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Publication Abstract from PubMed

The TMEM175 family constitutes recently discovered K(+) channels that are important for autophagosome turnover and lysosomal pH regulation and are associated with the early onset of Parkinson Disease. TMEM175 channels lack a P-loop selectivity filter, a hallmark of all known K(+) channels, raising the question how selectivity is achieved. Here, we report the X-ray structure of a closed bacterial TMEM175 channel in complex with a nanobody fusion-protein disclosing bound K(+) ions. Our analysis revealed that a highly conserved layer of threonine residues in the pore conveys a basal K(+) selectivity. An additional layer comprising two serines in human TMEM175 increases selectivity further and renders this channel sensitive to 4-aminopyridine and Zn(2+). Our findings suggest that large hydrophobic side chains occlude the pore, forming a physical gate, and that channel opening by iris-like motions simultaneously relocates the gate and exposes the otherwise concealed selectivity filter to the pore lumen.

Structural basis for ion selectivity in TMEM175 K(+) channels.,Brunner JD, Jakob RP, Schulze T, Neldner Y, Moroni A, Thiel G, Maier T, Schenck S Elife. 2020 Apr 8;9. pii: 53683. doi: 10.7554/eLife.53683. PMID:32267231^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.