High-affinity cooperative Ca 2+ binding by MICU1-MICU2 serves as an on-off switch for the uniporter

EMBO Rep. 2017 Aug;18(8):1397-1411. doi: 10.15252/embr.201643748. Epub 2017 Jun 14.

Abstract

The mitochondrial calcium uniporter is a Ca2+-activated Ca2+ channel that is essential for dynamic modulation of mitochondrial function in response to cellular Ca2+ signals. It is regulated by two paralogous EF-hand proteins-MICU1 and MICU2, but the mechanism is unknown. Here, we demonstrate that both MICU1 and MICU2 are stabilized by Ca2+ We reconstitute the MICU1-MICU2 heterodimer and demonstrate that it binds Ca2+ cooperatively with high affinity. We discover that both MICU1 and MICU2 exhibit affinity for the mitochondria-specific lipid cardiolipin. We determine the minimum Ca2+ concentration required for disinhibition of the uniporter in permeabilized cells and report a close match with the Ca2+-binding affinity of MICU1-MICU2. We conclude that cooperative, high-affinity interaction of the MICU1-MICU2 complex with Ca2+ serves as an on-off switch, leading to a tightly controlled channel, capable of responding directly to cytosolic Ca2+ signals.

Keywords: EF hand; calcium binding; cardiolipin; mitochondria; peripheral membrane.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, N.I.H., Extramural

MeSH terms

  • Calcium / metabolism*
  • Calcium Channels / metabolism*
  • Calcium-Binding Proteins / metabolism*
  • Cardiolipins / metabolism
  • Cation Transport Proteins / metabolism*
  • Cytosol / metabolism
  • EF Hand Motifs / physiology
  • HEK293 Cells
  • HeLa Cells
  • Humans
  • Membrane Potential, Mitochondrial
  • Mitochondria / metabolism
  • Mitochondrial Membrane Transport Proteins / metabolism*

Substances

  • Calcium Channels
  • Calcium-Binding Proteins
  • Cardiolipins
  • Cation Transport Proteins
  • MICU1 protein, human
  • MICU2 protein, human
  • Mitochondrial Membrane Transport Proteins
  • mitochondrial calcium uniporter
  • Calcium