A Loose Relationship: Incomplete H/Sugar Coupling in the MFS Sugar Transporter GlcP.

The glucose transporter from Staphylococcus epidermidis, GlcP, is a homolog of the human GLUT sugar transporters of the major facilitator superfamily. Together with the xylose transporter from Escherichia coli, XylE, the other prominent prokaryotic GLUT homolog, GlcP, is equipped with a conserved proton-binding site arguing for an electrogenic transport mode. However, the electrophysiological analysis of GlcP presented here reveals important differences between the two GLUT homologs.

Flexibility of the N-terminal mVDAC1 segment controls the channel's gating behavior.

Since the solution of the molecular structures of members of the voltage dependent anion channels (VDACs), the N-terminal α-helix has been the main focus of attention, since its strategic location, in combination with its putative conformational flexibility, could define or control the channel's gating characteristics. Through engineering of two double-cysteine mVDAC1 variants we achieved fixing of the N-terminal segment at the bottom and midpoint of the pore. Whilst cross-linking at the midpoint resulted in the channel remaining constitutively open, cross-linking at the base resulted in an "asymmetric" gating behavior, with closure only at one electric field's orientation depending on the channel's orientation in the lipid bilayer.