Interplay of J chain and disulfide bonding in assembly of polymeric IgM

Int Immunol. 1997 Aug;9(8):1149-58. doi: 10.1093/intimm/9.8.1149.

Abstract

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.

MeSH terms

  • Animals
  • Biopolymers / chemistry*
  • Biopolymers / metabolism
  • Disulfides / chemistry*
  • Disulfides / metabolism
  • Hemolysis
  • Hybridomas / metabolism
  • Immunoglobulin J-Chains / chemistry*
  • Immunoglobulin J-Chains / metabolism
  • Immunoglobulin M / chemistry*
  • Mice
  • Models, Chemical*
  • Models, Structural
  • RNA, Messenger / metabolism
  • Ultracentrifugation

Substances

  • Biopolymers
  • Disulfides
  • Immunoglobulin J-Chains
  • Immunoglobulin M
  • RNA, Messenger