L’ingénierie protéique servant autrefois à comprendre les relations structures-fonctions des protéines connait un tournant majeur depuis plusieurs années. L’ingénierie protéique évolue pour créer des nouvelles fonctions protéiques : c’est la naissance de l’ingénierie protéique moderne. L’objectif de ma thèse a consisté à mettre en place et caractériser deux approches indépendantes d’ingénierie protéique dans le domaine du vaccin et du diagnostic. Le premier projet consistait à générer des ligands protéiques à partir d‘échafaudages moléculaires (des alternatifs aux anticorps) en couplant le ribosome display au NGS et en développant des outils d’analyses bio-informatiques. Des sélections contre des cibles protéiques d’origine bactérienne et virale ont conduit à l’identification de ligands Affibodies affins (µM au nM). Leur caractérisation a validé leur potentiel comme outil de recherche et de réactif diagnostique. Ces études ont permis de valider la plateforme de génération des ligands mise en place, en augmentant l’exploration de l’espace de diversité des interactions des ligands. Le second projet portait sur le développement d’une plateforme de présentation et de vectorisation à partir de particules d’encapsuline. Elles ont été génétiquement modifiées pour présenter de manière répétée à leur surface l’ectodomaine de la protéine de matrice M2 (M2e) du virus Influenza A H1N1 tout en encapsulant une protéine hétérologue : l’eGFP. Les nanoparticules modifiées sont correctement formées et encapsulent l’eGFP. Des souris immunisées par ces particules induisent une réponse anticorps spécifique contre l’épitope M2e et l’eGFP. L’utilisation de ces nanoparticules comme plateforme vaccinale de présentation et de vectorisation est prometteuse et ouvre la voie pour d’autres applications en biotechnologie / In the past, protein engineering used to understand function and structure relationship. But since few years, protein engineering was used to create new protein functions: modern protein engineering was born. The aim of my thesis was to set up and characterize two approaches of protein engineering in diagnostic and vaccine field. The first project was to generate artificial binder using protein scaffolds as an alternative to antibodies by coupling ribosome display (RD) to NGS and developing bio-informatics tools. Screening and selection against bacterial and viral targets have led to affibody binder’s identification with an affinity range from µM to nM. Their characterization has validated their potential as research tools and protein reagents for diagnostic assay. Coupling ribosome display to high throughput sequencing as means to directly identify selected binder coding sequences, enormously enhance binder discovery depth. The second project was to generate an innovative nanocarrier based on encapsulin nanoparticle, for customized peptide display and cargo protein vectorization. Encapsulin particles from T.maritima were genetically modified for simultaneous display of the matrix protein 2 ectodomain of the influenza H1N1 A virus and heterologous protein eGFP packaging. Genetically engineered encapsulin nanoparticles were well-formed and abled to efficiently load eGFP. Immunogenicity studies revealed antibody responses against both the surface epitope and the loaded cargo protein. Taken together, this display system is a versatile tool for rational vaccine design and paves the way for new applications in the research fields of vaccine, antimicrobial research and other biotechnological applications

The rapid development of the gene engineering techniques, especially methods for in vitro directed evolution and combinatorial mutagenesis, has triggered the generation of new binding agents to almost any antigen of interest as an alternative to broadly used antibodies. These so-called non-Ig scaffolds are often derived from proteins with useful biophysical properties. While the therapeutic market is still dominated by monoclonal antibodies, the easy option of desired customization of non-Ig binders by conventional methods of gene engineering predestine them largely for the use in the diagnostic area. The ABD scaffold, derived from a three-helix bundle of albumin-binding domain of streptococcal protein G, represents one of the small non-Ig scaffolds. In our laboratory, we have established a highly complex combinatorial library developed on the ABD scaffold. This ABD scaffold-derived library was used to generate unique binders of human prostate cancer (PCa) biomarkers PSP94, KLK2, KLK11 for the more precise diagnosis of PCa. The second part of the thesis describes the generation of ABD-derived binders selectively recognizing different phenotypes of circulating tumor cells as a binding component of the cell capture zone of microfluidic chip for lung adenocarcinoma diagnosis. Beside this already...

Fast and precise quantification of circulating tumour cells (CTC) in lung adenocarcinoma is a pivotal step in acceleration of diagnosis, selection of early therapy and estimation of treatment prognosis. Development of a new type of microfluidic device based on detection and quantification of epithelial- and mesenchymal-type CTC by high-affinity and cell-type specific protein binders anchored to a microfluidic chip surface represents a highly innovative approach. In this work, we used EpCAM membrane glycoprotein as a target for generation of epithelial cell-specific protein binders by a directed evolution of proteins selected from highly complex combinatorial libraries derived from albumin-binding domain scaffold (ABD) or human muscle protein domain-derived "Myomedin" scaffold. Collections of EpCAM-binding candidates from the both used libraries were generated and particular binding variants were further characterized by DNA sequencing, biochemically and by functional cell-surface binding assays. The best candidates might serve as robust anchor proteins of a microfludic chip. Key words: epithelial cell, EpCAM, protein binder, ribosome display, combinatorial library, protein scaffold

Affinity proteins are invaluable tools in biotechnological and medical applications. This thesis is about combinatorial protein engineering principles for the generation of novel affinity proteins to purify mouse immunoglobulin, detect a potential cancer marker protein or inhibit a cell proliferation pathway. In a first study, ribosome display was for the first time applied to the selection of so-called affibody molecules, including the design of a ribosome display gene cassette, initial test enrichment experiments and the selection of binders against murine IgG1. One of the selected binders (ZMAB25) showed a highly selective binding profile to murine IgG1, which was exploited in the recovery of two different mouse monoclonal IgG1 antibodies from a bovine immunoglobulin-containing background. Ribosome display was further applied to the selection of affibody molecules binding to SATB1, a suggested marker protein for metastasizing adenocarcinoma. The study also included the selection of VHH antibody fragments from a naïve gene repertoire displayed on phage. Binders from both classes of protein scaffolds could be isolated that selectively recognized SATB1 but not its close homologue SATB2, and were used to detect endogenous SATB1 in Jurkat cells by immunofluorescence microscopy. The well-established phage display technology was used to select affibody molecules binding to H-Ras and Raf-1, both involved in the mitogen-activated protein kinase (MAPK) pathway and playing a central role in the control of cell proliferation, survival and differentiation. An isolated affibody molecule denoted ZRAF322 was found to selectively bind to Raf-1 and inhibit the interaction between H-Ras and Raf-1 in vitro. In a continued effort, ribosome display was applied to the affinity maturation of the ZRAF322 variant in a novel approach, based on repetitive cycles of diversification by error-prone PCR of the entire affibody gene and ribosome display selection, mimicking the principles of natural evolution. The method involved a monitoring of the progress of evolution and variants of ZRAF322 with 13- to 26-fold improved affinities were obtained, that contained different combinations of single or double amino acid substitutions in either previously randomized or framework positions. Implications of the substitutions for binder stability and selectivity were also investigated, showing that a higher affinity could be associated with a lower thermal melting point and that affinity-improved variants showed uncompromised binding selectivity to the hRaf-1 target. / QC 20110506

This thesis describes the construction and characterisation of an insulin-like growth factor (IGF-I)-binding single chain Fv (scFv) and the utilisation of this scFv as a model protein for the study of the application of DNA shuffling and ribosome display to antibody engineering. The variable domain genes were isolated from the hybridoma cell line producing the monoclonal antibody and successfully joined by PCR for the construction of the scFv, named anti-GPE. Sequencing of the gene revealed an unusually short heavy chain CDR2 region. The cloned scFv was expressed in E. coli and purified. Expression levels were low and the protein has poor solubility, most likely due to a reduction in folding efficiency caused by the abbreviated CDR2. The purified monomeric form of the protein was analysed for binding to IGF-I using surface plasmon resonance on the BIAcore 1000 with the specificity of the IgG version of the antibody for the three N-terminal residues of IGF-I - Gly-Pro-Glu - reproduced. The scFv's calculated dissociation constant of 3.68 µM is a low affinity for an antibody and is approximately 36-fold weaker than was calculated for the Fab version of the antibody, but it is concluded that the calculated affinity for the scFv was an apparent affinity that may be an underestimation of true affinity due to the presence of non-functional or misfolded scFv species within the gel-filtration purified monomer peaks. A mutant version of anti-GPE with residues inserted in the CDR2 to restore it to normal length produced a protein with improved expression and solubility characteristics while retaining IGF-I-binding. It was concluded that the short CDR2 was due to deletions generated during the somatic mutation process and a model for this is described. A ribosome display method using a rabbit reticulocyte lysate as a source of ribosomes was developed for specific selection of anti-GPE against IGF-I. Error prone PCR was used to produce a random point mutated library of anti-GPE (EPGPE). This was taken through several cycles of display and selection but selection for non-specifically binding scFvs was commonly observed. This was probably due to poor folding of ribosome-displayed proteins in the system used, possibly caused by the presence of DTT in the lysate and/or the low capacity of the anti-GPE framework to tolerate mutation while retaining stability. It is assumed misfolds, exposing hydrophobic regions, would have a tendency to non-specifically interact with the selection surface. Of the 64 EPGPE clones screened from four rounds of display and selection, many were shown to have poor or non-specific binding, but one scFv was characterised that was affinity matured 2.6-fold over anti-GPE wild type affinity for IGF-I. A DNA shuffling method was developed to produce libraries of chimaeric scFvs between anti-GPE and NC10 (anti-neuraminidase scFv) with the objective of isolating functional IGF-I-binding chimaeras. The NC10 scFv had its CDRs replaced with the anti-GPE CDRs prior to the shuffling to increase the likelihood of isolating IGF-I binders. Ribosome display was used for selection from the chimaera libraries. Selection strategies included elution of specific binders by GPE peptide and a GPE 10-mer peptide. Selection was also performed using IGF-I immobilised on a BIAcore sensorchip as a selection surface. Again, much non-specific selection was observed as seen for display of EPGPE, for what was expected to be the same reasons. Selected scFvs were genuinely chimaeric but with poor expression and solubility and mostly non-specific in their binding. One characterised selected chimaera, made up of three segments of each of the parental scFvs, was shown to bind specifically to IGF-I by BIAcore. Steps to improve the efficiency of the ribosome display system have been identified and are discussed.

Fast and precise quantification of circulating tumour cells (CTC) in lung adenocarcinoma is a pivotal step in acceleration of diagnosis, selection of early therapy and estimation of treatment prognosis. Development of a new type of microfluidic device based on detection and quantification of epithelial- and mesenchymal-type CTC by high-affinity and cell-type specific protein binders anchored to a microfluidic chip surface represents a highly innovative approach. In this work, we used EpCAM membrane glycoprotein as a target for generation of epithelial cell- specific protein binders by a directed evolution of proteins selected from highly complex combinatorial libraries derived from albumin-binding domain scaffold (ABD) or human muscle protein domain-derived "Myomedin" scaffold. Collections of EpCAM-binding candidates from the both used libraries were generated and particular binding variants were further characterized by DNA sequencing, biochemically and by functional cell-surface binding assays. The best candidates might serve as robust anchor proteins of a microfludic chip. Key words: epithelial cell, EpCAM, protein binder, ribosome display, combinatorial library, protein scaffold