Keratin 5 as an IgG Fc Binding Protein in Human Corneal Epithelium

Abstract

Abstract: : Purpose. We have focused on a phenomenon that rabbit and human immunoglobulin G (IgG) have a binding behavior toward human corneal epithelium and the previously suggested existence of an IgG Fc binding material which differed from Fc gamma receptors in this tissue. This study was carried out to investigate what the binding material was. Methods. Human corneal epithelium was homogenized in a buffer containing Triton X-100. The water-insoluble residue containing keratins was subjected to two-dimensional gel electrophoresis. Western blotting experiments were performed on the gel to detect binding materials with rabbit IgG Fc fragments and to locate keratin 3 and 12 which are major keratins in corneal epithelium. Spots in the gel binding with the Fc fragments were picked up and then subjected to peptide mass fingerprinting (PMF) analysis. Results. Following western blotting with the rabbit Fc fragments some spots (M.W. @ 60 kDa) were found to bind with the fragments. The binding materials were basic (pI 7.5-9.0) and identical to neither keratin 3 nor keratin 12. Results of PMF analysis showed all of the binding materials as keratin 5. Conclusions. These data suggest that rabbit IgG binds with keratin 5 in human corneal epithelium via the Fc region of the molecule.

Keywords: cornea: epithelium • cornea: basic science • protein structure/function