Analysis of IgM structures involved in J chain incorporation.
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.
Wiersma
E J
EJ
Department of Immunology, University of Toronto, Ontario, Canada.
Chen
F
F
Bazin
R
R
Collins
C
C
Painter
R H
RH
Lemieux
R
R
Shulman
M J
MJ
D000595:Amino Acid Sequence; D000818:Animals; D001216:Asparagine / Q000378:metabolism; D002460:Cell Line; D006031:Glycosylation; D007127:Immunoglobulin Constant Regions / Q000235:genetics; D007144:Immunoglobulin J-Chains / Q000378:metabolism*; D007075:Immunoglobulin M / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D007148:Immunoglobulin mu-Chains / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D017384:Sequence Deletion / Q000276:immunology; D013329:Structure-Activity Relationship
D007127:Immunoglobulin Constant Regions; D007144:Immunoglobulin J-Chains; D007075:Immunoglobulin M; D007148:Immunoglobulin mu-Chains; D001216:Asparagine