As expected, no binding to CHO-WT cells was observed (Figure 3). Open in a separate window Figure 2. RB49 VH domain IMGT collier de perles representation. in position 125 on the heavy chain alters the xiRB49 CDR3 light chain conformation and its mutation to threonine allows complete functional recovery. KEYWORDS: Monoclonal antibody, chimerization, proline, approaches combined with experiments. These results highlighted that the proline at position 125 in the heavy chain of xiRB49 alters the relative conformation of complementarity-determining regions (CDRs), while its mutation to threonine produces a fully functional xiRB49-P125T. Results xiRB49 expression and functionality xiRB49 was expressed in ExpiCHOTM cells and purified on a protein A column, suggesting correct refolding of the constant IgG1 domain (Figures S1 and S2a). Moreover, we observed, on SDS PAGE, in nonreducing conditions, a band at 150 kDa and in reduced conditions two bands corresponding to the heavy and light chains 50 kDa and 25 kDa, respectively (Figure S2b). We determined a hydrodynamic radius (Rh) of 5.2??0.4?nm and no aggregation was detected (Figure S2C). Identical results were obtained for our positive control, the chimeric Rendomab A63, xiRA63, already described for theranostic applications to ETA+ tumors.12 We assessed the functionality of xiRB49 and RB49 by their binding to CHO-ETB cells compared to CHO-WT cells (Figure 1). No recognition for ETB was observed with xiRB49. In contrast, RB49 was fully functional with an apparent Kd?=?0.91??0.01?nM and a Bmax value (maximal Binding ability of the antibody) of 83.5??0.09% MFI (Mean Fluorescence Intensity). No RB49 cross-reaction was detected with CHO-WT cells, highlighting its specificity. Open in a separate window Figure 1. Antibody functionality assay. (a) FACS binding curves of RB49 (black) and xiRB49 (red). MAb specificity was assessed with CHO-ETB (solid line) and CHO-WT (dotted line). (b) Table of apparent Kd (nM) and Bmax (% MFI) for RB49 and xiRB49. Data are presented as mean??SD. As RB49 was purified from hybridoma, we decided to produce its recombinant format (reRB49) in ExpiCHO cells to evaluate its functionality. FACS (Fluorescence Activated Cell Sorter) binding curves indicated that reRB49 was fully functional with identical RB49 parameters (Figure S3). This indicates that the origin of the loss of ETB recognition by RB49 variable regions is due to the chimerization process with the human IgG1Kappa isotype. A careful analysis of variable sequences allowed us to identify an unusual proline at position 125. Indeed, no proline is encoded by the mouse genome in the FR4 AGN 192836 domain (Figure S4).The RB49 VH domain is AGN 192836 represented according to the IMGT rules and numbering. The unusual proline is circled in green (Figure 2). As the canonical amino acid at this position is threonine, we decided to explore the functionality of the xiRB49-P125T mutant. A fully functional xiRB49-P125T was restored, as confirmed by its binding curves, with an apparent affinity similar to that of RB49. As expected, no binding to CHO-WT cells was observed (Figure 3). Open in a separate window Figure 2. RB49 VH domain IMGT collier de perles representation. (a) All hydrophobic amino acids are in blue and amino acids conserved positions in all immunoglobulins in green. Squares represent the anchor positions which delimit the CDR-IMGT (framed in color, red CDR1, orange CDR2, purple CDR3) and framework IMGT (framed in black) regions. Hatched circles correspond to missing positions according to IMGT unique numbering for variable domain. The direction of the beta strands is AGN 192836 represented by black arrows. Unusual proline is circled in green (b) proline and threonine chemical structures are presented. Open in Rabbit Polyclonal to Estrogen Receptor-alpha (phospho-Tyr537) a separate window Figure 3. FACS binding curves of RB49 and xiRB49-P125T. (a) RB49 (black) and xiRB49-P125T (green) for CHO-ETB (solid line) and CHO-WT (dashed line). (b) Apparent Kd (nM) and Bmax (% MFI) are indicated in the table. Data are presented as mean??SD. A two-tailed paired students t-test was used for data comparison. Study of the disruptive role of proline in the RB49 chimerization process To understand the influence of proline on the stability of the chimeric RB49, we performed thermal denaturation experiments. We obtained two inflection temperatures Ti1 and Ti2 for xiRB49 and the mutant xiRB49-P125T reflecting two transition states in the protein unfolding process (Figure 4a). For Ti1, reflecting AGN 192836 the CH2/CH3 domain denaturation, no difference was observed between xiRB49 Ti1?=?74.4C and xiRB49-P125T Ti1?=?74C. In contrast, for Ti2, reflecting Fab denaturation, a difference of 4.1C was.