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Functional and structural characterisation of human colostrum free secretory component

Almogren, A; Bonner, A; Perkins, SJ; Kerr, MA; (2009) Functional and structural characterisation of human colostrum free secretory component. MOL IMMUNOL , 46 (7) 1534 - 1541. 10.1016/j.molimm.2008.12.022.

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Abstract

Secretory component (SC) in association with polymeric IgA (pIgA) forms secretory IgA (SIgA), the major antibody active at mucosal surfaces. SC also exists in a free form in secretions, with innate neutralizing properties against important pathogens. IgA-bound SC and free secretory component (FSC) are both produced by proteolytic cleavage of the polymeric Ig receptor whose function is to transport IgA and IgM across mucosal epithelia. Although the proteases have not been characterised and the site(s) of cleavage of the polymeric Ig receptor has been debated, it has been assumed that bound and free SC are produced by cleavage at the same site. Here we show by SIDS-PAGE analyses that FSC is slightly smaller than SIgA1- or SIgA2-bound SC when purified simultaneously. The FSC preparation was functionally active, shown by binding to dimeric and polymeric IgA, and by its ability to trigger a respiratory burst by binding to 'SC receptors' on eosinophils. We also show that FSC from different human secretions have different molecular sizes. The solution structure of FSC from colostrum was studied by analytical ultracentrifugation and X-ray scattering. The sedimentation coefficient of 4.25 S is close to that for recombinant FSC. The X-ray scattering curve showed that FSC adopts a compact structure in solution which corresponds well to the J-shaped domain arrangement determined previously for recombinant FSC which terminates at residue Arg585. The smaller sizes of the FSC forms are attributable to variable cleavages of the C-terminal linker region, and may result from the absence of dimeric IgA. The FSC modelling accounts for the lack of effect of the C-terminal linker on the known functions of FSC. (C) 2009 Elsevier Ltd. All rights reserved.

Type: Article
Title: Functional and structural characterisation of human colostrum free secretory component
DOI: 10.1016/j.molimm.2008.12.022
Keywords: Analytical ultracentrifugation, Immunoglobulin A, Mucosal immunity, X-ray scattering, POLYMERIC IMMUNOGLOBULIN RECEPTOR, ENTEROTOXIGENIC ESCHERICHIA-COLI, HUMAN-MILK, X-RAY, PROTEASE INHIBITORS, NEUTRON-SCATTERING, HUMAN EOSINOPHILS, MUCOSAL SURFACES, DIMERIC IGA1, BINDING
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences > Structural and Molecular Biology
URI: http://discovery.ucl.ac.uk/id/eprint/150247
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