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Regarding the importance of inhibiting VEGF and unique features of VHHs as a new generation of antibody-based therapeutics, the present study aimed to generate VHHs against the receptor binding domain of VEGF, thereby blocking of VEGF binding to its receptor. After preparing the gene repertoire of VHH fragments from an immunized camel, a VHH phage display library was constructed. We adopted a stringent successive biopanning to isolate the phages displaying VHH with high affinity to VEGF-RBD.A significant enrichment of phages that specifically bound to the target protein was obtained after six rounds of panning. Of the specific clones with high binding affinity screened by monoclonal phage ELISA, 52% shared the same VHH sequence, showing its high enrichment. Using molecular simulation of antigen-antibody interaction based on the crystallographic information of VEGF/VEGFR2, molecular dynamics simulations and MM/PBSA free energy calculations, we provide a reliable picture of the binding site of antibody on antigen. The key residues in the VEvhh1-VEGF interface were dissected and the energetics was analyzed by MM/PBSA. The results of studies revealed that VEvhh1 binds to the receptor binding site of VEGF with high binding energy and showed the highest affinity to the residues of VEGF which are responsible for VEGF binding to VEGFR2. Also the antibody potently covers these key functional residues of VEGF, thereby inhibiting VEGF binding to its receptor and probably abrogating its biological activity. This study may represent VEvhh1 as an anti-VEGF and anti-angiogenic candidate.

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Purpose: The antigen binding fragments of camelids heavy chain antibodies are comprised in one single domain (VHH). The crystal structure of an isolated VHH indicated that it is a problate particle of 2.5 nm in diameter and ∼ 4 nm high, and has been referred to as a nanobody. The very close similarity of these molecules to human VHs illustrates the potential application of these novel products as an immunodiagnostic immunotherapeutic reagent. One of the key components in production, characterization and application of nanobodies in detection is the anti-nanobodiy HRP conjugate. Materials and Methods: Here, we report high expression and purification of some nanobodies against tumor markers. The nanobodies genes were sub-cloned into a pSJF9 vector to over-express the protein coupled with fusion tags in E. coli TG1. The expressed nanobodies were purified by immobilized metal affinity chromatography (IMAC). Described here is the preparation, purification and characterization of anti-nanobody antibody HRP conjugate for use in the various nanobody detection systems. Results: Analysis by SDS-PAGE and Western blotting demonstrated the integrity of the purified nanobodies. Because of application of several biochemical modifications, the produced anti-nanobodies HRP conjugate have efficient sensitivity and specificity. Conclusion: By setting the temperature, time and inducer reagent the nanobodies were produced in optimum yield. We concluded that the HRP conjugated anti-nanobody can detect nanobodies in various detection procedures with great sensitivity and accuracy.

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