Drug inhibition and substrate alternating flipping mechanisms of human VMAT2

Vesicular monoamine transporters (VMAT1/2) are responsible for loading and packaging monoamine neurotransmitters into synaptic vesicles, including serotonin (5-HT), dopamine (DA), norepinephrine, and histamine. Dysregulation of VMAT2 within the central nervous system can lead to schizophrenia, mood disorders, and Parkinsons disease, due to the imbalances of these monoamine neurotransmitters. Medications such as tetrabenazine (TBZ) and valbenazine (VBZ) targetting VMAT2 are approved for treating chorea associated with Huntingtons disease and Tardive Dyskinesia. Our cryo-EM studies and molecular dynamics (MD) simulations on VMAT2 bound to drug inhibitors (TBZ and VBZ) and substrates (5-HT and DA), unveil the inhibition mechanism of VMAT2, alternating flipping mechanism of substrates during loading, translocation, and release, as well as the interplay between protonation of crucial acidic residues and substrate release. These findings enhance the understanding of VMAT-mediated monoamine neurotransmitter transport, fostering drug development for neurological and neuropsychiatric disorders, with a specific emphasis on VMATs.