SDS-PAGE analysis of recombinant BgpA. Lanes: M, molecular mass standard; 1, crude extract of C41(DE3) carrying pGEX-bgpA; 2, GST-BgpA enzyme fraction after glutathione-Sepharose chromatography; 3, enzyme fraction after DEAE anion-exchange chromatography and removal of the GST epitope by thrombin; 4, recombinant BgpA after Mono Q anion-exchange chromatography.