Ion Channel Activity of Transmembrane Segment 3 of E. coli MntH in the Presence of Manganese

E. coli MntH (Proton-dependent Manganese Transporter) represents a good prototypic model to advance understanding of structure-function relationship in the Nramp family of secondary active transporters of divalent metal ions present in virtually all living organisms. Despite its key physiological role, the information about bacterial MntH structure and transport mechanism remains limited in part due to the lack of appropriate experimental techniques. In this study, a synthetic peptide corresponding to the third transmembrane segment (TMS3) of E. coli MntH, which contains functionally important conserved amino acid residues, was used as an alternative model for studying its structure and interaction with biological membranes. The secondary structure of TMS3 was determined in model membranes and membrane-mimicking organic environments, using CD spectroscopy. The conformation of the peptide exhibited ordered α− and β−conformations in these milieus. Furthermore, electrophysiological measurements (patch-clamp technique) demonstrated that TMS3 was able to form ion channels in model membranes in the presence, but not in the absence, of manganese as a physiological substrate of MntH. Thus, TMS3 retains some functional characteristics of the full-length protein. These findings imply the functional importance of TMS3 and provide a useful experimental approach to study MntH.