Benner_2023_J.Biol.Chem__105361

In recent years, elegant glycomic and glycoproteomic approaches have revealed an intricate glycosylation profile of mammalian brain with enormous spatial and temporal diversities. Nevertheless, at a cellular level, it is unclear how these post-translational modifications (PTMs) affect various proteins to influence crucial neuronal properties. Here, we have investigated the impact of N-linked glycosylation on Neuroligins (NLGNs), a class of cell-adhesion molecules (CAMs) that play instructive roles in synapse organization. We found that endogenous NLGN proteins are differentially glycosylated across several regions of murine brain in a sex-independent but isoform-dependent manner. In both rodent primary neurons derived from brain sections and human neurons differentiated from stem cells, all NLGN variants were highly enriched with multiple N-glycan subtypes, which cumulatively ensured their efficient trafficking to the cell-surface. Removal of these N-glycosylation residues only had a moderate effect on NLGNs' stability or expression levels, but particularly enhanced their retention at the endoplasmic reticulum (ER). As a result, glycosylation-deficient NLGNs exhibited considerable impairments in their dendritic distribution and postsynaptic accumulation, which virtually eliminated their ability to recruit presynaptic terminals and significantly reduced NLGN overexpression -induced assemblies of both Glutamatergic and GABAergic synapse structures. Therefore, our results highlight an essential mechanistic contribution of N-linked glycosylations in facilitating the appropriate secretory transport of a major synaptic CAM and promoting its cellular function in neurons.