The ERMES complex and ER–mitochondria connections

Abstract

Cellular organelles need to communicate in order to co-ordinate homoeostasis of the compartmentalized eukaryotic cell. Such communication involves the formation of membrane contact sites between adjacent organelles, allowing privileged exchange of metabolites and information. Using a synthetic protein designed to artificially tether the ER (endoplasmic reticulum) to mitochondria, we have discovered a yeast protein complex naturally involved in establishing and maintaining contact sites between these two organelles. This protein complex is physiologically involved in a plethora of mitochondrial processes, suggesting that ER–mitochondria connections play a central co-ordinating role in the regulation of mitochondrial biology. Recent biochemical characterization of this protein complex led to the discovery that GTPases of the Miro family are part of ER–mitochondria connections. The yeast Miro GTPase Gem1 localizes to ER–mitochondria interface and influences the size and distribution of mitochondria. Thus Miro GTPases may serve as regulators of the ER–mitochondria connection.