Glycosylation of proteins can modulate their function in a striking variety of systems, including immune responses, neuronal activities and development. The Drosophila protein, Chaoptin ( Chp), is essential for the development and maintenance of photoreceptor cells. This protein is heavily glycosylated, but the possible role of this glycosylation is not well- understood. Here we show that mutations introduced into about 1/ 3 of 16 potential N- linked glycosylation sites within Chp impaired its cell adhesive activities when expressed in Drosophila S2 cells. Mutation of 2/ 3 of the glycosylation sites resulted in a marked decrease in Chp protein abundance. These results suggest that Nlinked glycosylation of Chp is essential for its stability and activity. (c) 2008 Federation of European Biochemical Societies. Published by Elsevier B. V. All rights reserved.