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1.A.78 The K+-selective Channel in Endosomes and Lysosomes (KEL) Family 

Organelle K+ conductance studies revealed a major K(+)-selective channel, KEL or TMEM175, on endosomes and lysosomes (Cang et al. 2015). Unlike any of the approximately 80 plasma membrane K+ channels in mammals, TMEM175 has two repeats of 6 TMSs and has no GYG K+ channel sequence signature in a pore (P) loop. Lysosomes lacking TMEM175 exhibit no K+ conductance, have a markedly depolarized Δpsi and little sensitivity to changes in [K+]. These mutants have compromised luminal pH stability and abnormal fusion with autophagosomes during autophagy. Thus, TMEM175 comprises a K+ channel that underlies the molecular mechanism of lysosomal K+ permeability (Cang et al. 2015).

The generalized reaction catalyzed by KEL is:

K+(in the lumen of endosomes and lysosomes) ⇌ K+ (cytoplasm)

References associated with 1.A.78 family:

Cang, C., K. Aranda, Y.J. Seo, B. Gasnier, and D. Ren. (2015). TMEM175 Is an Organelle K+ Channel Regulating Lysosomal Function. Cell 162: 1101-1112. 26317472
Jing, C.C., X.G. Luo, H.G. Cui, F.R. Li, P. Li, E.Z. Jiang, Y. Ren, and H. Pang. (2015). Screening of polymorphisms located in the FGF20 and TMEM175 genes in North Chinese Parkinson''s disease patients. Genet Mol Res 14: 13679-13687. 26535683
Jinn, S., R.E. Drolet, P.E. Cramer, A.H. Wong, D.M. Toolan, C.A. Gretzula, B. Voleti, G. Vassileva, J. Disa, M. Tadin-Strapps, and D.J. Stone. (2017). TMEM175 deficiency impairs lysosomal and mitochondrial function and increases α-synuclein aggregation. Proc. Natl. Acad. Sci. USA. [Epub: Ahead of Print] 28193887
Lee, C., J. Guo, W. Zeng, S. Kim, J. She, C. Cang, D. Ren, and Y. Jiang. (2017). The lysosomal potassium channel TMEM175 adopts a novel tetrameric architecture. Nature 547: 472-475. 28723891