Analysis of IgM structures involved in J chain incorporation

• Published in: The Journal of immunology (1950) Vol. 158; no. 4; pp. 1719 - 1726
• Main Authors: Wiersma, EJ, Chen, F, Bazin, R, Collins, C, Painter, RH, Lemieux, R, Shulman, MJ
• Format: Journal Article
• Language: English
• Published: United States Am Assoc Immnol 15-02-1997
• Subjects: Amino Acid Sequence; Animals; Asparagine - metabolism; Cell Line; Glycosylation; Immunoglobulin Constant Regions - genetics; Immunoglobulin J-Chains - metabolism; Immunoglobulin M - chemistry; Immunoglobulin M - genetics; Immunoglobulin M - metabolism; Immunoglobulin mu-Chains - genetics; Mice; Molecular Sequence Data; Sequence Deletion - immunology; Structure-Activity Relationship
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.158.4.1719

J chain is associated with pentameric IgM and polymeric IgA. In IgM, J chain is disulfide bonded to the C575 residue of the mu-chain, located in the mu tail piece (mu tp). Previous studies indicated that mu tp is not sufficient to mediate J chain incorporation into polymeric Ig. In this study, we analyzed which other C mu domains are involved in J chain incorporation. Three altered forms of mouse IgM were analyzed: IgM lacking the C mu 1 domain, IgM in which the C mu 2 and C mu 3 domains were replaced by the hinge region and the C gamma 2 domain of IgG2b, and IgM, in which the C mu 4 domain was replaced by C gamma 3. We found that neither C mu 1, C mu 2, nor C mu 3 was absolutely required for J chain incorporation. The importance of C mu 4 could not be fully analyzed because the C gamma 3 replacement mutant failed to form polymers. Also, we found that the glycosylation site at asparagine 563 of mu tp was important for J chain incorporation. Disruption of this site by replacement of either asparagine 563 by tyrosine or serine 565 by phenylalanine resulted in diminished J chain incorporation and increased production of hexameric IgM. These results demonstrate the importance of structural elements located close to mu tp in the incorporation of J chain into IgM.