Cysteine residues required for the attachment of the light chain in human IgA2.
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.
Chintalacharuvu
Koteswara R
KR
Department of Microbiology, Immunology and Molecular Genetics and Molecular Biology Institute, University of California, Los Angeles 90095, USA. kotec@lifesci.ucla.edu
Yu
Li J
LJ
Bhola
Nishant
N
Kobayashi
Kunihiko
K
Fernandez
Christine Z
CZ
Morrison
Sherie L
SL
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
D004220:Disulfides; D007070:Immunoglobulin A; D007126:Immunoglobulin Allotypes; D007132:Immunoglobulin Isotypes; D007147:Immunoglobulin Light Chains; D003545:Cysteine