J chain in the nurse shark: implications for function in a lower vertebrate.
J chain is a small polypeptide covalently attached to polymeric IgA and IgM. In humans and mice, it plays a role in binding Ig to the polymeric Ig receptor for transport into secretions. The putative orthologue of mammalian J chain has been identified in the nurse shark by sequence analysis of cDNA and the polypeptide isolated from IgM. Conservation with J chains from other species is relatively poor, especially in the carboxyl-terminal portion, and, unlike other J chains, the shark protein is not acidic. The only highly conserved segment in all known J chains is a block of residues surrounding an N-linked glycosylation site. Of the eight half-cystine residues that are conserved in mammalian J chains, three are lacking in the nurse shark, including two in the carboxyl-terminal segment that have been reported to be required for binding of human J chain-containing IgA to secretory component. Taken together with these data, the relative abundance of J chain transcripts in the spleen and their absence in the spiral valve (intestine) suggest that J chain in nurse sharks may not have a role in Ig secretion. Analysis of J chain sequences in diverse species is in agreement with accepted phylogenetic relationships, with the exception of the earthworm, suggesting that the reported presence of J chain in invertebrates should be reassessed.
Hohman
Valerie S
VS
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Stewart
Sue E
SE
Rumfelt
Lynn L
LL
Greenberg
Andrew S
AS
Avila
David W
DW
Flajnik
Martin F
MF
Steiner
Lisa A
LA
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015139:Blotting, Southern; D018076:DNA, Complementary / Q000302:isolation & purification; D005786:Gene Expression Regulation / Q000276:immunology; D015723:Gene Library; D006801:Humans; D007133:Immunoglobulin Joining Region / Q000096:biosynthesis / Q000235:genetics / Q000302:isolation & purification* / Q000502:physiology*; D008969:Molecular Sequence Data; D009835:Oligochaeta / Q000276:immunology; D009928:Organ Specificity / Q000235:genetics / Q000276:immunology; D010446:Peptide Fragments / Q000235:genetics / Q000302:isolation & purification; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017423:Sequence Analysis, RNA; D012754:Sharks / Q000276:immunology*; D013154:Spleen / Q000276:immunology / Q000378:metabolism
D018076:DNA, Complementary; D007133:Immunoglobulin Joining Region; D010446:Peptide Fragments