Unassembled Ig heavy chains do not cycle from BiP in vivo but require light chains to trigger their release.
Unassembled Ig heavy chains are retained in the ER via the binding of BiP to the C(H)1 domain, which remains unoxidized. Interestingly, this domain folds rapidly, albeit nonproductively, when heavy chains are released from BiP in vitro with ATP. The in vivo cycling of BiP from heavy chains was monitored using BiP ATPase mutants as kinetic traps. Our data suggest that BiP does not cycle from the C(H)1 domain of free heavy chains. However, heavy and light chain assembly occurs rapidly and requires the ATP-dependent release of BiP. We propose that BiP's ATPase cycle is stalled or nonproductive when it is bound to free heavy chains. The binding of light chains to the complex reactivates the cycle and releases BiP.
Vanhove
M
M
Department of Tumor Cell Biology, St. Jude Children's Research Hospital, 332 North Lauderdale, Memphis, TN 38105, USA.
Usherwood
Y K
YK
Hendershot
L M
LM
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D007127:Immunoglobulin Constant Regions / Q000378:metabolism; D007143:Immunoglobulin Heavy Chains / Q000378:metabolism*; D007147:Immunoglobulin Light Chains / Q000502:physiology*; D018832:Molecular Chaperones / Q000378:metabolism*; D017510:Protein Folding
D002352:Carrier Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D007127:Immunoglobulin Constant Regions; D007143:Immunoglobulin Heavy Chains; D007147:Immunoglobulin Light Chains; D018832:Molecular Chaperones; D000255:Adenosine Triphosphate