Isolation and optimization of camelid single-domain antibodies: Dirk Saerens’ work on nanobodies

An efficient protocol towards site-specifically clickable nanobodies in high yield: cytoplasmic expression in Escherichia coli combined with intein-mediated protein ligation

In this study, several expression strategies were investigated in order to develop a generic, highly productive and efficient protocol to produce nanobodies modified with a clickable alkyne function at their C-terminus via the intein-mediated protein ligation (IPL) technique. Hereto, the nanobody targeting the vascular cell adhesion molecule 1 (NbVCAM1) was used as a workhorse. The highlights of the protocol can be ascribed to a cytoplasmic expression of the nanobody-intein-chitin-binding domain fusion protein in the Escherichia coli SHuffle(®) T7 cells with a C-terminal extension, i.e. LEY, EFLEY or His6 spacer peptide, in the commonly used Luria-Bertani medium. The combination of these factors led to a high yield (up to 22 mg/l of culture) and nearly complete alkynation efficiency of the C-terminally modified nanobody via IPL. This yield can even be improved to ∼45 mg/l in the EnPresso(®) growth system but this method is more expensive and time-consuming. The resulting alkynated nanobodies retained excellent binding capacity towards the recombinant human VCAM1. The presented protocol benefits from time- and cost-effectiveness, which allows a feasible production up-scaling of generic alkynated nanobodies. The production of high quantities of site-specifically modified nanobodies paves the way to new biosurface applications that demand for a homogeneously oriented nanobody coupling. Prospectively, the alkynated nanobodies can be covalently coupled to a multitude of azide-containing counterparts, e.g. contrast labeling agents, particles or surfaces for numerous innovative applications.

A conformation-based phage-display panning to screen neutralizing anti-VEGF VHHs with VEGFR2 mimicry behavior

The potency of VEGF-based anti-angiogenic strategies in cancer therapy and the brilliant characteristics of VHHs motivated us to directly block VEGF binding to its receptor with neutralizing single domain antibodies, thereby fading away the VEGF signaling pathway. Considering with high resolution crystal structure of VEGF-RBD/VEGFR2 complex, we could adopt a combinatorial screening strategy: stringent panning and competition ELISA, to direct the panning procedure to dominantly screen the favorable binders that bind and block the key functional regions of VEGF. Based on competition assay, the majority of the screened clones (82%) showed the VEGFR2 mimicry behavior for binding to VEGF molecule. The phage pool gets enriched in favor of sequences that bind the receptor binding sites of VEGF. Different immunoassays and molecular docking simulation verified that all selected VHHs could bind and cover the receptor binding sites of VEGF. Consequently, some modifications in panning procedure with considering the structural features and detailed information of functional regions of a protein antigen, led us to successfully trap the high-affinity specific binders against its hot functional regions. Since the selected VHHs could cover the receptor binding site of VEGF and block VEGF binding to the receptor, they might be promising candidates for anti-angiogenic therapies.