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- Fleetwood, Filippa, et al.
(author)
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An engineered autotransporter-based surface expression vector enables efficient display of Affibody molecules on OmpT-negative E. coli as well as protease-mediated secretion in OmpT-positive strains
- 2014
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In: Microbial Cell Factories. - : Springer Science and Business Media LLC. - 1475-2859. ; 13, s. 179-
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Journal article (peer-reviewed)abstract
- Background: Cell display technologies (e.g. bacterial display) are attractive in directed evolution as they provide the option to use flow-cytometric cell sorting for selection from combinatorial libraries. The aim of this study was to engineer and investigate an expression vector system with dual functionalities: i) recombinant display of Affibody libraries on Escherichia coli for directed evolution and ii) small scale secreted production of candidate affinity proteins, allowing initial downstream characterizations prior to subcloning. Autotransporters form a class of surface proteins in Gram-negative bacteria that have potential for efficient translocation and tethering of recombinant passenger proteins to the outer membrane. We engineered a bacterial display vector based on the E. coli AIDA-I autotransporter for anchoring to the bacterial surface. Potential advantages of employing autotransporters combined with E. coli as host include: high surface expression level, high transformation frequency, alternative promoter systems available, efficient translocation to the outer membrane and tolerance for large multi-domain passenger proteins. Results: The new vector was designed to comprise an expression cassette encoding for an Affibody molecule, three albumin binding domains for monitoring of surface expression levels, an Outer membrane Protease T (OmpT) recognition site for potential protease-mediated secretion of displayed affinity proteins and a histidine-tag for purification. A panel of vectors with different promoters were generated and evaluated, and suitable cultivation conditions were investigated. The results demonstrated a high surface expression level of the different evaluated Affibody molecules, high correlation between target binding and surface expression level, high signal-to-background ratio, efficient secretion and purification of binders in OmpT-positive hosts as well as tight regulation of surface expression for the titratable promoters. Importantly, a mock selection using FACS from a 1: 100,000 background yielded around 20,000-fold enrichment in a single round and high viability of the isolated bacteria after sorting. Conclusions: The new expression vectors are promising for combinatorial engineering of Affibody molecules and the strategy for small-scale production of soluble recombinant proteins has the potential to increase throughput of the entire discovery process.
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| 2. |
- Fleetwood, Filippa, 1985-
(author)
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Bacterial display systems for engineering of affinity proteins
- 2014
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Doctoral thesis (other academic/artistic)abstract
- Directed evolution is a powerful method for engineering of specific affinity proteins such as antibodies and alternative scaffold proteins. For selections from combinatorial protein libraries, robust and high-throughput selection platforms are needed. An attractive technology for this purpose is cell surface display, offering many advantages, such as the quantitative isolation of high-affinity library members using flow-cytometric cell sorting. This thesis describes the development, evaluation and use of bacterial display technologies for the engineering of affinity proteins.Affinity proteins used in therapeutic and diagnostic applications commonly aim to specifically bind to disease-related drug targets. Angiogenesis, the formation of new blood vessels from pre-existing vasculature, is a critical process in various types of cancer and vascular eye disorders. Vascular Growth Factor Receptor 2 (VEGFR2) is one of the main regulators of angiogenesis. The first two studies presented in this thesis describe the engineering of a biparatopic Affibody molecule targeting VEGFR2, intended for therapeutic and in vivo imaging applications. Monomeric VEGFR2-specific Affibody molecules were generated by combining phage and staphylococcal display technologies, and the engineering of two Affibody molecules, targeting distinct epitopes on VEGFR2 into a biparatopic construct, resulted in a dramatic increase in affinity. The biparatopic construct was able to block the ligand VEGF-A from binding to VEGFR2-expressing cells, resulting in an efficient inhibition of VEGFR2 phosphorylation and angiogenesis-like tube formation in vitro.In the third study, the staphylococcal display system was evaluated for the selection from a single-domain antibody library. This was the first demonstration of successful selection from an antibody-based library on Gram-positive bacteria. A direct comparison to the selection from the same library displayed on phage resulted in different sets of binders, and higher affinities among the clones selected by staphylococcal display. These results highlight the importance of choosing a display system that is suitable for the intended application.The last study describes the development and evaluation of an autotransporter-based display system intended for display of Affibody libraries on E. coli. A dual-purpose expression vector was designed, allowing efficient display of Affibody molecules, as well as small-scale protein production and purification of selected candidates without the need for sub-cloning. The use of E. coli would allow the display of large Affibody libraries due to a high transformation frequency. In combination with the facilitated means for protein production, this system has potential to improve the throughput of the engineering process of Affibody molecules.In summary, this thesis describes the development, evaluation and use of bacterial display systems for engineering of affinity proteins. The results demonstrate great potential of these display systems and the generated affinity proteins for future biotechnological and therapeutic use.
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| 5. |
- Fleetwood, Filippa, et al.
(author)
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Novel affinity binders for neutralization of vascular endothelial growth factor (VEGF) signaling
- 2016
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In: Cellular and Molecular Life Sciences (CMLS). - : Birkhauser Verlag. - 1420-682X .- 1420-9071. ; 73:8, s. 1671-1683
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Journal article (peer-reviewed)abstract
- Angiogenesis denotes the formation of new blood vessels from pre-existing vasculature. Progression of diseases such as cancer and several ophthalmological disorders may be promoted by excess angiogenesis. Novel therapeutics to inhibit angiogenesis and diagnostic tools for monitoring angiogenesis during therapy, hold great potential for improving treatment of such diseases. We have previously generated so-called biparatopic Affibody constructs with high affinity for the vascular endothelial growth factor receptor-2 (VEGFR2), which recognize two non-overlapping epitopes in the ligand-binding site on the receptor. Affibody molecules have previously been demonstrated suitable for imaging purposes. Their small size also makes them attractive for applications where an alternative route of administration is beneficial, such as topical delivery using eye drops. In this study, we show that decreasing linker length between the two Affibody domains resulted in even slower dissociation from the receptor. The new variants of the biparatopic Affibody bound to VEGFR2-expressing cells, blocked VEGFA binding, and inhibited VEGFA-induced signaling of VEGFR2 over expressing cells. Moreover, the biparatopic Affibody inhibited sprout formation of endothelial cells in an in vitro angiogenesis assay with similar potency as the bivalent monoclonal antibody ramucirumab. This study demonstrates that the biparatopic Affibody constructs show promise for future therapeutic as well as in vivo imaging applications.
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| 6. |
- Fleetwood, Filippa, et al.
(author)
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Simultaneous targeting of two ligand-binding sites on VEGFR2 using biparatopic Affibody molecules results in dramatically improved affinity
- 2014
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 4, s. 7518-
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Journal article (peer-reviewed)abstract
- Angiogenesis plays an important role in cancer and ophthalmic disorders such as age-related macular degeneration and diabetic retinopathy. The vascular endothelial growth factor (VEGF) family and corresponding receptors are regulators of angiogenesis and have been much investigated as therapeutic targets. The aim of this work was to generate antagonistic VEGFR2-specific affinity proteins having adjustable pharmacokinetic properties allowing for either therapy or molecular imaging. Two antagonistic Affibody molecules that were cross-reactive for human and murine VEGFR2 were selected by phage and bacterial display. Surprisingly, although both binders independently blocked VEGF-A binding, competition assays revealed interaction with non-overlapping epitopes on the receptor. Biparatopic molecules, comprising the two Affibody domains, were hence engineered to potentially increase affinity even further through avidity. Moreover, an albumin-binding domain was included for half-life extension in future in vivo experiments. The best-performing of the biparatopic constructs demonstrated up to 180-fold slower dissociation than the monomers. The new Affibody constructs were also able to specifically target VEGFR2 on human cells, while simultaneously binding to albumin, as well as inhibit VEGF-induced signaling. In summary, we have generated small antagonistic biparatopic Affibody molecules with high affinity for VEGFR2, which have potential for both future therapeutic and diagnostic purposes in angiogenesis-related diseases.
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| 7. |
- Fleetwood, Filippa, et al.
(author)
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Surface display of a single-domain antibody library on Gram-positive bacteria
- 2013
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In: Cellular and Molecular Life Sciences (CMLS). - : Springer Nature. - 1420-682X .- 1420-9071. ; 70:6, s. 1081-1093
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Journal article (peer-reviewed)abstract
- Combinatorial protein engineering for selection of proteins with novel functions, such as enzymes and affinity reagents, is an important tool in biotechnology, drug discovery, and other biochemical fields. Bacterial display is an emerging technology for isolation of new affinity proteins from such combinatorial libraries. Cells have certain properties that are attractive for directed evolution purposes, in particular the option to use quantitative flow-cytometric cell sorting for selection of binders. Here, an immune library of around 10(7) camelid single-domain antibody fragments (Nanobodies) was displayed on both the Gram-positive bacterium Staphylococcus carnosus and on phage. As demonstrated for the first time, the antibody repertoire was found to be well expressed on the bacterial surface and flow-cytometric sorting yielded a number of Nanobodies with subnanomolar affinity for the target protein, green fluorescent protein (GFP). Interestingly, the staphylococcal output repertoire and the binders from the phage display selection contained two slightly different sets of clones, containing both unique as well as several similar variants. All of the Nanobodies from the staphylococcal selection were also shown to enhance the fluorescence of GFP upon binding, potentially due to the fluorescence-based sorting principle. Our study highlights the impact of the chosen display technology on the variety of selected binders and thus the value of having alternative methods available, and demonstrates in addition that the staphylococcal system is suitable for generation of high-affinity antibody fragments.
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| 8. |
- Leitao, Charles Dahlsson, 1992-, et al.
(author)
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Display of a naïve affibody library on staphylococci for selection of binders by means of flow cytometry sorting
- 2023
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In: Biochemical and Biophysical Research Communications - BBRC. - : Elsevier BV. - 0006-291X .- 1090-2104. ; 655, s. 75-81
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Journal article (peer-reviewed)abstract
- Within the field of combinatorial protein engineering there is a great demand for robust high-throughput selection platforms that allow for unbiased protein library display, affinity-based screening, and amplification of selected clones. We have previously described the development of a staphylococcal display system used for displaying both alternative-scaffolds and antibody-derived pro-teins. In this study, the objective was to generate an improved expression vector for displaying and screening a high-complexity naive affibody library, and to facilitate downstream validation of isolated clones. A high-affinity normalization tag, consisting of two ABD-moieties, was introduced to simplify off-rate screening procedures. In addition, the vector was furnished with a TEV protease substrate recog-nition sequence upstream of the protein library which enables proteolytic processing of the displayed construct for improved binding signal. In the library design, 13 of the 58 surface-exposed amino acid positions were selected for full randomization (except proline and cysteine) using trinucleotide tech-nology. The genetic library was successfully transformed to Staphylococcus carnosus cells, generating a protein library exceeding 109 members. De novo selections against three target proteins (CD14, MAPK9 and the affibody ZEGFR:2377) were successfully performed using magnetic bead-based capture followed by flow-cytometric sorting, yielding affibody molecules binding their respective target with nanomolar affinity. Taken together, the results demonstrate the feasibility of the staphylococcal display system and the proposed selection procedure to generate new affibody molecules with high affinity.
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