In vivo phosphorylation of a peptide tag for protein purification

Abstract

Objectives: To design a new system for the in vivo phosphorylation of proteins in Escherichia coli using the co-expression of the α-subunit of casein kinase II (CKIIα) and a target protein, (Nanofitin) fused with a phosphorylatable tag.

Results: The level of the co-expressed CKIIα was controlled by the arabinose promoter and optimal phosphorylation was obtained with 2 % (w/v) arabinose as inductor. The effectiveness of the phosphorylation system was demonstrated by electrophoretic mobility shift assay (NUT-PAGE) and staining with a specific phosphoprotein-staining gel. The resulting phosphorylated tag was also used to purify the phosphoprotein by immobilized metal affinity chromatography, which relies on the specific interaction of phosphate moieties with Fe(III).

Conclusion: The use of a single tag for both the purification and protein array anchoring provides a simple and straightforward system for protein analysis.

Keywords: Casein kinase II; Nanofitin; Phosphorylated peptide tag; Phosphorylation; Protein purification.