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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
KTH, School of Biotechnology (BIO), Protein Technology.
KTH, School of Biotechnology (BIO), Protein Technology.
KTH, School of Biotechnology (BIO), Protein Technology.ORCID iD: 0000-0002-9282-0174
KTH, School of Biotechnology (BIO), Protein Technology.ORCID iD: 0000-0001-9423-0541
2014 (English)In: Microbial Cell Factories, ISSN 1475-2859, Vol. 13, 179- p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2014. Vol. 13, 179- p.
Keyword [en]
Affibody molecule, Bacterial display, Directed evolution, Combinatorial protein engineering, AIDA-I, Autotransporter, FACS, Secreted protein production, E. coli, Phage display
National Category
Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
URN: urn:nbn:se:kth:diva-156531DOI: 10.1186/s12934-014-0179-zISI: 000349043900001ScopusID: 2-s2.0-84924087937OAI: diva2:767027
Swedish Research Council, 621-2012-5336

QC 20150303

Available from: 2014-11-28 Created: 2014-11-28 Last updated: 2015-03-03Bibliographically approved
In thesis
1. Bacterial display systems for engineering of affinity proteins
Open this publication in new window or tab >>Bacterial display systems for engineering of affinity proteins
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. 89 p.
TRITA-BIO-Report, ISSN 1654-2312 ; 2014:18
Combinatorial protein engineering, staphylococcal display, Affibody, biparatopic, VEGFR2, nanobody, E. coli display, autotransporter
National Category
Engineering and Technology
Research subject
urn:nbn:se:kth:diva-156420 (URN)978-91-7595-374-8 (ISBN)
Public defence
2014-12-19, FD5, AlbaNova Universitetscentrum, KTH, Stockholm, 10:00 (English)
Swedish Research CouncilVinnovaSwedish Foundation for Strategic Research

QC 20141203

Available from: 2014-12-03 Created: 2014-11-28 Last updated: 2014-12-03Bibliographically approved

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