International Immunology Advance Access originally published online on July 28, 2006
International Immunology 2006 18(9):1385-1396; doi:10.1093/intimm/dxl072
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Identification of disulfide bonds in the Ig-
/Ig-ß component of the B cell antigen receptor using the Drosophila S2 cell reconstitution system
Max Planck-Institut für Immunbiologie and University of Freiburg, Biologie III Stübeweg 51, 79108 Freiburg, Germany
Correspondence to: W. W. A. Schamel; E-mail: schamel{at}immunbio.mpg.de
Structural information about immune receptor complexes is important for understanding signal transduction mechanisms. We have used the Drosophila S2 cell reconstitution system for identification of disulfide bonds within and between CD79a (Ig-
) and CD79b (Ig-ß), the heterodimeric signal transducing element of the B cell antigen receptor (BCR). Cysteines 113 and 135 of Ig-
and Ig-ß, respectively, form the intermolecular disulfide bridge stabilizing the Ig-
/Ig-ß heterodimer in both S2 cells and the B cell line J558L. Furthermore, using transfected S2 cells, two putative intramolecular disulfide bonds in the Ig-like domain of Ig-ß were identified. Ig-ßC65 and Ig-ßC120 form the canonical Ig fold disulfide bond. In addition, Ig-ßC43 and Ig-ßC124 also bind covalently. Individual cysteine to serine mutations in Ig-
had no influence on membrane-bound Ig (mIg)-M expression on the surface of S2 cells. In contrast, mIgM expression on the surface of B cells expressing Ig-
C113S was reduced, indicating that this intermolecular bond is prerequisite for efficient IgM-BCR formation. Our data also suggest that the Ig-
/Ig-ß heterodimer can assemble into oligomers.
Keywords: BCR assembly, cysteine mutants, Ig-
/Ig-ß heterodimer, Ig fold, surface mIgM expression
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