently, the inhibitory effects of four saponins and 14 plant extracts on the activity of surface displayed Hyal-1 were evaluated. The determined IC₅₀ values were 177 µM for glycyrrhizic acid, 108 µM for gypsophila saponin 2, 371 µM for SA1657 and 296 µM for SA1641. Malvae sylvestris flos, Equiseti herba and Ononidis radix extracts showed IC₅₀ values between 1.4 and 1.7 mg/mL. In summary, Autodisplay enabled the expression of functional human target protein Hyal-1 in E. coli and facilitated an accelerated testing of potential inhibitors.

Functional display of heterotetrameric human protein kinase CK2 on Escherichia coli: a novel tool for drug discovery

Background

Human protein kinase CK2 represents a novel therapeutic target for neoplastic diseases. Inhibitors are in need to explore the druggability and the therapeutic options of this enzyme. A bottleneck in the search for new inhibitors is the availability of the target for testing. Therefore an assay was developed to provide easy access to CK2 for discovery of novel inhibitors.

Results

Autodisplay was used to present human CK2 on the surface of Escherichia coli. Heterotetrameric CK2 consists of two subunits, α and β, which were displayed individually on the surface. Co-display of CK2α and CK2β on the cell surface led to the formation of functional holoenzyme, as demonstrated by NaCl dependency of enzymatic activity, which differs from that of the catalytic subunit CK2α without β. In addition interaction of CK2α and CK2β at the cell surface was confirmed by co-immunoprecipitation assays. Surface displayed CK2 holoenzyme enabled an easy IC₅₀ value determination. The IC₅₀ values for the known CK2 inhibitors TBB and Silmitasertib were determined to be 50 and 3.3 nM, respectively.

Conclusion

Surface-displayed CK2α and CK2β assembled on the cell surface of E. coli to an active tetrameric holoenzyme. The whole-cell CK2 autodisplay assay as developed is suitable for inhibition studies. Furthermore, it can be used to determine quantitative CK2 inhibition data such as IC₅₀ values. In summary, this is the first report on the functional surface display of a heterotetrameric enzyme on E. coli.

Electrochemical analysis of autodisplayed adrenodoxin (Adx) on the outer membrane of E. coli

In this work, adrenodoxin (Adx) was expressed on the outer membrane of E. coli by autodisplay and then the iron-sulfur cluster was incorporated into apo-Adx by an anaerobic reconstitution process. For the determination of the redox potentials of the iron-sulfur clusters of the autodisplayed Adx, E. coli cells with autodisplayed Adx were immobilized on a gold electrode modified with a self-assembled monolayer of mercaptoundecanoic acid (MUA). From the repeated cyclic voltammetry (CV) analysis, the E. coli (10mM HEPES buffer, pH7.0) with autodisplayed Adx showed significant changes in shape with an oxidation peak at +0.4V (vs. Ag/AgCl) and a reduction peak at -0.3V (vs. Ag/AgCl) after the reconstitution process for the incorporation of the iron-sulfur cluster. From the repeated CV analysis in the reduction and oxidation potential ranges, the iron-sulfur clusters of the autodisplayed Adx were observed to undergo reversible redox reactions via direct electron transfer to the MUA-modified gold electrode.

Guidelines for development and implementation of biocatalytic P450 processes

Biocatalytic reactions performed by cytochrome P450 monooxygenases are interesting in pharmaceutical research since they are involved in human drug metabolism. Furthermore, they are potentially interesting as biocatalysts for synthetic chemistry because of the exquisite selectivity of the chemistry they undertake. For example, selective hydroxylation can be undertaken on a highly functionalized molecule without the need for functional group protection. Recent progress in the discovery of novel P450s as well as protein engineering of these enzymes strongly encourages further development of their application, including use in synthetic processes. The biological characteristics of P450s (e.g., cofactor dependence) motivate the use of whole-cell systems for synthetic processes, and those processes implemented in industry are so far dominated by growing cells and native host systems. However, for an economically feasible process, the expression of P450 systems in a heterologous host with sufficient biocatalyst yield (g/g cdw) for non-growing systems or space-time yield (g/L/h) for growing systems remains a major challenge. This review summarizes the opportunities to improve P450 whole-cell processes and strategies in order to apply and implement them in industrial processes, both from a biological and process perspective. Indeed, a combined approach of host selection and cell engineering, integrated with process engineering, is suggested as the most effective route to implementation.

Autodisplay of an archaeal γ-lactamase on the cell surface of Escherichia coli using Xcc_Est as an anchoring scaffold and its application for preparation of the enantiopure antiviral drug intermediate (-) vince lactam

At present, autotransporter protein mediated surface display has opened a new dimension in the development of whole-cell biocatalysts. Here, we report the identification of a novel autotransporter Xcc_Est from Xanthomonas campestris pv campestris 8004 by bioinformatic analysis and application of Xcc_Est as an anchoring motif for surface display of γ-lactamase (Gla) from thermophilic archaeon Sulfolobus solfataricus P2 in Escherichia coli. The localization of γ-lactamase in the cell envelope was monitored by Western blot, activity assay and flow cytometry analysis. Either the full-length or truncated Xcc_Est could efficiently transport γ-lactamase to the cell surface. Compared with the free enzyme, the displayed γ-lactamase exhibited optimum temperature of 30 °C other than 90 °C, with a substantial decrease of 60 °C. Under the preparation system, the engineered E. coli with autodisplayed γ-lactamase converted 100 g racemic vince lactam to produce 49.2 g (-) vince lactam at 30 °C within 4 h. By using chiral HPLC, the ee value of the produced (-) vince lactam was determined to be 99.5 %. The whole-cell biocatalyst exhibited excellent stability under the operational conditions. Our results indicate that the E. coli with surface displayed γ-lactamase is an efficient and economical whole cell biocatalyst for preparing the antiviral drug intermediate (-) vince lactam at mild temperature, eliminating expensive energy cost performed at high temperature.

Autodisplay for the co-expression of lipase and foldase on the surface of E. coli: washing with designer bugs

BACKGROUND

Lipases including the lipase from Burkholderia cepacia are in a main focus in biotechnology research since many years because of their manifold possibilities for application in industrial processes. The application of Burkholderia cepacia lipase for these processes appears complicated because of the need for support by a chaperone, the lipase specific foldase. Purification and reconstitution protocols therefore interfere with an economic implementation of such enzymes in industry. Autodisplay is a convenient method to express a variety of passenger proteins on the surface of E. coli. This method makes subsequent purification steps to obtain the protein of interest unnecessary. If enzymes are used as passengers, the corresponding cells can simply be applied as whole cell biocatalysts. Furthermore, enzymes surface displayed in this manner often acquire stabilization by anchoring within the outer membrane of E. coli.

RESULTS

The lipase and its chaperone foldase from B. cepacia were co-expressed on the surface of E. coli via autodisplay. The whole cell biocatalyst obtained thereby exhibited an enzymatic activity of 2.73 mU mL⁻¹ towards the substrate p-nitrophenyl palmitate when applied in an OD₅₇₈ =1. Outer membrane fractions prepared from the same culture volume showed a lipase activity of 4.01 mU mL⁻¹. The lipase-whole cell biocatalyst as well as outer membrane preparations thereof were used in a standardized laundry test, usually adopted to determine the power of washing agents. In this test, the lipase whole cell biocatalyst and the membrane preparation derived thereof exhibited the same lipolytic activity as the purified lipase from B. cepacia and a lipase preparation which is already applied in commercial washing agents.

CONCLUSIONS

Co-expression of both the lipase and its chaperone foldase on the surface of E. coli yields a lipid degrading whole cell biocatalyst. Therefore the chaperone supported folding process, absolutely required for the lipolytic activity appears not to be hindered by surface display. Furthermore, the cells and the membrane preparations appeared to be stable enough to endure a European standard laundry test and show efficient fat removal properties herein.

Preparation of sticky Escherichia coli through surface display of an adhesive catecholamine moiety

Mussels attach to virtually all types of inorganic and organic surfaces in aqueous environments, and catecholamines composed of 3,4-dihydroxy-l-phenylalanine (DOPA), lysine, and histidine in mussel adhesive proteins play a key role in the robust adhesion. DOPA is an unusual catecholic amino acid, and its side chain is called catechol. In this study, we displayed the adhesive moiety of DOPA-histidine on Escherichia coli surfaces using outer membrane protein W as an anchoring motif for the first time. Localization of catecholamines on the cell surface was confirmed by Western blot and immunofluorescence microscopy. Furthermore, cell-to-cell cohesion (i.e., cellular aggregation) induced by the displayed catecholamine and synthesis of gold nanoparticles on the cell surface support functional display of adhesive catecholamines. The engineered E. coli exhibited significant adhesion onto various material surfaces, including silica and glass microparticles, gold, titanium, silicon, poly(ethylene terephthalate), poly(urethane), and poly(dimethylsiloxane). The uniqueness of this approach utilizing the engineered sticky E. coli is that no chemistry for cell attachment are necessary, and the ability of spontaneous E. coli attachment allows one to immobilize the cells on challenging material surfaces such as synthetic polymers. Therefore, we envision that mussel-inspired catecholamine yielded sticky E. coli that can be used as a new type of engineered microbe for various emerging fields, such as whole living cell attachment on versatile material surfaces, cell-to-cell communication systems, and many others.

Autotransporter-based cell surface display in Gram-negative bacteria

Cell surface display of proteins can be used for several biotechnological applications such as the screening of protein libraries, whole cell biocatalysis and live vaccine development. Amongst all secretion systems and surface appendages of Gram-negative bacteria, the autotransporter secretion pathway holds great potential for surface display because of its modular structure and apparent simplicity. Autotransporters are polypeptides made up of an N-terminal signal peptide, a secreted or surface-displayed passenger domain and a membrane-anchored C-terminal translocation unit. Genetic replacement of the passenger domain allows for the surface display of heterologous passengers. An autotransporter-based surface expression module essentially consists of an application-dependent promoter system, a signal peptide, a passenger domain of interest and the autotransporter translocation unit. The passenger domain needs to be compatible with surface translocation although till now no general rules have been determined to test this compatibility. The autotransporter technology for surface display of heterologous passenger domains is critically discussed for various applications.

Autodisplay of functional CYP106A2 in Escherichia coli

Cytochrome P450 enzymes catalyse a wide variety of reactions, including the hydroxylation and epoxidation of CC bonds, and dealkylation reactions. There is high interest in these reactions for biotechnology and pharmaceutical processes. Many P450s require membrane surroundings and have substrates that do not cross biological membranes. To circumvent these obstacles, CYP106A2 from Bacillus megaterium was expressed on the outer membrane of Escherichia coli cells by Autodisplay. Exposure on the surface was confirmed by a protease accessibility test and flow cytometry after immunolabelling. HPLC assays showed that 0.5 ml of cells displaying the enzyme (OD₅₇₈ = 6) converted 9.13 μmol of deoxycorticosterone to 15β-OH-deoxycorticosterone within 1h. Imipramine and abietic acid were also accepted as substrates. The number of active enzyme molecules per cell was calculated to be 20,000. Surprisingly, surface-exposed CYP106A2 was active in E. coli BL21 without the external addition of the heme group. However, when CYP106A2 was expressed on the surface of an E. coli strain lacking the TolC channel protein (JW5503), enzymatic activity was almost completely abolished. The activity of CYP106A2 on the surface of E. coli JW5503 could be restored by the external addition of the heme group. This suggests, as has been reported before, that E. coli uses a TolC-dependent mechanism to export heme into the growth media, where it can be scavenged by a surface-displayed apoenzyme. Our results indicate that Autodisplay enables the functional surface display of P450 enzymes and provides a new platform to access their synthetic potential.