MICU2, a Paralog of MICU1, Resides within the Mitochondrial Uniporter Complex to Regulate Calcium Handling

Mitochondrial calcium uptake is present in nearly all vertebrate tissues and is believed to be critical in shaping calcium signaling, regulating ATP synthesis and controlling cell death. Calcium uptake occurs through a channel called the uniporter that resides in the inner mitochondrial membrane. Recently, we used comparative genomics to identify MICU1 and MCU as the key regulatory and putative pore-forming subunits of this channel, respectively. Using bioinformatics, we now report that the human genome encodes two additional paralogs of MICU1, which we call MICU2 and MICU3, each of which likely arose by gene duplication and exhibits distinct patterns of organ expression. We demonstrate that MICU1 and MICU2 are expressed in HeLa and HEK293T cells, and provide multiple lines of biochemical evidence that MCU, MICU1 and MICU2 reside within a complex and cross-stabilize each other's protein expression in a cell-type dependent manner. Using in vivo RNAi technology to silence MICU1, MICU2 or both proteins in mouse liver, we observe an additive impairment in calcium handling without adversely impacting mitochondrial respiration or membrane potential. The results identify MICU2 as a new component of the uniporter complex that may contribute to the tissue-specific regulation of this channel.National Institutes of Health (U.S.) (GM0077465)National Institutes of Health (U.S.) (DK080261

The Mitochondrial Ca(2+) Uniporter: Structure, Function, and Pharmacology.

Mitochondrial Ca(2+) uptake is crucial for an array of cellular functions while an imbalance can elicit cell death. In this chapter, we briefly reviewed the various modes of mitochondrial Ca(2+) uptake and our current understanding of mitochondrial Ca(2+) homeostasis in regards to cell physiology and pathophysiology. Further, this chapter focuses on the molecular identities, intracellular regulators as well as the pharmacology of mitochondrial Ca(2+) uniporter complex

Divalent Metal Ions Tune the Self-Splicing Reaction of the Yeast Mitochondrial Group II Intron Sc.ai5γ

Group II introns are large ribozymes, consisting of six functionally distinct domains that assemble in the presence of Mg2+ to the active structure catalyzing a variety of reactions. The first step of intron splicing is well characterized by a Michaelis–Menten-type cleavage reaction using a two-piece group II intron: the substrate RNA, the 5′-exon covalently linked to domains 1, 2, and 3, is cleaved upon addition of domain 5 acting as a catalyst. Here we investigate the effect of Ca2+, Mn2+, Ni2+, Zn2+, Cd2+, Pb2+, and [Co(NH3)6]3+ on the first step of splicing of the Saccharomyces cerevisiae mitochondrial group II intron Sc.ai5γ. We find that this group II intron is very sensitive to the presence of divalent metal ions other than Mg2+. For example, the presence of only 5% Ca2+ relative to Mg2+ results in a decrease in the maximal turnover rate k cat by 50%. Ca2+ thereby has a twofold effect: this metal ion interferes initially with folding, but then also competes directly with Mg2+ in the folded state, the latter being indicative of at least one specific Ca2+ binding pocket interfering directly with catalysis. Similar results are obtained with Mn2+, Cd2+, and [Co(NH3)6]3+. Ni2+ is a much more powerful inhibitor and the presence of either Zn2+ or Pb2+ leads to rapid degradation of the RNA. These results show a surprising sensitivity of such a large multidomain RNA on trace amounts of cations other than Mg2+ and raises the question of biological relevance at least in the case of Ca2+

Last word on viewpoint: the cardiac contraction cycle: is Ca²⁺ going local?

No abstract available