Editing Endoplasmic reticulum (section)

===Bioenergetics regulation of ER ATP supply by a CaATiER mechanism===
[[File:CaATiER model 081219.jpg|thumb|Ca2+-antagonized transport into the endoplasmic reticulum (CaATiER) model]]
The endoplasmic reticulum does not harbor an ATP-regeneration machinery, and therefore requires ATP import from mitochondria. The imported ATP is vital for the ER to carry out its house keeping cellular functions, such as for protein folding and trafficking.<ref>{{cite journal |last1=Clairmont |first1=CA |last2=De Maio |first2=A |last3=Hirschberg |first3=CB |title=Translocation of ATP into the lumen of rough endoplasmic reticulum-derived vesicles and its binding to luminal proteins including BiP (GRP 78) and GRP 94. |journal=The Journal of Biological Chemistry |date=25 February 1992 |volume=267 |issue=6 |pages=3983–90 |doi=10.1016/S0021-9258(19)50622-6 |pmid=1740446 |doi-access=free }}</ref>

The ER ATP transporter, SLC35B1/AXER, was recently cloned and characterized,<ref>{{cite journal |last1=Klein |first1=Marie-Christine |last2=Zimmermann |first2=Katharina |last3=Schorr |first3=Stefan |last4=Landini |first4=Martina |last5=Klemens |first5=Patrick A. W. |last6=Altensell |first6=Jacqueline |last7=Jung |first7=Martin |last8=Krause |first8=Elmar |last9=Nguyen |first9=Duy |last10=Helms |first10=Volkhard |last11=Rettig |first11=Jens |last12=Fecher-Trost |first12=Claudia |last13=Cavalié |first13=Adolfo |last14=Hoth |first14=Markus |last15=Bogeski |first15=Ivan |last16=Neuhaus |first16=H. Ekkehard |last17=Zimmermann |first17=Richard |last18=Lang |first18=Sven |last19=Haferkamp |first19=Ilka |title=AXER is an ATP/ADP exchanger in the membrane of the endoplasmic reticulum |journal=Nature Communications |date=28 August 2018 |volume=9 |issue=1 |pages=3489 |doi=10.1038/s41467-018-06003-9 |pmid=30154480 |pmc=6113206 |bibcode=2018NatCo...9.3489K }}</ref> and the mitochondria supply ATP to the ER through a ''Ca<sup>2+</sup>-antagonized transport into the ER'' (''CaATiER'') mechanism.<ref>{{cite journal |last1=Yong |first1=Jing |last2=Bischof |first2=Helmut |last3=Burgstaller |first3=Sandra |last4=Siirin |first4=Marina |last5=Murphy |first5=Anne |last6=Malli |first6=Roland |last7=Kaufman |first7=Randal J |title=Mitochondria supply ATP to the ER through a mechanism antagonized by cytosolic Ca<sup>2+</sup> |journal=eLife |date=9 September 2019 |volume=8 |doi=10.7554/eLife.49682 |pmid=31498082 |pmc=6763289 |doi-access=free }}</ref> The ''CaATiER'' mechanism shows sensitivity to cytosolic Ca<sup>2+</sup> ranging from high nM to low μM range, with the Ca<sup>2+</sup>-sensing element yet to be identified and validated.<ref>{{Cite journal |last1=Yong |first1=Jing |last2=Bischof |first2=Helmut |last3=Burgstaller |first3=Sandra |last4=Siirin |first4=Marina |last5=Murphy |first5=Anne |last6=Malli |first6=Roland |last7=Kaufman |first7=Randal J |title=Mitochondria supply ATP to the ER through a mechanism antagonized by cytosolic Ca2+ |journal=eLife |date=2019 |volume=8 |pages=e49682 |doi=10.7554/eLife.49682 |doi-access=free |issn=2050-084X |pmc=6763289 |pmid=31498082}}</ref>