title: Cysteine residues required for the attachment of the light chain in human IgA2.
abstract: In humans, there are two subclasses of IgA, IgA1 and IgA2, with IgA2 existing as three allotypes, IgA2m(1), IgA2m(2) and IgA2(n). In IgA1, Cys(133) in C(H)1 forms the disulfide bond to the L chain. Our previous studies indicated that in IgA2 lacking Cys(133), a disulfide bond forms between the alpha-chain and the L chain when Cys(220) is followed by Arg(221), but not when Cys(220) is followed by Pro(221), suggesting that the Cys in C(H)1 might be involved in disulfide bonding to the L chain. However, here we show that covalent assembly of the H and L chains in IgA2(n) requires hinge-proximal Cys(241) and Cys(242) in C(H)2 and not Cys(196) or Cys(220) in C(H)1. Using pulse-chase experiments, we have demonstrated that wild-type IgA2(n) with Arg(221) and Cys(241) and Cys(242) assembles through a disulfide-bonded HL intermediate. In contrast, the major intermediate for IgA2 m(1) with Pro(221) assembly was H(2) even though both Cys(241) and Cys(242) were present. Only a small fraction of IgA2 m(1) assembles through disulfide-bonded HL. Overall, our studies indicate that for IgA2 covalent assembly of the H and L chains requires the hinge-proximal cysteines in C(H)2 and that the structure of C(H)1 influences the efficiency with which this covalent bond forms.
authors.affiliation: Department of Microbiology, Immunology and Molecular Genetics and Molecular Biology Institute, University of California, Los Angeles 90095, USA. kotec@lifesci.ucla.edu
authors.forename: Koteswara R
authors.initials: KR
authors.lastname: Chintalacharuvu
authors.forename: Li J
authors.initials: LJ
authors.lastname: Yu
authors.forename: Nishant
authors.initials: N
authors.lastname: Bhola
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Christine Z
authors.initials: CZ
authors.lastname: Fernandez
authors.forename: Sherie L
authors.initials: SL
authors.lastname: Morrison
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003545:Cysteine / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004220:Disulfides / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007070:Immunoglobulin A / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D007126:Immunoglobulin Allotypes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007132:Immunoglobulin Isotypes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007147:Immunoglobulin Light Chains / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017510:Protein Folding; D011499:Protein Processing, Post-Translational / Q000235:genetics; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D004220:Disulfides; D007070:Immunoglobulin A; D007126:Immunoglobulin Allotypes; D007132:Immunoglobulin Isotypes; D007147:Immunoglobulin Light Chains; D003545:Cysteine