Summary
A bioRxiv preprint reports cryo-EM structures of human VIAAT in two states, identifying a GABA-binding pocket and a proposed gate that opens toward the synaptic-vesicle interior.
A bioRxiv preprint reports cryo-EM structures of human VIAAT, the transporter that loads the inhibitory neurotransmitters GABA and glycine into synaptic vesicles. The researchers captured VIAAT without bound GABA in a luminal-open state and with GABA bound in an occluded state. They identify a group of four amino acids that helps recognise GABA and propose that one of them acts as a gate for release into the vesicle.
GABA and glycine help restrain neuronal activity and stabilise neural circuits. Understanding how VIAAT handles these molecules can clarify a basic step in inhibitory signalling: packaging neurotransmitters inside vesicles before they are released at synapses.
What the structures show
The study describes VIAAT as an 11-transmembrane-helix protein with a LeuT-like fold, a structural arrangement the authors say differs from those of other vesicular neurotransmitter transporters. In its central pocket, Phe133, Tyr221, Phe315 and Phe322 form an aromatic cage that the researchers identify as important for GABA recognition.
A comparison of the two structures points to Phe315 as a luminal gate. In the proposed mechanism, this residue rotates away from the central pocket, opening a pathway on the vesicle-facing side through which the substrate can be released. The structures are snapshots of different states; the authors also use a cytosolic-facing model to help interpret transport across the membrane.
The researchers report functional neuronal rescue experiments alongside the structural work. Together, these approaches connect the proposed transport mechanism with VIAAT’s role in neurons, although the supplied abstract does not give details of the rescue experiments.
Relevance to inhibitory signalling
VIAAT transports both GABA and glycine, but the structures described here focus on GABA recognition. The authors say their findings provide a framework for understanding how epilepsy-associated VIAAT variants may impair inhibitory neurotransmission. This is a mechanistic basis for studying those variants, rather than a clinical finding about epilepsy or a treatment result.
The work is presented as a bioRxiv preprint. Its central contribution is a structural account of how human VIAAT binds GABA and how a specific residue may open the vesicle-facing route for substrate release.