HISTIDINE-419 PLAYS A ROLE IN ENERGY COUPLING IN THE VESICULAR MONOAMINE TRANSPORTER FROM RAT

Vesicular monoamine transporters (VMAT) catalyze transport of serotoni n, dopamine, epinephrine and norepinephrine into subcellular storage o rganelles in a variety of cells. Accumulation of the neurotransmitter depends on the proton electrochemical gradient across the organelle me mbrane and involves VMAT-mediated exchange of two lumenal protons with one cytoplasmic amine. It has been suggested in the past that His res idues play a role in H+ movement or in its coupling to active transpor t in H+-symporters and antiporters. Indeed VMAT-mediated transport is inhibited by reagents specific for His residues. We have identified on e His residue in VMAT1 from rat which is conserved in other vesicular neurotransmitter transporters. Mutagenesis of this His (H419) to eithe r Arg or Cys completely inhibits [H-3]serotonin and [H-3]dopamine accu mulation. Mutagenesis also inhibits other H+-dependent partial reactio ns of VMAT such as the acceleration of binding of the high affinity li gand reserpine, but does not inhibit the [H-3]reserpine binding which is not dependent on H+ translocation. It is concluded that His-419 pla ys a role in energy coupling in r-VMAT1.