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Structural basis of cytoplasmic NaV1.5 and NaV1.4 regulation.

ABSTRACT: Voltage-gated sodium channels (NaVs) are membrane proteins responsible for the rapid upstroke of the action potential in excitable cells. There are nine human voltage-sensitive NaV1 isoforms that, in addition to their sequence differences, differ in tissue distribution and specific function. This review focuses on isoforms NaV1.4 and NaV1.5, which are primarily expressed in skeletal and cardiac muscle cells, respectively. The determination of the structures of several eukaryotic NaVs by single-particle cryo-electron microscopy (cryo-EM) has brought new perspective to the study of the channels. Alignment of the cryo-EM structure of the transmembrane channel pore with x-ray crystallographic structures of the cytoplasmic domains illustrates the complementary nature of the techniques and highlights the intricate cellular mechanisms that modulate these channels. Here, we review structural insights into the cytoplasmic C-terminal regulation of NaV1.4 and NaV1.5 with special attention to Ca2+ sensing by calmodulin, implications for disease, and putative channel dimerization.

SUBMITTER: Nathan S

PROVIDER: S-EPMC7953540 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:In plants triosephosphate isomerase (TPI) interconverts glyceraldehyde 3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP) during glycolysis, gluconeogenesis, and the Calvin-Benson cycle. The nuclear genome of land plants encodes two tpi genes, one gene product is located in the cytoplasm and the other is imported into the chloroplast. Herein we report the crystal structures of the TPIs from the vascular plant Arabidopsis thaliana (AtTPIs) and address their enzymatic modulation by redox agents. Cytoplasmic TPI (cTPI) and chloroplast TPI (pdTPI) share more than 60% amino acid identity and assemble as (?-?)8 dimers with high structural homology. cTPI and pdTPI harbor two and one accessible thiol groups per monomer respectively. cTPI and pdTPI present a cysteine at an equivalent structural position (C13 and C15 respectively) and cTPI also contains a specific solvent accessible cysteine at residue 218 (cTPI-C218). Site directed mutagenesis of residues pdTPI-C15, cTPI-C13, and cTPI-C218 to serine substantially decreases enzymatic activity, indicating that the structural integrity of these cysteines is necessary for catalysis. AtTPIs exhibit differential responses to oxidative agents, cTPI is susceptible to oxidative agents such as diamide and H2O2, whereas pdTPI is resistant to inhibition. Incubation of AtTPIs with the sulfhydryl conjugating reagents methylmethane thiosulfonate (MMTS) and glutathione inhibits enzymatic activity. However, the concentration necessary to inhibit pdTPI is at least two orders of magnitude higher than the concentration needed to inhibit cTPI. Western-blot analysis indicates that residues cTPI-C13, cTPI-C218, and pdTPI-C15 conjugate with glutathione. In summary, our data indicate that AtTPIs could be redox regulated by the derivatization of specific AtTPI cysteines (cTPI-C13 and pdTPI-C15 and cTPI-C218). Since AtTPIs have evolved by gene duplication, the higher resistance of pdTPI to redox agents may be an adaptive consequence to the redox environment in the chloroplast.

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Structural basis of cytoplasmic NaV1.5 and NaV1.4 regulation.

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