In the nervous system, A→I RNA editing has an important role in regulating neuronal excitability. Ligand-gated membrane receptors, synaptic proteins, as well as ion channels, are targets for recoding by RNA editing. Although scores of editing sites have been identified in the mammalian brain, little is known about the functional alterations that they cause, and even less about the mechanistic underpinnings of how they change protein function. We have previously shown that an RNA editing event (I400 V) alters the inner permeation pathway of human KV1.1, modifying the kinetics of fast inactivation. Here we show that the channel's inactivation gate enters deep into the ion permeation pathway and the very tip establishes a direct hydrophobic interaction with the edited position. By converting I to V, the intimacy of the interaction is reduced, allowing the inactivation gate to unbind with much faster kinetics.

Calcium-activated chloride channels (CaCC) formed by anoctamin1/TMEM16A subunits are ubiquitously expressed, and these channels are known to prevent polyspermy in amphibian oocytes. Here, we describe a TMEM16A clone isolated from Xenopus tropicalis oocytes (xtTMEM16A) and how the anion permeation properties are modified in single-site mutants of the ion pore. The anion permeability sequence was SCN(-) > I(-) > Br(-) > Cl(-) > gluconate (relative permeabilities 5.6:3.0:2.1:1:0.2, respectively). Dose-response curves indicated that the voltage-dependent half-maximal concentration for Ca(2+) activation (K d of the Hill equation at +100 mV) was 120 nM in normal external Cl(-), whereas it was displaced leftward to 75 nM Ca(2+), when I(-) replaced Cl(-). The I(-):Cl(-) mole fraction (MF) of the external solution was varied in order to gain insight into the permeation mechanism of the pore. No anomaly in MF behavior was observed for conductance, but it was observed for current reversal potential, which deviated from the prediction of the Goldman-Hodgkin-Katz equation. Mutations of positively charged amino acids in the pore, R646 and R761, to glutamate resulted in reduction of the relative permeability to I(-). Data from the wild type and mutants could be well fitted by a three-barrier, two-site permeation model. This suggests a multi-ion pore with at least two binding sites for anions, with R646 mole fraction closer to the extracellular membrane surface--being important for the stability of both sites--and R761--located deeper within the membrane--mainly affecting the innermost binding site. Considerations of xtTMEM16A putative pore region topology are discussed in the light of two alternative topological models of the protein.

Significance Immunosuppression by myeloid-derived suppressor cells (MDSC), especially near tumor surfaces, involves the extracellular production of reactive oxygen species (ROS). ROS generation in MDSC occurs during the oxidation of NADPH to NADP+, which NOX2 catalyzes. ROS react with the T cell receptor complex, abolishing the antigen presentation, which blocks the immune system elimination of the tumor cells. Extrusion of protons from MDSC by voltage-gated proton channel (H v 1) sustains ROS production. Here, we demonstrate the expression of H v 1 in mouse MDSC. In this way, H v 1 present in MDSC becomes a potential cancer therapeutic target since its inhibition seems to diminish immunosuppression activity in the tumoral microenvironment, allowing cancer cells to be attacked by the immune system.

The cytosolic reducing agent glutathione can reverse thiol modification of cysteine residues inside the pores of connexins and other channels permeable to large molecules.

We studied the effects of mutations of positively charged amino acid residues in the pore of X. tropicalis TMEM16A calcium-activated chloride channels: K613E, K628E, K630E; R646E and R761E. The activation and deactivation kinetics were not affected, and only K613E showed a lower current density. K628E and R761E affect anion selectivity without affecting Na C permeation, whereas K613E, R646E and the double mutant K613E C R646E affect anion selectivity and permeability to Na C . Furthermore, altered blockade by the chloride channel blockers anthracene-9-carboxylic acid (A-9-C), 4, 4'-Diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS) and T16inh-A01 was observed. These results suggest the existence of 2 binding sites for anions within the pore at electrical distances of 0.3 and 0.5. These sites are also relevant for anion permeation and blockade.

A common phenotype for many genetic diseases is that the cell is unable to deliver full-length membrane proteins to the cell surface. For some forms of autism, hereditary spherocytosis and color blindness, the culprits are single point mutations to cysteine. We have studied two inheritable cysteine mutants of cyclic nucleotide-gated channels that produce achromatopsia, a common form of severe color blindness. By taking advantage of the reactivity of cysteine’s sulfhydryl group, we modified these mutants with chemical reagents that attach moieties with similar chemistries to the wild-type amino acids’ side chains. We show that these modifications restored proper delivery to the cell membrane. Once there, the channels exhibited normal functional properties. This strategy might provide a unique opportunity to assess the chemical nature of membrane protein traffic problems.

An extensive catalog of plasma membrane (PM) protein mutations related to phenotypic diseases is associated with incorrect protein folding and/or localization. These impairments, in addition to dysfunction, frequently promote protein aggregation, which can be detrimental to cells. Here, we review PM protein processing, from protein synthesis in the endoplasmic reticulum to delivery to the PM, stressing the main repercussions of processing failures and their physiological consequences in pathologies, and we summarize the recent proposed therapeutic strategies to rescue misassembled proteins through different types of chaperones and/or small molecule drugs that safeguard protein quality control and regulate proteostasis.

Most membrane proteins are subject to posttranslational glycosylation, which influences protein function, folding, solubility, stability, and trafficking. This modification has been proposed to protect proteins from proteolysis and modify protein-protein interactions. Voltage-activated ion channels are heavily glycosylated, which can result in up to 30% of the mature molecular mass being contributed by glycans. Normally, the functional consequences of glycosylation are assessed by comparing the function of fully glycosylated proteins with those in which glycosylation sites have been mutated or by expressing proteins in model cells lacking glycosylation enzymes. Here, we study the functional consequences of deglycosylation by PNGase F within the same population of voltage-activated potassium (K) channels. We find that removal of sugar moieties has a small, but direct, influence on the voltage-sensing properties and final opening-closing transition of Shaker K channels. Yet, we observe that the interactions of various ligands with different domains of the protein are not affected by deglycosylation. These results imply that the sugar mass attached to the voltage sensor neither represents a cargo for the dynamics of this domain nor imposes obstacles to the access of interacting molecules.