Interactions of ribose-binding proteins with protein components of translocation system in E. coli

Abstract

Interactions of ribose binding protein (RBP) with protein components of the translocation system of E. coli such as cytoplasmic membrane, cytosolic factor, SecA, and SecB were studied in order to investigate the export mechanism of RBP into periplasm. Native precursor ribose binding protein (pRBP) directly interacted with cytoplasimic membrane protein from the cross-linkage experiment. Although the molecular weight of the cross-linked complex suggests that the precursor protein binds with SecY, this has not been confirmed. The mature ribose binding protein (mRBP) did not bind to any membrane component. Unfolded pRBP cross-linked to an undefined cytosolic factor when diluted with cytosolic extract but this was not observed for mRBP. The folding rate of the unfolded pRBP was retarded by the cytosolic extract. Both unfolded and folded pRBP were cross-linked to SecB. The binding of the precursor protein to SecB was also apparent from the intrinsic fluorescence of SecB tryptophan. In addition to the interaction of pRBP with other proteins, SecA and SecB interactions with model membrane vesicle containing acidic phospholipid was performed. SecA was bound to the vesicles with concomitant structural change but SecB did not show this effect. The secondary structure was also studies by circular dichroism.