Crystal structure of MICU2 and comparison with MICU1 reveal insights into the uniporter gating mechanism

Journal Article · 12 February 2019 · Proceedings of the National Academy of Sciences of the United States of America

DOI: https://doi.org/10.1073/pnas.1817759116 · OSTI ID:1558321

Kamer, Kimberli J.  ^[1]; Jiang, Wei ^[2]; Kaushik, Virendar K. ^[2]; Mootha, Vamsi K. ^[3]; Grabarek, Zenon ^[4]

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1. Harvard Univ., Cambridge, MA (United States); Harvard Medical School, Boston, MA (United States)
2. Broad Inst., Cambridge, MA (United States)
3. Harvard Medical School, Boston, MA (United States); Broad Inst., Cambridge, MA (United States)
4. Harvard Medical School, Boston, MA (United States)

The mitochondrial uniporter is a Ca²⁺-channel complex resident within the organelle’s inner membrane. In mammalian cells the uniporter’s activity is regulated by Ca²⁺ due to concerted action of MICU1 and MICU2, two paralogous, but functionally distinct, EF-hand Ca²⁺-binding proteins. In this paper, we present the X-ray structure of the apo form of Mus musculus MICU2 at 2.5-Å resolution. The core structure of MICU2 is very similar to that of MICU1. It consists of two lobes, each containing one canonical Ca²⁺-binding EF-hand (EF1, EF4) and one structural EF-hand (EF2, EF3). Two molecules of MICU2 form a symmetrical dimer stabilized by highly conserved hydrophobic contacts between exposed residues of EF1 of one monomer and EF3 of another. Similar interactions stabilize MICU1 dimers, allowing exchange between homo- and heterodimers. The tight EF1–EF3 interface likely accounts for the structural and functional coupling between the Ca²⁺-binding sites in MICU1, MICU2, and their complex that leads to the previously reported Ca²⁺-binding cooperativity and dominant negative effect of mutation of the Ca²⁺-binding sites in either protein. The N- and C-terminal segments of the two proteins are distinctly different. In MICU2 the C-terminal helix is significantly longer than in MICU1, and it adopts a more rigid structure. MICU2’s C-terminal helix is dispensable in vitro for its interaction with MICU1 but required for MICU2’s function in cells. We propose that in the MICU1–MICU2 oligomeric complex the C-terminal helices of both proteins form a central semiautonomous assembly which contributes to the gating mechanism of the uniporter.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States). Advanced Photon Source (APS); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
• Sponsoring Organization: Calico; National Institutes of Health (NIH); USDOE Office of Science (SC)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1558321
• Journal Information: Proceedings of the National Academy of Sciences of the United States of America, Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Issue: 9 Vol. 116; ISSN 0027-8424
• Publisher: National Academy of SciencesCopyright Statement
• Country of Publication: United States
• Language: ENGLISH