VMAT2 transport and inhibition mechanisms revealed by cryo-EM
Neurotransmitters are a class of signaling chemicals, including monoamines such as serotonin, dopamine, and histamine, which play a vital role in a variety of neurological activities, including mood, memory, growth and development, and drug addiction. The cytosolic neurotransmitters in presynaptic neurons must be transported into synaptic vesicles for storage and subsequent release. The package of monoamines into vesicles is mediated by the vesicular monoamine transporter protein VMAT2. Importantly, several drugs that target on VMAT2 have been used to treat hypertension and hyperactivity disorders.
Human VAMT2 is a small membrane protein with a molecular weight of only 56 kDa, making it extremely difficult for cryo-EM analysis. Prof. Jiang Daohua's group successfully overcame the challenges by screening fusion proteins, and reconstructed the high-resolution structures of VMAT2 binding to three clinical drugs and the substrate serotonin. Combining with functional experiments and molecules dynamic simulations, they described the molecular mechanisms of substrate recognition and drug inhibition of VMAT2.
The cryo-EM structures were determined in cytoplasm facing, occluded and lumen facing states, representing three typical conformations in the transport cycle of VMAT2. The structures also revealed the inhibitory mechanisms of different drugs. For example, reserpine competes with serotonin for binding to the cytoplasm facing VMAT2, but tetrabenazine and ketanserin stabilize VMAT2 in occluded and lumen facing states, respectively. In addition, the structures provide important insights into understanding the distinct pharmacological properties of reserpine, tetrabenazine and ketanserin. Moreover, the serotonin-bound VMAT2 adopts a lumen-facing conformation, a state favoring substrate release.
This study advances the comprehension of VMAT2 functions and facilitates the mechanistic understanding of substrate recognition, drug inhibition, and drug development of VMAT2. Meanwhile, the strategy of VMAT2 fusion protein used in this study could be applied to other small membrane proteins, which will facilitate the structure analysis of membrane transporter proteins and other small proteins by cryo-EM.
This study entitled "Transport and inhibition mechanism of human VMAT2" was published on Nature. Link for the article：https://www.nature.com/articles/s41586-023-06926-4。
This study was supported by the National Natural Science Foundation of China, The Chinese Academy of Sciences and The Institute of Physics.
Figure 1. Cryo-EM structures of VMAT2 in complex with distinct ligands. (Image from Institute of Physics, SM10)
Institute of Physics, Laboratory of Soft Matter Physics.
VMAT2; Monoamine neurotransmitters; Cryo-EM; Transport mechanism; Drug inhibition
Vesicular monoamine transporter 2 (VMAT2) accumulates monoamines in presynaptic vesicles for storage and exocytotic release, playing a vital role in monoaminergic neurotransmission. Dysfunction of monoaminergic systems causes many neurological and psychiatric disorders, including Parkinson's disease, hyperkinetic movement disorders, and depression, which can benefit from drug intervention of VMAT2 activities. Suppressing VMAT2 by reserpine and tetrabenazine alleviates symptoms of hypertension and Huntington's disease, respectively. Despite its biological and pharmacological importance, the precise molecular mechanisms by which VMAT2 recognizes monoamines and drugs remain unknown. Here, we describe the cryo-electron microscopy structures of human VMAT2 complexed with serotonin and three clinical drugs at 3.5-2.8 Å, demonstrating the structural basis for VMAT2 transport and inhibition. Reserpine and ketanserin occupy the substrate-binding pocket and lock VMAT2 in cytoplasm-facing and lumen-facing states, respectively, whereas tetrabenazine binds in a VMAT2-specific pocket and traps VMAT2 in an occluded state. Moreover, the structures in three distinct states reveal the structural basis of the VMAT2 transport cycle. Our study establishes a structural foundation for the mechanistic understanding of substrate recognition, transport, drug inhibition, and pharmacology of VMAT2 while shedding light on the rational design of potential therapeutics.