Biology subjects

Nishizawa, T.

Publications and source records attributed to Nishizawa, T..

3 recordsLinked to original sources

bioRxiv2018

X-ray structures of human ETB receptor provide mechanistic insight into receptor activation and partial activation

Endothelin receptors (ETA and ETB) are class A GPCRs activated by vasoactive peptide endothelins, and are involved in blood pressure regulation. ETB-selective signaling induces vasorelaxation, and thus selective ETB agonists are expected to be utilized for improved anti-tumour drug delivery and neuroprotection. The effectiveness of a highly ETB-selective endothelin analogue, IRL1620, has been investigated in clinical trials. Here, we report the crystal structures of human ETB receptor in complex with ETB-selective agonists, endohelin-3 and IRL1620. The 2.0 [A]-resolution structure of the endothelin-3-bound receptor revealed that the disruption of water-mediated interactions between W6.48 and D2.50, which are highly conserved among class A GPCRs, is critical for receptor activation. These hydrogen-bonding interactions are partially preserved in the IRL1620-bound structure, and a functional analysis revealed the partial agonistic effect of IRL1620. The current findings clarify the detailed molecular mechanism for the coupling between the orthosteric pocket and the G-protein binding, and the partial agonistic effect of IRL1620, thus paving the way for the design of improved agonistic drugs targeting ETB.

molecular biology↗

bioRxiv2018

Cryo-EM structure of the volume-regulated anion channel LRRC8

Maintenance of cell volume against osmotic change is crucial for proper cell functions, such as cell proliferation and migration. The leucine-rich repeat-containing 8 (LRRC8) proteins are anion selective channels, and were recently identified as pore components of the volume-regulated anion channels (VRACs), which extrude anions to decrease the cell volume upon cell-swelling. Here, we present the human LRRC8A structure, determined by a single-particle cryo-electron microscopy analysis. The sea anemone-like structure represents a trimer of dimers assembly, rather than a symmetrical hexameric assembly. The four-spanning transmembrane region has a gap junction channel-like membrane topology, while the LRR region containing 15 leucine-rich repeats forms a long twisted arc. The channel pore is along the central axis and constricted on the extracellular side, where the highly conserved polar and charged residues at the tip of the extracellular helix contribute to the anion and other osmolyte permeability. Comparing the two structural populations facilitated the identification of both compact and relaxed conformations, suggesting that the LRR region is flexible and mobile with rigid-body motions, which might be implicated in structural transitions upon pore opening. Overall, our structure provides a framework for understanding the molecular mechanisms of this unique class of ion channels.

molecular biology↗

bioRxiv2017

Structure of the triose-phosphate/phosphate translocator reveals the basis of substrate specificity

The triose-phosphate/phosphate translocator (TPT) catalyzes the strict 1:1 exchange of triose phosphate, 3-phosphoglycerate and inorganic phosphate across the chloroplast envelope, and plays crucial roles in photosynthesis. Despite rigorous studies for more than 40 years, the molecular mechanism of TPT is poorly understood due to the lack of structural information. Here we report crystal structures of TPT bound to two different substrates, 3-phosphoglycerate and inorganic phosphate, in occluded conformations. The structures reveal that TPT adopts a 10-transmembrane drug/metabolite transporter fold. Both substrates are bound within the same central pocket, where conserved lysine, arginine, and tyrosine residues recognize the shared phosphate group. A structural comparison with the outward-open conformation of the bacterial drug/metabolite transporter suggests a rocking-type motion of helix bundles, and molecular dynamics simulations support a model in which this helix rocking is tightly coupled to the substrate binding, to ensure strict 1:1 exchange. These results reveal the unique mechanism of sugar phosphate/phosphate exchange by TPT.

biochemistry↗