Two-step purification of the outer membrane transporter and activator protein ShlB from Escherichia coli using internally His6-tagged constructs.

ShlB from Serratia marcescens was isolated and purified from a porin-deficient Escherichia coli BL21 strain using a combination of detergent extraction, affinity and ion-exchange chromatography. An internal histidine affinity tag was introduced that did not interfere with activity. At each stage of the purification scheme biological activity of the ShlB protein was assessed. Using this scheme, several His(6)-tagged mutants of ShlB were purified to electrophoretic homogeneity.