PDZ domain-containing protein 8
mitochondrial calcium ion homeostasis
ER-mitochondria tethering by PDZD8 regulates Ca<sup>2+</sup> dynamics in mammalian neurons.
Interfaces between organelles are emerging as critical platforms for many biological responses in eukaryotic cells. In yeast, the ERMES complex is an endoplasmic reticulum (ER)-mitochondria tether composed of four proteins, three of which contain a SMP (synaptotagmin-like mitochondrial-lipid binding protein) domain. No functional ortholog for any ERMES protein has been identified in metazoans. Here, we identified PDZD8 as an ER protein present at ER-mitochondria contacts. The SMP domain of PDZD8 is functionally orthologous to the SMP domain found in yeast Mmm1. PDZD8 was necessary for the formation of ER-mitochondria contacts in mammalian cells. In neurons, PDZD8 was required for calcium ion (Ca<sup>2+</sup>) uptake by mitochondria after synaptically induced Ca<sup>2+</sup>-release from ER and thereby regulated cytoplasmic Ca<sup>2+</sup> dynamics. Thus, PDZD8 represents a critical ER-mitochondria tethering protein in metazoans. We suggest that ER-mitochondria coupling is involved in the regulation of dendritic Ca<sup>2+</sup> dynamics in mammalian neurons.