TMBIM5 is a Ca2+ channel in the inner mitochondrial membrane

线粒体的许多作用与它们吸收Ca2+的能力有关。线粒体Ca2+摄取的主要驱动力是穿过线粒体内膜的负膜电位。介导向内Ca2+电流的主要通道是线粒体Ca2+单转运蛋白（MCU），这是一种位于线粒体内膜的蛋白质。尽管有这种假定的重要性，但在小鼠中敲除MCU只显示出轻微的生理缺陷，这表明还有未知的备用系统。该项目专注于线粒体Ca2+运输的新候选物，跨膜Bax抑制剂Motif containing protein 5 （TMBIM5）。我们提出TMBIM5是一个线粒体Ca2+通道，对线粒体功能很重要，基于已发表的和我们自己的初步数据，这些数据表明它是i)一个定位于线粒体内膜的多膜跨越蛋白，ii)属于细胞膜内进化保守的pH依赖性Ca2+泄漏通道家族，iii)具有在TMBIM6及其细菌同源物BsYetJ中鉴定的负责pH传感的二天冬氨酸pH传感器。iv)它的敲除对线粒体Ca2+处理和呼吸有深远的影响，最后v) TMBIM5敲除对线粒体呼吸的巨大影响可以通过野生型而不是突变型TMBIM5来挽救，TMBIM5缺乏位于半疏水性假定通道环域中的酸性pH传感器D326残基。我们与该领域的专家合作，生成了TMBIM5功能因其假定的孔隙突变而失效的定制小鼠系，并将使用这些小鼠1)定义TMBIM5在线粒体Ca2+动力学中的功能，2)研究TMBIM5在线粒体生理学中的作用，以及3)阐明TMBIM5功能缺失小鼠的体内表型。我们的研究将在生物物理、细胞生物学和生理学的尺度上进行，并将提供TMBIM5在线粒体生理学中的明确功能，并为疾病模型的转化研究开辟新的途径。

Many roles of mitochondria are related to their ability to take up Ca2+. The major driving force of this mitochondrial Ca2+ uptake is the negative membrane potential across the inner mitochondrial membrane. The major channel mediating the inward Ca2+ current is the mitochondrial Ca2+ uniporter (MCU), a protein located at the inner mitochondrial membrane. Despite this presumed importance, knockout of MCU in mice showed only minor physiological defects, suggesting yet unknown backup systems. This project focuses on a novel candidate for mitochondrial Ca2+ transport, Transmembrane Bax Inhibitor Motif containing protein 5 (TMBIM5). We propose that TMBIM5 is a mitochondrial Ca2+ channel important for mitochondrial function based on published and own preliminary data that demonstrate that it is i) a multi-membrane spanning protein localized to the inner mitochondrial membrane, ii) belongs to a family of evolutionarily conserved pH-dependent Ca2+ leak channels in intracellular membranes, iii) possesses the di-aspartyl pH sensor responsible for pH sensing identified in TMBIM6 and its bacterial homologue BsYetJ, iv) its knockout has profound effects on mitochondrial Ca2+ handling and respiration, and finally v) the fact that the dramatic effects of TMBIM5 knockout on mitochondrial respiration can be rescued by wildtype but not mutant TMBIM5 lacking the acidic pH sensor D326 residue located in the semi-hydrophobic putative channel loop domain. We have teamed up with experts in the field and generated bespoke mouse lines with TMBIM5 function nullified by mutations in its putative pore and will use these mice to 1) define the function of TMBIM5 in mitochondrial Ca2+ dynamics, to 2) investigate the role of TMBIM5 in mitochondrial physiology, and 3) to elucidate the in vivo phenotype of TMBIM5 loss-of-function mice. Our studies will be conducted at biophysical, cell biological and physiological scales and will provide a definitive account of TMBIM5 function in mitochondrial physiology and open up novel avenues for translational research in disease models.