Interplay of J chain and disulfide bonding in assembly of polymeric IgM.
Normal mouse IgM is synthesized as hexamers in the absence of J chain and as pentamers in its presence. Previous work has suggested that polymer size is also closely related to formation of the inter-mu chain disulfide bond mediated by cysteine 414, one of three cysteines involved in inter-mu chain bonding. This correlation in turn suggested that formation of C414-C414 might be required for J chain to influence how IgM assembles and that formation of C414-C414 might affect the J chain/IgM stoichiometry. To test such hypotheses we have used cell lines which either expressed or did not express J chain to produce IgM in which serine was substituted for C414. In contrast to the case of IgM assembled from normal mu chains, IgM-S414 was secreted mostly as pentamers and tetramers but not as hexamers, irrespective of J chain synthesis. These results indicate that the role of J chain as modulator of IgM structure and function requires C414. Moreover, a more detailed analysis of the structure of J-plus and J-minus IgM-S414 revealed that J chain, in fact, influenced the nature of secreted IgM-S414: In the absence of J chain, some IgM-S414 was secreted as dimers and trimers, while in the presence of J chain, some IgM was secreted as non-covalently assembled pentamers. These results imply that disulfide bonding can occur differently from the pattern depicted in conventional models of IgM structure.
Fazel
S
S
Department of Immunology, University of Toronto, Ontario, Canada.
Wiersma
E J
EJ
Shulman
M J
MJ
D000818:Animals; D001704:Biopolymers / Q000737:chemistry* / Q000378:metabolism; D004220:Disulfides / Q000737:chemistry* / Q000378:metabolism; D006461:Hemolysis; D006825:Hybridomas / Q000378:metabolism; D007144:Immunoglobulin J-Chains / Q000737:chemistry* / Q000378:metabolism; D007075:Immunoglobulin M / Q000737:chemistry*; D051379:Mice; D008956:Models, Chemical; D008961:Models, Structural; D012333:RNA, Messenger / Q000378:metabolism; D014461:Ultracentrifugation
D001704:Biopolymers; D004220:Disulfides; D007144:Immunoglobulin J-Chains; D007075:Immunoglobulin M; D012333:RNA, Messenger