High-conductance magnesium-selective channel that mediates the influx of magnesium into the mitochondrial matrix. Essential for the splicing of mRNA group II introns in mitochondria by affecting mitochondrial magnesium concentrations, which are critical for group II intron splicing. It also suppresses a variety of mitochondrial intron mutations and its absence may disturb the assembly of mitochondrial membrane complexes. Homopentamer. Forms homooligomers. Interacts with MFM1. Belongs to the CorA metal ion transporter (MIT) (TC 1.A.35) family.