Microenvironments of photoreceptor and interphotoreceptor matrix glycoconjugates

Enzyme-linked lectin cytochemical and biochemical analyses have been used to identify microdomains of retinal outer segments and interphotoreceptor matrix glycoconjugates. We have devised a highly reproducible trypsin digestion procedure to identify protease-resistant wheat germ agglutinin (WGA) domains on the distal tips of some photoreceptor outer segments, and on shed outer segment membrane in Xenopus laevis retina. WGA binding sites in the frog interphotoreceptor matrix were completely susceptible to trypsin digestion. In contrast, the cytochemical procedures revealed a distinct protease resistant WGA-positive microdomain in the interphotoreceptor matrix of rat (and probably human) retina at the outer segment-pigment epithelium interface. Neuraminidase digestion of sections of rat retina previously digested with trypsin essentially completely removed WGA binding sites in this microdomain. These results indicated that the protease-resistant carbohydrates were sialoglycoconjugates. A potential role for this pool of sialoglycoconjugates would be to mediate adhesion of the outer segment-pigment epithelium interface. Analysis of solubilized retina digested with trypsin and separated by polyacrylamide gel electrophoresis revealed a set of protease resistant WGA binding glycoprotein of Mr 60 kDa on nitrocellulose transblots which we hypothesize may be a component of the protease resistant microdomain at the outer segment-pigment epithelium interface of rat retina.