title: Biological inferences from IgM binding characteristics of recombinant human secretory component mutants.
abstract: The polymeric immunoglobulin receptor (pIgR) or membrane secretory component (SC) selectively transports polymeric IgA and IgM across secretory epithelial cells to mucosal surfaces. The ligand binding ectodomain consists of five homologous Ig-like domains with domain I being an absolute requirement for binding. The role of DII to V in IgM binding remains unknown. Here, using in vitro refolded non-glycosylated recombinant domain deletion mutants of human SC, we show by biological and biophysical binding assays that DII to V are required for high affinity binding to IgM. Competitive binding analysis, by whole cell ELISA, showed that DII-V significantly increase the affinity of recombinant SC for IgM (K(i)=2.42 nM) as opposed to recombinant DI only (K(i)=44.8 nM). Lastly, we provide qualitative data highlighting the complexity of measuring the IgM/SC interaction using surface plasmon resonance spectroscopy.
authors.affiliation: Department of Biochemistry and Microbiology, Faculty of Science, Nelson Mandela Metropolitan University South Campus, Summerstrand, Port Elizabeth, South Africa. e.prinsloo@ru.ac.za
authors.forename: Earl
authors.initials: E
authors.lastname: Prinsloo
authors.forename: Vaughan
authors.initials: V
authors.lastname: Oosthuizen
authors.forename: Maryna
authors.initials: M
authors.lastname: Van de Venter
authors.forename: Ryno J
authors.initials: RJ
authors.lastname: Naudé
mesh_terms: D001693:Biological Transport, Active; D004797:Enzyme-Linked Immunosorbent Assay; D015870:Gene Expression; D005818:Genetic Engineering; D006801:Humans; D007075:Immunoglobulin M / Q000276:immunology / Q000378:metabolism*; D011485:Protein Binding / Q000235:genetics / Q000276:immunology*; D017510:Protein Folding; D054730:Protein Interaction Domains and Motifs / Q000235:genetics* / Q000276:immunology; D019056:Receptors, Polymeric Immunoglobulin / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D017384:Sequence Deletion
chemical_list: D007075:Immunoglobulin M; D019056:Receptors, Polymeric Immunoglobulin; D011994:Recombinant Proteins; C024242:polymeric IgM