Strünker Timo

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Strünker
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Timo
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  • Article
    Author correction: the solute carrier SLC9C1 is a Na(+)/H(+)-exchanger gated by an S4-type voltage-sensor and cyclic-nucleotide binding
    (Nature Research, 2020-08-19) Windler, Florian ; Bönigk, Wolfgang ; Körschen, Heinz Gerd ; Grahn, Elena ; Strünker, Timo ; Seifert, Reinhard ; Kaupp, U. Benjamin
  • Article
    The solute carrier SLC9C1 is a Na+/H+-exchanger gated by an S4-type voltage-sensor and cyclic-nucleotide binding
    (Nature Publishing Group, 2018-07-18) Windler, Florian ; Bönigk, Wolfgang ; Körschen, Heinz Gerd ; Grahn, Elena ; Strünker, Timo ; Seifert, Reinhard ; Kaupp, U. Benjamin
    Voltage-sensing (VSD) and cyclic nucleotide-binding domains (CNBD) gate ion channels for rapid electrical signaling. By contrast, solute carriers (SLCs) that passively redistribute substrates are gated by their substrates themselves. Here, we study the orphan sperm-specific solute carriers SLC9C1 that feature a unique tripartite structure: an exchanger domain, a VSD, and a CNBD. Voltage-clamp fluorimetry shows that SLC9C1 is a genuine Na+/H+ exchanger gated by voltage. The cellular messenger cAMP shifts the voltage range of activation. Mutations in the transport domain, the VSD, or the CNBD strongly affect Na+/H+ exchange, voltage gating, or cAMP sensitivity, respectively. Our results establish SLC9C1 as a phylogenetic chimaera that combines the ion-exchange mechanism of solute carriers with the gating mechanism of ion channels. Classic SLCs slowly readjust changes in the intra- and extracellular milieu, whereas voltage gating endows the Na+/H+ exchanger with the ability to produce a rapid pH response that enables downstream signaling events.
  • Article
    Absolute proteomic quantification reveals design principles of sperm flagellar chemosensation
    (EMBO Press, 2019-12-27) Trotschel, Christian ; Hamzeh, Hussein ; Alvarez, Luis ; Pascal, René ; Lavryk, Fedir ; Bönigk, Wolfgang ; Körschen, Heinz Gerd ; Müller, Astrid ; Poetsch, Ansgar ; Rennhack, Andreas ; Gui, Long ; Nicastro, Daniela ; Strünker, Timo ; Seifert, Reinhard ; Kaupp, U. Benjamin
    Cilia serve as cellular antennae that translate sensory information into physiological responses. In the sperm flagellum, a single chemoattractant molecule can trigger a Ca2+ rise that controls motility. The mechanisms underlying such ultra‐sensitivity are ill‐defined. Here, we determine by mass spectrometry the copy number of nineteen chemosensory signaling proteins in sperm flagella from the sea urchin Arbacia punctulata. Proteins are up to 1,000‐fold more abundant than the free cellular messengers cAMP, cGMP, H+, and Ca2+. Opto‐chemical techniques show that high protein concentrations kinetically compartmentalize the flagellum: Within milliseconds, cGMP is relayed from the receptor guanylate cyclase to a cGMP‐gated channel that serves as a perfect chemo‐electrical transducer. cGMP is rapidly hydrolyzed, possibly via “substrate channeling” from the channel to the phosphodiesterase PDE5. The channel/PDE5 tandem encodes cGMP turnover rates rather than concentrations. The rate‐detection mechanism allows continuous stimulus sampling over a wide dynamic range. The textbook notion of signal amplification—few enzyme molecules process many messenger molecules—does not hold for sperm flagella. Instead, high protein concentrations ascertain messenger detection. Similar mechanisms may occur in other small compartments like primary cilia or dendritic spines.