High‐affinity cooperative Ca2+ binding by MICU1–MICU2 serves as an on–off switch for the uniporter. (14th June 2017)

• Record Type: Journal Article
• Authors: Kamer, Kimberli J; Grabarek, Zenon; Mootha, Vamsi K
• Is Part Of: EMBO reports. Volume 18:Number 8(2017)
• Page Start: 1397
• Page End: 1411
• Publication Date: 2017-06-14
• Subjects: calcium binding -- cardiolipin -- EF hand -- mitochondria -- peripheral membrane; Molecular biology -- Periodicals; Molecular Biology -- Periodicals; Molecular biology; Periodicals; 572.8
• DOI: 10.15252/embr.201643748
• Languages: English
• ISSNs: 1469-221X

Abstract

Abstract: The mitochondrial calcium uniporter is a Ca 2+ ‐activated Ca 2+ channel that is essential for dynamic modulation of mitochondrial function in response to cellular Ca 2+ 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 Ca 2+ . We reconstitute the MICU1–MICU2 heterodimer and demonstrate that it binds Ca 2+ cooperatively with high affinity. We discover that both MICU1 and MICU2 exhibit affinity for the mitochondria‐specific lipid cardiolipin. We determine the minimum Ca 2+ concentration required for disinhibition of the uniporter in permeabilized cells and report a close match with the Ca 2+ ‐binding affinity of MICU1–MICU2. We conclude that cooperative, high‐affinity interaction of the MICU1–MICU2 complex with Ca 2+ serves as an on–off switch, leading to a tightly controlled channel, capable of responding directly to cytosolic Ca 2+ signals. Synopsis: The MICU1–MICU2 heterodimer binds Ca 2+ cooperatively with high affinity, which sets a sharp threshold for the uniporter, and allows direct response to cytosolic Ca 2+ signals. Interaction with cardiolipin facilitates tethering of MICU1–MICU2 to the inner membrane. MICU1 and MICU2 form a heterodimer, which binds Ca 2+ with 620 nM affinity. MICU1–MICU2 Ca 2+ binding determines the threshold of the mitochondrial uniporter. MICU1 and MICU2 bind cardiolipin irrespective of Ca 2+, tethering the complex to the inner membrane. Abstract : The MICU1–MICU2 heterodimer binds Ca 2+ cooperatively with high affinity, which sets a sharp threshold for the uniporter, and allows direct response to cytosolic Ca 2+ signals. Interaction with cardiolipin facilitates tethering of MICU1–MICU2 to the inner membrane.