Fig. 3.

Analysis of Fab assembly and expression of APEx two-hybrid system. (A) A schematic diagram of Fab assembly and expression analysis by APEx two-hybrid. The light chain is coexpressed with heavy chain fused to a FLAG tag. Antibody assembly occurs in the periplasm and, after spheroplasting, the cells are labeled with anti-FLAG-PE and PA-FITC, which were used to detect Fab expression and antigen binding, respectively. (B and C) Cells expressing M18.1 hum Fab were grown at different temperatures [37°C (white) and 25°C (red)] and labeled with anti-FLAG-PE (B) or PA-FITC (C), which represent expression and antigen binding, respectively. (D) Fab was expressed in soluble form in cells grown at both temperatures, and the yields of antigen binding Fabs were analyzed by ELISA.