| Structural highlights
Function
[MICU2_MOUSE] Key regulator of mitochondrial calcium uniporter (MCU) required to limit calcium uptake by MCU when cytoplasmic calcium is low (PubMed:23409044, PubMed:24560927). MICU1 and MICU2 form a disulfide-linked heterodimer that stimulate and inhibit MCU activity, depending on the concentration of calcium (PubMed:24560927). MICU2 acts as a gatekeeper of MCU that senses calcium level via its EF-hand domains: prevents channel opening at resting Ca(2+), avoiding energy dissipation and cell-death triggering (PubMed:24560927).[1] [2]
Publication Abstract from PubMed
The mitochondrial uniporter is a Ca(2+)-channel complex resident within the organelle's inner membrane. In mammalian cells the uniporter's activity is regulated by Ca(2+) due to concerted action of MICU1 and MICU2, two paralogous, but functionally distinct, EF-hand Ca(2+)-binding proteins. Here we present the X-ray structure of the apo form of Mus musculus MICU2 at 2.5-A resolution. The core structure of MICU2 is very similar to that of MICU1. It consists of two lobes, each containing one canonical Ca(2+)-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 Ca(2+)-binding sites in MICU1, MICU2, and their complex that leads to the previously reported Ca(2+)-binding cooperativity and dominant negative effect of mutation of the Ca(2+)-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.
Crystal structure of MICU2 and comparison with MICU1 reveal insights into the uniporter gating mechanism.,Kamer KJ, Jiang W, Kaushik VK, Mootha VK, Grabarek Z Proc Natl Acad Sci U S A. 2019 Feb 12. pii: 1817759116. doi:, 10.1073/pnas.1817759116. PMID:30755530[3]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Plovanich M, Bogorad RL, Sancak Y, Kamer KJ, Strittmatter L, Li AA, Girgis HS, Kuchimanchi S, De Groot J, Speciner L, Taneja N, Oshea J, Koteliansky V, Mootha VK. MICU2, a paralog of MICU1, resides within the mitochondrial uniporter complex to regulate calcium handling. PLoS One. 2013;8(2):e55785. doi: 10.1371/journal.pone.0055785. Epub 2013 Feb 7. PMID:23409044 doi:http://dx.doi.org/10.1371/journal.pone.0055785
- ↑ Patron M, Checchetto V, Raffaello A, Teardo E, Vecellio Reane D, Mantoan M, Granatiero V, Szabo I, De Stefani D, Rizzuto R. MICU1 and MICU2 finely tune the mitochondrial Ca2+ uniporter by exerting opposite effects on MCU activity. Mol Cell. 2014 Mar 6;53(5):726-37. doi: 10.1016/j.molcel.2014.01.013. Epub 2014, Feb 20. PMID:24560927 doi:http://dx.doi.org/10.1016/j.molcel.2014.01.013
- ↑ Kamer KJ, Jiang W, Kaushik VK, Mootha VK, Grabarek Z. Crystal structure of MICU2 and comparison with MICU1 reveal insights into the uniporter gating mechanism. Proc Natl Acad Sci U S A. 2019 Feb 12. pii: 1817759116. doi:, 10.1073/pnas.1817759116. PMID:30755530 doi:http://dx.doi.org/10.1073/pnas.1817759116
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