Editing Mitochondrion (section)

====Molecular basis for tethering====
Recent advances in the identification of the [[tether (cell biology)|tethers]] between the mitochondrial and ER membranes suggest that the scaffolding function of the molecular elements involved is secondary to other, non-structural functions. In yeast, ERMES, a multiprotein complex of interacting ER- and mitochondrial-resident membrane proteins, is required for lipid transfer at the MAM and exemplifies this principle. One of its components, for example, is also a constituent of the protein complex required for insertion of transmembrane beta-barrel proteins into the lipid bilayer.<ref name="Osman-2011"/> However, a [[Homology (biology)|homologue]] of the ERMES complex has not yet been identified in mammalian cells. Other proteins implicated in scaffolding likewise have functions independent of structural tethering at the MAM; for example, ER-resident and mitochondrial-resident mitofusins form heterocomplexes that regulate the number of inter-organelle contact sites, although mitofusins were first identified for their role in [[Mitochondrial fission|fission]] and [[Mitochondrial fusion|fusion]] events between individual mitochondria.<ref name="Rizzuto-2009"/> [[Glucose]]-related protein 75 (grp75) is another dual-function protein. In addition to the matrix pool of grp75, a portion serves as a chaperone that physically links the mitochondrial and ER Ca{{sup|2+}} channels VDAC and IP3R for efficient Ca{{sup|2+}} transmission at the MAM.<ref name="Rizzuto-2009"/><ref name="Hayashi-2009"/> Another potential tether is [[Sigma-1 receptor|Sigma-1R]], a non-opioid receptor whose stabilization of ER-resident IP3R may preserve communication at the MAM during the metabolic stress response.<ref>{{cite journal | vauthors = Marriott KS, Prasad M, Thapliyal V, Bose HS | title = σ-1 receptor at the mitochondrial-associated endoplasmic reticulum membrane is responsible for mitochondrial metabolic regulation | journal = The Journal of Pharmacology and Experimental Therapeutics | volume = 343 | issue = 3 | pages = 578–586 | date = December 2012 | pmid = 22923735 | pmc = 3500540 | doi = 10.1124/jpet.112.198168 }}</ref><ref>{{cite journal | vauthors = Hayashi T, Su TP | title = Sigma-1 receptor chaperones at the ER-mitochondrion interface regulate Ca(2+) signaling and cell survival | journal = Cell | volume = 131 | issue = 3 | pages = 596–610 | date = November 2007 | pmid = 17981125 | doi = 10.1016/j.cell.2007.08.036 | doi-access = free }}</ref>

[[File:ERMES.png|thumb|alt=ERMES tethering complex.|Model of the yeast multimeric tethering complex, ERMES]]