Coexpression of molecular chaperones to enhance functional expression of anti-BNP scFv in the cytoplasm of <Emphasis Type="Italic">Escherichia coli</Emphasis> for the detection of B-type natriuretic peptide

Molecular chaperones are a ubiquitous family of cellular proteins that mediate the correct folding of other target polypeptides. In our previous study, the recombinant anti-BNP scFv, which has promising applications for diagnostic, prognostic, and therapeutic monitoring of heart failure, was expressed in the cytoplasm of Escherichia coli. However, when the anti-BNP scFv was expressed, 73.4% of expressed antibodies formed insoluble inclusion bodies. In this study, molecular chaperones were coexpressed with anti-BNP scFv with the goal of improving the production of functional anti-BNP in the cytoplasm of E. coli. Five sets of molecular chaperones were assessed for their effects on the production of active anti-BNP scFv. These sets included the following: trigger factor (TF); groES/groEL; groES/groEL/TF; dnaK/dnaJ/grpE; groES/groEL/dnaK/dnaJ/grpE. Of these chaperones, the coexpression of anti-BNP scFv with the groES/groEL chaperones encoded in plasmid pGro7 exhibited the most efficient functional expression of anti-BNP scFv as an active form. Coexpressed with the groES/groEL chaperones, 64.9% of the total anti-BNP scFv was produced in soluble form, which is 2.4 times higher scFv than that of anti-BNP scFv expressed without molecular chaperones, and the relative binding activity was 1.5-fold higher. The optimal concentration of l-arabinose required for induction of the groES/groEL chaperone set was determined to be 1.0 mM and relative binding activity was 3.5 times higher compared with that of no induction with l-arabinose. In addition, soluble anti-BNP scFv was increased from 11.5 to 31.4 μg/ml with optimized inducer concentration (1.0 mM l-arabinose) for the coexpression of the groES/groEL chaperones. These results demonstrate that the functional expression of anti-BNP scFv can be improved by coexpression of molecular chaperones, as molecular chaperones can identify and help to refold improperly folded anti-BNP scFv.