Identification of MOSPD2, a novel molecular velcro bridging cellular organelles with the endoplasmic reticulum
MOSPD2 (green) is a resident protein of the endoplasmic reticulum (top cell). MOSPD2 allows the formation of contact sites between the endoplasmic reticulum and a wide variety of cellular organelles. Here, MOSPD2 allows the formation of contact sites between the endoplasmic reticulum and mitochondria (magenta, middle cell) as well as between the reticulum and endosomes (magenta, lower cell). Contact sites appear in white (middle and bottom).
June 1, 2018
Membrane contact sites are newly identified cellular structures that facilitate the communication and molecular exchanges between the different organelles of the cell. A study carried out by Catherine Tomasetto's team characterized a new protein called MOtile SPerm Domain-containing protein 2 (MOSPD2), which mediates the formation of contact sites between the endoplasmic reticulum and other cellular organeles such as endosomes, mitochondria and the Golgi apparatus. These results are published on June 1st 2018 in EMBO reports.
Eukaryotic cells are divided into functionally specialized sub-regions named organelles, which remain separated entities thanks to a limiting membrane. Within a cell, communications between organelles are coordinated by newly identified specific subcellular structures, called membrane contact sites. At these sites, the membranes of two distinct organelles are in close apposition.
The endoplasmic reticulum seems to be at the center of this type of communication. Indeed, this network of tubes and sheets which extends throughout the entire cytoplasm establishes extensive contacts with most organelles. On the surface of this network, VAP proteins are anchor points for proteins present on the surface of other organelles. VAP proteins interact with small protein motifs, called FFAT, present on different proteins located on other organelles such as endosomes, mitochondria and Golgi, thus bringing together the membranes of the ER and these other organelles.
Surprisingly, most contacts between the endoplasmic reticulum and the other organelles persist in the absence of VAP proteins, suggesting the presence of compensatory mechanisms. Accordingly, researchers proposed that there could be one or more other endoplasmic reticulum proteins involved in membrane contact site formation.
In this study, using a proteomic approach, the researchers identified a new protein from the surface of the endoplasmic reticulum called MOtile SPerm Domain-containing protein 2 (MOSPD2). They showed that MOSPD2 has a protein domain that binds the FFAT motif. By interacting with proteins having this motif, MOSPD2 build membrane contact sites between a variety of cellular organelles and the endoplasmic reticulum.
Thus, researchers have identified a new anchor point that links the endoplasmic reticulum with a variety of distinct organelles and coordinates the interaction between organelles.
This study was funded by the League Against Cancer, Institut national du cancer and Ministère de l’Enseignement supérieur et de la Recherche