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Structure. 2019 May 14. pii: S0969-2126(19)30161-3. doi: 10.1016/j.str.2019.04.016. [Epub ahead of print]

Structure of the Human TRPML2 Ion Channel Extracytosolic/Lumenal Domain.

Author information

1
Institute for Pharmacy and Biochemistry, Johannes Gutenberg-Universität Mainz, 55128 Mainz, Germany; Center for Biomolecular Magnetic Resonance (BMRZ), Goethe-Universität, 60438 Frankfurt am Main, Germany.
2
Institute for Pharmacy and Biochemistry, Johannes Gutenberg-Universität Mainz, 55128 Mainz, Germany.
3
Institute for Physical Chemistry, Goethe-Universität, 60438 Frankfurt am Main, Germany.
4
Synchrotron Crystallography Team, EMBL Grenoble Outstation, 38042 Grenoble, France.
5
Rudolf Virchow Centre for Experimental Biomedicine, Universität Würzburg, 97080 Würzburg, Germany.
6
Institute for Pharmacy and Biochemistry, Johannes Gutenberg-Universität Mainz, 55128 Mainz, Germany; Center for Biomolecular Magnetic Resonance (BMRZ), Goethe-Universität, 60438 Frankfurt am Main, Germany. Electronic address: u.hellmich@uni-mainz.de.

Abstract

TRPML2 is the least structurally characterized mammalian transient receptor potential mucolipin ion channel. The TRPML family hallmark is a large extracytosolic/lumenal domain (ELD) between transmembrane helices S1 and S2. We present crystal structures of the tetrameric human TRPML2 ELD at pH 6.5 (2.0 Å) and 4.5 (2.95 Å), corresponding to the pH values in recycling endosomes and lysosomes. Isothermal titration calorimetry shows Ca2+ binding to the highly acidic central pre-pore loop which is abrogated at low pH, in line with a pH-dependent channel regulation model. Small angle X-ray scattering confirms the ELD dimensions in solution. Changes in pH or Ca2+ concentration do not affect the protein's secondary structure, but can influence ELD oligomer integrity according to native mass spectrometry. Our data thus complete the set of high-resolution views of human TRPML channel ELDs and reveal some structural responses to the conditions the TRPML2 ELD encounters as the channel traffics through the endolysosomal system.

KEYWORDS:

Ca(2+) and pH regulation; SAXS; TRP channel; TRPML; X-ray crystallography; isothermal titration calorimetry; mucolipin; native mass spectrometry; polycystin-mucolipin domain; pre-pore loop

PMID:
31178222
DOI:
10.1016/j.str.2019.04.016

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