The ER lumen contains:
Endoplasmic reticulum lumen is specialized folding compartment with oxidizing redox potential, high calcium millimolar and abundant chaperones distinguishing it from reducing cytosol. Newly translocated polypeptides entering via Sec61 encounter BiP also called GRP78, luminal Hsp70 family member binding transiently to exposed hydrophobic segments in ATP-regulated cycle where ATP binding opens substrate binding domain, hydrolysis closes it trapping unfolded chain preventing aggregation and promoting correct disassembly of aggregates. Cooperation with co-chaperone ERdj proteins stimulates ATPase,
Ref: Kozlov Trends Biochem; ER lumen BiP GRP78 Hsp70 folding quality control UPR sensor.
