Single Domain Antibodies Targeting Receptor Binding Pockets of NadA Restrain Adhesion of to Human Brain Microvascular Endothelial Cells.

adhesin A (NadA), one of the surface adhesins of (NM), interacts with several cell types including human brain microvascular endothelial cells (hBMECs) and play important role in the pathogenesis. Receptor binding pockets of NadA are localized on the globular head domain (A to K) and the first coiled-coil domain (L to K). Here, the phage display was used to develop a variable heavy chain domain (VHH) that can block receptor binding sites of recombinant NadA (rec-NadA). A phage library displaying VHH was panned against synthetic peptides (NadA-gd or NadA-cc), gene encoding VHH was amplified from bound phages and re-cloned in the expression vector, and the soluble VHHs containing disulfide bonds were overexpressed in the SHuffle . From the repertoire of 96 clones, two VHHs (VHH-binding NadA-gd and VHH-binding NadA-cc) were finally selected as they abrogated the interaction between rec-NadA and the cell receptor. Preincubation of NM with VHH and VHH significantly reduced the adhesion of NM on hBMECs and hindered the traversal of NM across the BBB model. The work presents a phage display pipeline with a single-round of panning to select receptor blocking VHHs. It also demonstrates the production of soluble and functional VHHs, which blocked the interaction between NadA and its receptor, decreased adhesion of NM on hBMECs, and reduced translocation of NM across BBB . The selected NadA blocking VHHs could be promising molecules for therapeutic translation.