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)