The mother of all endocytosis

Massive endocytosis is initiated by a series of steps that involve a sudden influx of calcium ions, changes in mitochondria, and modification of surface proteins by lipids. A better understanding of this process could lead to new approaches to reducing the tissue damage that is caused by heart attacks

Sperm BerserKers

Human sperm cells rely on an unusual type of potassium ion channel

Calcium release from the nucleus by InsP3 receptor channels

AbstractThe nucleus is surrounded by a double membrane separating it from the cytoplasm. The perinuclear space is continuous with endoplasmic reticulum, and the nuclear outer membrane shares many features with the reticular membrane. We now show that inositol 1,4,5-trisphosphate (InsP3) receptors associated with the ] nucleus release Ca2+ from isolated Xenopus laevis oocyte nuclei. Electrophysiological measurements of the intracellular InsP3 receptor in its native membrane have not been possible on the fine filamentous endoplasmic reticulum. In this paper, we directly measure InsP3-dependent receptor channels in isolated nuclei. The nuclear InsP3 receptor is activated by InsP3 and modulated by Ca2+. The channel is weakly regulated by ATP, is mildly voltage dependent, and has a greater conductance with monovalent cations than with divalent cations

CatSper and Two-Pore channels (version 2019.4) in the IUPHAR/BPS Guide to Pharmacology Database

CatSper channels (CatSper1-4, nomenclature as agreed by NC-IUPHAR [13]) are putative 6TM, voltage-gated, alkalinization-activated calcium permeant channels that are presumed to assemble as a tetramer of α-like subunits and mediate the current ICatSper [21]. In mammals, CatSper subunits are structurally most closely related to individual domains of voltage-activated calcium channels (Cav) [36]. CatSper1 [36], CatSper2 [33] and CatSpers 3 and 4 [25, 19, 32], in common with a putative 2TM auxiliary CatSperβ protein [24] and two putative 1TM associated CatSperγ and CatSperδ proteins [42, 11], are restricted to the testis and localised to the principle piece of sperm tail. The novel cross-species CatSper channel inhibitor, RU1968, has been proposed as a useful tool to aid characterisation of native CatSper channels [37].Two-pore channels (TPCs) are structurally related to CatSpers, CaVs and NaVs. TPCs have a 2x6TM structure with twice the number of TMs of CatSpers and half that of CaVs. There are three animal TPCs (TPC1-TPC3). Humans have TPC1 and TPC2, but not TPC3. TPC1 and TPC2 are localized in endosomes and lysosomes [4]. TPC3 is also found on the plasma membrane and forms a voltage-activated, non-inactivating Na+ channel [5]. All the three TPCs are Na+-selective under whole-cell or whole-organelle patch clamp recording [44, 7, 6]. The channels may also conduct Ca2+ [29]

MCU encodes the pore conducting mitochondrial calcium currents

Mitochondrial calcium (Ca2+) import is a well-described phenomenon regulating cell survival and ATP production. Of multiple pathways allowing such entry, the mitochondrial Ca2+ uniporter is a highly Ca2+-selective channel complex encoded by several recently-discovered genes. However, the identity of the pore-forming subunit remains to be established, since knockdown of all the candidate uniporter genes inhibit Ca2+ uptake in imaging assays, and reconstitution experiments have been equivocal. To definitively identify the channel, we use whole-mitoplast voltage-clamping, the technique that originally established the uniporter as a Ca2+ channel. We show that RNAi-mediated knockdown of the mitochondrial calcium uniporter (MCU) gene reduces mitochondrial Ca2+ current (IMiCa), whereas overexpression increases it. Additionally, a classic feature of IMiCa, its sensitivity to ruthenium red inhibition, can be abolished by a point mutation in the putative pore domain without altering current magnitude. These analyses establish that MCU encodes the pore-forming subunit of the uniporter channel. DOI: http://dx.doi.org/10.7554/eLife.00704.00

Two Separate Interfaces between the Voltage Sensor and Pore Are Required for the Function of Voltage-Dependent K+ Channels

Voltage-dependent K+ (Kv) channels gate open in response to the membrane voltage. To further our understanding of how cell membrane voltage regulates the opening of a Kv channel, we have studied the protein interfaces that attach the voltage-sensor domains to the pore. In the crystal structure, three physical interfaces exist. Only two of these consist of amino acids that are co-evolved across the interface between voltage sensor and pore according to statistical coupling analysis of 360 Kv channel sequences. A first co-evolved interface is formed by the S4-S5 linkers (one from each of four voltage sensors), which form a cuff surrounding the S6-lined pore opening at the intracellular surface. The crystal structure and published mutational studies support the hypothesis that the S4-S5 linkers convert voltage-sensor motions directly into gate opening and closing. A second co-evolved interface forms a small contact surface between S1 of the voltage sensor and the pore helix near the extracellular surface. We demonstrate through mutagenesis that this interface is necessary for the function and/or structure of two different Kv channels. This second interface is well positioned to act as a second anchor point between the voltage sensor and the pore, thus allowing efficient transmission of conformational changes to the pore's gate

Direct recording and molecular identification of the calcium channel of primary cilia

Summary A primary cilium is a solitary slender non-motile protuberance of structured microtubules (9+0) enclosed by plasma membrane1. Housing components of the cell division apparatus between cell divisions, they also serve as specialized compartments for calcium signaling2 and Hedgehog (Hh) signaling pathways3. Specialized sensory cilia such as retinal photoreceptors and olfactory cilia employ diverse ion channels4-7. An ion current has been measured from primary cilia of kidney cells8 but the responsible genes have not been identified. The polycystin proteins (PC, PKD), identified in linkage studies of polycystic kidney disease9, are candidate channels divided into two structural classes: 11-transmembrane (TM) proteins (PKD1, PKD1-L1 and PKD1-L2) remarkable for a large extracellular N-terminus of putative cell adhesion domains and a GPCR proteolytic site, and the 6-TM channel proteins (PKD2, PKD2-L1, PKD2-L2; TRPPs). Evidence suggests that the PKD1s associate with the PKD2s via coiled-coil domains10-12. Here, we employ a transgenic mouse in which only cilia express a fluorophore and employ it to directly record from primary cilia and demonstrate that PKD1-L1 and PKD2-L1 form ion channels at high densities in several cell types. In conjunction with the companion manuscript2, we show that the PKD1-L1/PKD2-L1 heteromeric channel establishes the cilia as a unique calcium compartment within cells that modulates established Hedgehog pathways