KCNK13 Membrane Protein Introduction

Introduction of KCNK13

Potassium channel subfamily K member 13 (KCNK13), also known as tandem pore domain halothane-inhibited potassium channel THIK-1 and K_2P13.1, is encoded by gene KCNK13. KCNK13 is assigned to chromosomal region 14q24.1-14q24.3. Sharing 58% sequence homology with KCNK12 (THIK-2), KCNK13 also belongs to the family of tandem pore domain potassium (K_2P) channels, characterized with four transmembrane segments (M1-M4) and two typical pore-forming regions (P1 and P2) including the K⁺ selectivity filter consensus sequence and a large extracellular loop between M1 and P1. In human kidney, KCNK13 is mainly expressed in the proximal tubule (PT), thick ascending limb (TAL), and cortical collecting duct (CCD). It is compelling that KCNK13 carries a caspase recognition sequence in its cytoplasmic region.

Function of KCNK13 Membrane Protein

Unlike KCNK12, a ‘silent’ channel of K_2P family, KCNK13 can produce background K⁺ currents by itself, and that is inhibited by halothane and insensitive to extracellular pH variations. Beyond the function of setting the resting membrane potential and thus regulating cell excitability, the background K⁺ channels can regulate cell function under various physiological and pathophysiological conditions, via targeting to multiple intracellular and extracellular biological signals. KCNK13 combines with KCNK12 to form active heteromeric channels and tandem-KCNK13-KCNK12 distributes at the plasma membrane, whereas tandem-KCNK12-KCNK12 is mainly detected in the endoplasmic reticulum, indicating that KCNK13 can mask the endoplasmic reticulum retention/retrieval motif of KCNK12. It is documented that whole-cell KCNK13 current can be inhibited by halothane and activated by arachidonic acid. It has been identified that KCNK13 is a novel substrate of caspase-8, which can cleave an evolutionarily conserved sequence in the intracellular region of KCNK13. Overexpression of KCNK13 will accelerate cell shrinkage in response to apoptotic stimuli. Furthermore, a truncated KCNK13 mutant lacking the intracellular region will decrease cell volume without apoptotic stimulation and excessively promote the irregular development of Xenopus embryos.

Fig.1 The transmembrane topology, crystal structure and dendrogram of human K2P channels. (Feliciangeli, 2015)

Application of KCNK13 Membrane Protein in Literature

1. Sakamaki K., et al. Dysregulation of a potassium channel, THIK-1, targeted by caspase-8 accelerates cell shrinkage. Biochimica et Biophysica Acta (BBA)-Molecular Cell Research. 2016, 1863(11): 2766-2783. PubMed ID: 27566292
   
   

   In this article, the authors identified that THIK-1 was a novel caspase-8 substrate, which could cleave an evolutionarily conserved sequence in the intracellular region of THIK-1. Fluctuating expression of THIK-1 would affect cell volume during apoptosis and underexpression of THIK-1 resulted in the delay of K⁺ efflux in dying cells.

2. Blin S., et al. Tandem pore domain halothane-inhibited K⁺ channel subunits THIK1 and THIK2 assemble and form active channels. Journal of Biological Chemistry. 2014, 289(41): 28202-28212. PubMed ID: 25148687
   
   

   This article revealed that THIK1 and THIK2 could assemble to form active channels. Moreover, Tandem-THIK1-THIK2 could induce K⁺ currents of amplitude similar to Tandem-THIK1-THIK1 but with a noticeable difference in the current kinetics.

3. Kang D., et al. THIK-1 (K_2P13.1) is a small-conductance background K⁺ channel in rat trigeminal ganglion neurons. Pflügers Archiv-European Journal of Physiology. 2014, 466(7): 1289-1300. PubMed ID: 24081450
   
   

   This article demonstrated that THIK-1 was functionally expressed in trigeminal ganglion (TG) neurons and could produce a small conductance (~5-pS) channel contributing to the background K⁺ conductance.

4. Lazarenko R.M., et al. Anesthetic activation of central respiratory chemoreceptor neurons involves inhibition of a THIK-1-like background K⁺ current. Journal of Neuroscience. 2010, 30(27): 9324-9334. PubMed ID: 20610767
   
   

   The authors demonstrated that isoflurane caused activation of RTN neurons, which was CO₂/pH-sensitive and located in the retrotrapezoid nucleus (RTN) of the rodent brainstem. In this process, inhibition of THIK-1-like background K⁺ current was essential, which may contribute to maintaining respiratory motor activity under immobilizing anesthetic conditions.

5. Rajan S., et al. THIK-1 and THIK-2, a novel subfamily of tandem pore domain K⁺ channels. Journal of Biological Chemistry. 2001, 276(10): 7302-7311. PubMed ID: 11060316
   
   

   The authors described the cloning of the first two members of a novel subfamily of 2P K⁺ channels (THIK-1 and THIK-2) from rat brain, and they studied the distribution of these channels. In rats, THIK-1 was expressed ubiquitously, while THIK-2 expression was found in several tissues including brain and kidney.

6. Feliciangeli S., et al. The family of K_2P channels: salient structural and functional properties. The Journal of physiology. 2015, 593(12): 2587-2603. PubMed ID: 25530075
   
   

   The review gathered massive data and gave a synthetic view of the most noticeable features of the K_2P channels which were central players in many processes, including ion homeostasis, hormone secretion, cell development, and excitability.

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Reference

1. Feliciangeli S, et al. (2015). The family of K_2P channels: salient structural and functional properties. The Journal of physiology. 593(12): 2587-2603.

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