title: Structural and functional analysis of J chain-deficient IgM.
abstract: Previous studies have discerned two forms of polymeric mouse IgM: moderately cytolytic (complement-activating) pentamer, which contains J chain, and highly cytolytic hexamer, which lacks J chain. To investigate the relationships among polymeric structure, J chain content, and cytolytic activity, we produced IgM in J chain-deficient and J chain-proficient mouse hybridoma cell lines. Both hexamer and pentamer were produced in the absence as well as the presence of J chain. Hexameric IgM activated (guinea pig) complement approximately 100-fold more efficiently than did J chain-deficient pentamer, which, in turn, was more active than J chain-containing pentamer. These results are consistent with the hypothesis that J chain-containing pentamer cannot activate complement. We also analyzed the structure of IgM-S337, in which the mu-chain bears the C337S substitution. Like normal IgM, IgM-S337 was formed as a hexamer and as both J chain deficient- and J chain-containing pentamers. Unlike normal IgM, IgM-S337 dissociated in SDS into various subunits. For IgM-S337 pentamer, the predominant subunits migrated as mu2kappa2 and mu4kappa4, and the subunit distribution was unaltered by J chain. However, J chain was found only in the mu2kappa2 species, suggesting that some arrangement of inter-mu bonds directs incorporation of J chain. IgM-S337 hexamer also dissociated to mu2kappa2 and mu4kappa4, but also yielded several species migrating much more slowly in SDS-PAGE than wild-type mu12kappa12. To account for these forms, we propose that each mu-chain can interact with three other mu-chains and that some hexameric molecules contain two catenated mu6kappa6 circles.
authors.affiliation: Department of Immunology, University of Toronto, Ontario, Canada.
authors.forename: E J
authors.initials: EJ
authors.lastname: Wiersma
authors.forename: C
authors.initials: C
authors.lastname: Collins
authors.forename: S
authors.initials: S
authors.lastname: Fazel
authors.forename: M J
authors.initials: MJ
authors.lastname: Shulman
mesh_terms: D000818:Animals; D002460:Cell Line; D004220:Disulfides / Q000737:chemistry; D007144:Immunoglobulin J-Chains / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D007075:Immunoglobulin M / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D051379:Mice; D008958:Models, Molecular; D013329:Structure-Activity Relationship; D014162:Transfection
chemical_list: D004220:Disulfides; D007144:Immunoglobulin J-Chains; D007075:Immunoglobulin M