Expression of MB109 in E. coli cells and purification of the isolated inclusion bodies. (A) Amino acid sequence of the MB109 polypeptide expressed in this study. The first methionine (bold) is engineered to serve as translational start. The seven conserved cysteine residues are highlighted in gray. (B) Reduced SDS-PAGE gel of the expressed MB109 protein. Lane 2 and 3 are whole cell lysates before and after IPTG induction, respectively. Lane 4 and 5 are supernatant and pellet, respectively, of the IPTG-induced cell lysate. Lane 6 is isolated inclusion bodies. The black arrow indicates the monomeric MB109 protein. (C) Size exclusion chromatographic profiles of Superdex 200 16/60 (left-upper panel) and Superdex 75 16/60 (right-upper panel) loaded with the isolated inclusion bodies. Bottom panels are reduced SDS-PAGE gel images of each corresponding elution fractions. Gray bars highlight the fractions containing MB109 monomers. The black arrows indicate the monomeric MB109 protein.