title: Cysteines in CH1 underlie retention of unassembled Ig heavy chains.
abstract: Conformation, structure, and oligomeric state of immunoglobulins not only control quality and functional properties of antibodies but are also critical for immunoglobulins secretion. Unassembled immunoglobulin heavy chains are retained intracellularly by delayed folding of the C(H)1 domain and irreversible interaction of BiP with this domain. Here we show that the three C(H)1 cysteines play a central role in immunoglobulin folding, assembly, and secretion. Remarkably, ablating all three C(H)1 cysteines negates retention and enables BiP cycling and non-canonical folding and assembly. This phenomenon is explained by interdependent formation of intradomain and interchain disulfides, although both bonds are dispensable for secretion. Substituting Cys-195 prevents formation not only of the intradomain disulfide, but also of the interchain disulfide bond with light chain, BiP displacement, and secretion. Mutating the light chain-interacting Cys-128 hinders disulfide bonding of intradomain cysteines, allowing their opportunistic bonding with light chain, without hampering secretion. We propose that the role of C(H)1 cysteines in immunoglobulin assembly and secretion is not simply to engage in disulfide bridges, but to direct proper folding and interact with the retention machinery.
authors.affiliation: Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel.
authors.forename: Yechiel
authors.initials: Y
authors.lastname: Elkabetz
authors.forename: Yair
authors.initials: Y
authors.lastname: Argon
authors.forename: Shoshana
authors.initials: S
authors.lastname: Bar-Nun
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D003545:Cysteine / Q000737:chemistry*; D017931:DNA Primers / Q000737:chemistry; D004220:Disulfides / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D000091342:Endoplasmic Reticulum Chaperone BiP; D006026:Glycoside Hydrolases / Q000737:chemistry; D006360:Heat-Shock Proteins / Q000737:chemistry*; D007143:Immunoglobulin Heavy Chains / Q000737:chemistry*; D007147:Immunoglobulin Light Chains / Q000737:chemistry; D047468:Immunoprecipitation; D051379:Mice; D008954:Models, Biological; D018832:Molecular Chaperones / Q000737:chemistry*; D008969:Molecular Sequence Data; D009154:Mutation; D010100:Oxygen / Q000737:chemistry; D010196:Pancreatic Elastase / Q000737:chemistry; D010206:Papain / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry; D014162:Transfection
chemical_list: D017931:DNA Primers; D004220:Disulfides; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D007143:Immunoglobulin Heavy Chains; D007147:Immunoglobulin Light Chains; D018832:Molecular Chaperones; D011506:Proteins; D006026:Glycoside Hydrolases; D010196:Pancreatic Elastase; D010206:Papain; D003545:Cysteine; D010100:Oxygen