Binding of secretory component to protein 511, a pIgA mouse protein lacking 36 amino acid residues of the Cα3 domain

Protein 511, a murine IgA protein described previously by Robinson and Appella [Proc. natn. Acad. Sci. U.S.A. 77, 4909-4913 (1980)] which lacks 36 amino acids in the C alpha 3 domain, was tested for its ability to bind to radiolabelled secretory component (125I-rat SC) and to be transported from blood to bile in the rat, a function described previously to be mediated by the poly Ig receptor (pIg R). When compared to other mouse pIgA proteins, the naturally occurring mutant protein 511 bound 125I-rat SC and was transported from blood to bile in a manner indistinguishable from wild-type pIgA protein. We conclude that the region of Fc alpha which is missing in protein 511, is not involved in mediating the binding of pIgA to the pIg R.