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Cysteine Residues Required for the Attachment of the Light Chain in Human IgA2¹

Koteswara R. Chintalacharuvu^2,, Li J. Yu, Nishant Bhola, Kunihiko Kobayashi, Christine Z. Fernandez and Sherie L. Morrison

^* Department of Microbiology, Immunology and Molecular Genetics and Molecular Biology Institute, University of California, Los Angeles, CA 90095; and Department of Pediatrics, Hokkaido University School of Medicine, Sapporo, Japan

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, Cys¹³³ in C_H1 forms the disulfide bond to the L chain. Our previous studies indicated that in IgA2 lacking Cys¹³³, a disulfide bond forms between the -chain and the L chain when Cys²²⁰ is followed by Arg²²¹, but not when Cys²²⁰ is followed by Pro²²¹, suggesting that the Cys in C_H1 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 Cys²⁴¹ and Cys²⁴² in C_H2 and not Cys¹⁹⁶ or Cys²²⁰ in C_H1. Using pulse-chase experiments, we have demonstrated that wild-type IgA2(n) with Arg²²¹ and Cys²⁴¹ and Cys²⁴² assembles through a disulfide-bonded HL intermediate. In contrast, the major intermediate for IgA2 m(1) with Pro²²¹ assembly was H₂ even though both Cys²⁴¹ and Cys²⁴² 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_H2 and that the structure of C_H1 influences the efficiency with which this covalent bond forms.

This article has been cited by other articles:

				K. R. Chintalacharuvu, P. D. Chuang, A. Dragoman, C. Z. Fernandez, J. Qiu, A. G. Plaut, K. R. Trinh, F. A. Gala, and S. L. Morrison Cleavage of the Human Immunoglobulin A1 (IgA1) Hinge Region by IgA1 Proteases Requires Structures in the Fc region of IgA Infect. Immun., May 1, 2003; 71(5): 2563 - 2570. [Abstract] [Full Text] [PDF]