The molecular appearance of native TRPM7 channel complexes identified by high-resolution proteomics

The transient receptor potential melastatin-subfamily member 7 (TRPM7) is a ubiquitously expressed membrane protein consisting of ion channel and protein kinase domains. TRPM7 plays a fundamental role in the cellular uptake of divalent cations such as Zn2+, Mg2+, and Ca2+, and thus shapes cellular excitability, plasticity, and metabolic activity. The molecular appearance and operation of TRPM7 channels in native tissues have remained unresolved. Here, we investigated the subunit composition of endogenous TRPM7 channels in rodent brain by multi-epitope affinity purification and high-resolution quantitative mass spectrometry (MS) analysis. We found that native TRPM7 channels are high-molecular-weight multi-protein complexes that contain the putative metal transporter proteins CNNM1-4 and a small G-protein ADP-ribosylation factor-like protein 15 (ARL15). Heterologous reconstitution experiments confirmed the formation of TRPM7/CNNM/ARL15 ternary complexes and indicated that complex formation effectively and specifically impacts TRPM7 activity. These results open up new avenues towards a mechanistic understanding of the cellular regulation and function of TRPM7 channels

Subunit composition, molecular environment, and activation of native TRPC channels encoded by their interactomes.

peer reviewedIn the mammalian brain TRPC channels, a family of Ca2+-permeable cation channels, are involved in a variety of processes from neuronal growth and synapse formation to transmitter release, synaptic transmission and plasticity. The molecular appearance and operation of native TRPC channels, however, remained poorly understood. Here, we used high-resolution proteomics to show that TRPC channels in the rodent brain are macro-molecular complexes of more than 1 MDa in size that result from the co-assembly of the tetrameric channel core with an ensemble of interacting proteins (interactome). The core(s) of TRPC1-, C4-, and C5-containing channels are mostly heteromers with defined stoichiometries for each subtype, whereas TRPC3, C6, and C7 preferentially form homomers. In addition, TRPC1/C4/C5 channels may co-assemble with the metabotropic glutamate receptor mGluR1, thus guaranteeing both specificity and reliability of channel activation via the phospholipase-Ca2+ pathway. Our results unveil the subunit composition of native TRPC channels and resolve the molecular details underlying their activation

A structural model for K2P potassium channels based on 23 pairs of interacting sites and continuum electrostatics

K2PØ, the two-pore domain potassium background channel that determines cardiac rhythm in Drosophila melanogaster, and its homologues that establish excitable membrane activity in mammals are of unknown structure. K2P subunits have two pore domains flanked by transmembrane (TM) spans: TM1-P1-TM2-TM3-P2-TM4. To establish spatial relationships in K2PØ, we identified pairs of sites that display electrostatic compensation. Channels silenced by the addition of a charge in pore loop 1 (P1) or P2 were restored to function by countercharges at specific second sites. A three-dimensional homology model was determined using the crystal structure of KV1.2, effects of K2PØ mutations to establish alignment, and compensatory charge–charge pairs. The model was refined and validated by continuum electrostatic free energy calculations and covalent linkage of introduced cysteines. K2P channels use two subunits arranged so that the P1 and P2 loops contribute to one pore, identical P loops face each other diagonally across the pore, and the channel complex has bilateral symmetry with a fourfold symmetric selectivity filter

Klonierung und Charakterisierung von Säugerhomologen des für die Muskelkontraktion relevanten Unc-93 aus Caenorhabditis elegans

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Characterization of Pellino2, a substrate of IRAK1 and IRAK4

AbstractInterleukin-1 (IL-1) receptor-associated kinases (IRAKs) are central components of Toll/IL-1 receptor (TIR) signaling pathways. In an attempt to discover novel signal transducers in TIR signaling, we identified human Pellino2 as an interaction partner of IRAK4. Pellino2 interacts with kinase-active as well as kinase-inactive IRAK1 and IRAK4. Furthermore, Pellino2 is one of the first substrates identified for IRAK1 and IRAK4. Functional studies using overexpression or RNAi knock-down of Pellino2 suggest a role of Pellino2 as a scaffolding protein similar to Pellino1. However, unlike Pellino1, Pellino2 does not seem to activate a specific transcription factor, but links TIR signaling to basic cellular processes

Real-life use of onabotulinumtoxinA reduces healthcare resource utilization in individuals with chronic migraine: the REPOSE study

Background!#!Chronic migraine (CM) is associated with substantial economic burden. Real-world data suggests that onabotulinumtoxinA treatment for CM reduces healthcare resource utilisation (HRU) and related costs.!##!Methods!#!REPOSE was a 2-year prospective, multicentre, non-interventional, observational study to describe the real-world use of onabotulinumtoxinA in adult patients with CM. This analysis examined the impact of onabotulinumtoxinA on HRU. Patients received onabotulinumtoxinA treatment approximately every 12 weeks according to their physicians' discretion, guided by the summary of product characteristics (SPC) and PREEMPT injection paradigm. HRU outcome measures were collected at baseline and all administration visits and included headache-related hospitalizations and healthcare professional (HCP) visits. Health economic data, including family doctor and specialist visits, inpatient treatment for headache, acupuncture, technical diagnostics, use of nonpharmacologic remedies, and work productivity were also collected for patients enrolled at German study centres.!##!Results!#!Overall, 641 patients were enrolled at 78 study centres across 7 countries (Germany, UK, Italy, Spain, Norway, Sweden, and Russia), 633 received ≥1 onabotulinumtoxinA dose, and 128 completed the 2-year study. Patients were, on average, aged 45 years, 85% were female, and 60% (n = 377) were from Germany. At the end of the 2-year observation period, significantly fewer patients reported headache-related hospitalizations (p < 0.02) and HCP visits (p < 0.001) within the past 3 months than in the 3 months before baseline. In the German population, reductions were observed across all health services at all follow-up visits compared with baseline. The percentage of patients who saw a family doctor decreased from 41.7% at baseline to 13.5% at administration visit 8 and visits to a medical specialist decreased from 61.7% to 5.2% of patients. Inpatient acute treatment and technical diagnostics declined from 6.4% and 19.7% of patients at baseline to 0.0% and 1.0% at administration 8, respectively. The use of nonpharmacologic remedies and medication for the acute treatment of migraine also decreased with continued onabotulinumtoxinA treatment. Work incapacity, disability, absenteeism, and impaired performance at school/work improved with onabotulinumtoxinA treatment for CM over the 2-year observation period.!##!Conclusions!#!Real-world evidence from REPOSE demonstrates that onabotulinumtoxinA treatment is associated with decreased HRU and supports the long-term benefits associated with the use of onabotulinumtoxinA for CM in clinical practice.!##!Trial registration!#!NCT01686581 . Name of registry: ClinicalTrials.gov. URL of registry: Date of retrospective registration: September 18, 2012. Date of enrolment of first patient: July 23, 2012

A structural model for K2P potassium channels based on 23 pairs of interacting sites and continuum electrostatics.

K(2P)Ø, the two-pore domain potassium background channel that determines cardiac rhythm in Drosophila melanogaster, and its homologues that establish excitable membrane activity in mammals are of unknown structure. K(2P) subunits have two pore domains flanked by transmembrane (TM) spans: TM1-P1-TM2-TM3-P2-TM4. To establish spatial relationships in K(2P)Ø, we identified pairs of sites that display electrostatic compensation. Channels silenced by the addition of a charge in pore loop 1 (P1) or P2 were restored to function by countercharges at specific second sites. A three-dimensional homology model was determined using the crystal structure of K(V)1.2, effects of K(2P)Ø mutations to establish alignment, and compensatory charge-charge pairs. The model was refined and validated by continuum electrostatic free energy calculations and covalent linkage of introduced cysteines. K(2P) channels use two subunits arranged so that the P1 and P2 loops contribute to one pore, identical P loops face each other diagonally across the pore, and the channel complex has bilateral symmetry with a fourfold symmetric selectivity filter

One SUMO is sufficient to silence the dimeric potassium channel K2P1.

Small ubiquitin modifier 1 (SUMO1) is shown to regulate K2P1 background channels in the plasma membrane (PM) of live mammalian cells. Confocal microscopy reveals native SUMO1, SAE1, and Ubc9 (the enzymes that activate and conjugate SUMO1) at PM where SUMO1 and expressed human K2P1 are demonstrated to colocalize. Silent K2P1 channels in excised PM patches are activated by SUMO isopeptidase (SENP1) and resilenced by SUMO1. K2P1-Lys274 is crucial: when mutated to Gln, Arg, Glu, Asp, Cys, or Ala, the channels are constitutively active and insensitive to SUMO1 and SENP1. Tandem mass spectrometry confirms conjugation of SUMO1 to the epsilon-amino group of Lys274 in vitro. FRET microscopy shows that assembly of K2P1 and SUMO1 requires Lys274. Single-particle TIRF microscopy shows that wild-type channels in PM have two K2P1 subunits and assemble with two SUMO1 monomers. Although channels engineered with one Lys274 site carry just one SUMO1 they are activated and silenced by SENP1 and SUMO1 like wild-type channels

Exocytotic mechanism studied by truncated and zero layer mutants of the C-terminus of SNAP-25

The highly conserved SNARE proteins, SNAP-25, syntaxin and synaptobrevin, form a tight ternary complex, which is essential for exocytosis. Crystallization of this complex revealed a four-helix bundle with an unusual hydrophilic layer (zero layer) in its center. In order to evaluate the role of this layer in different kinetic components of secretion, we used the Semliki Forest virus (SFV) system to infect adrenal chromaffin cells with SNAP-25 Q174L, a point mutant in the zero layer. Using combined flash photolysis of caged calcium and membrane capacitance measurements, we investigated its effect on the exocytotic burst and sustained phase of exocytosis with high time resolution. Cells expressing SNAP-25 Q174L displayed a selective reduction in the sustained phase, while the two components of the exocytotic burst remained unaffected. Furthermore, the exocytotic response to the second flash was significantly reduced, indicating a decrease in refilling kinetics. We therefore conclude that the zero layer is critical for the formation of SNARE complexes, but that it plays no role in the dynamic equilibrium between the two exocytosis-competent vesicle pools