Gomez, Y. K. | bioRxiv Science

bioRxiv2022

Allosteric Regulation of a Synaptic Vesicle Glutamate Transporter

Concentration of neurotransmitter inside synaptic vesicles (SVs) underlies the quantal nature of synaptic transmission. In contrast to many transporters, SV uptake of the principal excitatory neurotransmitter glutamate is driven by membrane potential. To prevent nonquantal efflux of glutamate after SV exocytosis, the vesicular glutamate transporters (VGLUTs) are allosterically inhibited by the neutral pH of the synaptic cleft. We have now determined high-resolution structures of VGLUT2 with a cyclic analog of glutamate bound that defines the mechanism of substrate recognition, a positively charged cytoplasmic vestibule that electrostatically attracts the negatively charged substrate, and modification by palmitoylation that promotes retrieval of the transporter after exocytosis. The structure also incorporates an extensive, cytoplasmic network of electrostatic interactions that acts as a gate. Functional analysis shows how this cytoplasmic gate confers the allosteric requirement for lumenal H+ required to restrict VGLUT activity to SVs.

biochemistry↗

bioRxiv2020

Robust Sequence Determinants of α-Synuclein Toxicity in Yeast Implicate Membrane Binding

Protein conformations are shaped by cellular environments, but how environmental changes alter the conformational landscapes of specific proteins in vivo remains largely uncharacterized, in part due to the challenge of probing protein structures in living cells. Here, we use deep mutational scanning to investigate how a toxic conformation of -synuclein, a dynamic protein linked to Parkinsons disease, responds to perturbations of cellular proteostasis. In the context of a course for graduate students in the UCSF Integrative Program in Quantitative Biology, we screened a comprehensive library of -synuclein missense mutants in yeast cells treated with a variety of small molecules that perturb cellular processes linked to -synuclein biology and pathobiology. We found that the conformation of -synuclein previously shown to drive yeast toxicity--an extended, membrane-bound helix--is largely unaffected by these chemical perturbations, underscoring the importance of this conformational state as a driver of cellular toxicity. On the other hand, the chemical perturbations have a significant effect on the ability of mutations to suppress -synuclein toxicity. Moreover, we find that sequence determinants of -synuclein toxicity are well described by a simple structural model of the membrane-bound helix. This model predicts that -synuclein penetrates the membrane to constant depth across its length but that membrane affinity decreases toward the C terminus, which is consistent with orthogonal biophysical measurements. Finally, we discuss how parallelized chemical genetics experiments can provide a robust framework for inquiry-based graduate coursework.

biochemistry↗