Wild type and constitutively activated forms of the Drosophila Toll receptor have different patterns of N-linked glycosylation.

Toll is a Drosophila membrane protein related in sequence to the mammalian platelet glycoprotein 1B and to the interleukin-1 receptor. It mediates a signal transduction pathway leading to the development of dorsoventral polarity in the Drosophila embryo. In this paper we show that a constitutively activated mutant receptor, Toll10B, is processed into a distinct isoform of slower electrophoretic mobility when compared with the wild type molecule in both cell lines and the embryo. The wild type protein can also be processed into this form if over-expressed but in the embryo is present as the smaller species. We show that the decrease in the mobility of Toll10B and over-expressed wild type receptors is caused by altered patterns of N-linked glycosylation and that both forms are secreted to the cell surface. On the basis of these results, we propose that the Toll10B receptor is unable to associate with a limiting co-factor which when bound directly or indirectly masks supplementary N-linked glycosylation sites.