title: N-glycosylation at the SynCAM (synaptic cell adhesion molecule) immunoglobulin interface modulates synaptic adhesion.
abstract: Select adhesion molecules connect pre- and postsynaptic membranes and organize developing synapses. The regulation of these trans-synaptic interactions is an important neurobiological question. We have previously shown that the synaptic cell adhesion molecules (SynCAMs) 1 and 2 engage in homo- and heterophilic interactions and bridge the synaptic cleft to induce presynaptic terminals. Here, we demonstrate that site-specific N-glycosylation impacts the structure and function of adhesive SynCAM interactions. Through crystallographic analysis of SynCAM 2, we identified within the adhesive interface of its Ig1 domain an N-glycan on residue Asn(60). Structural modeling of the corresponding SynCAM 1 Ig1 domain indicates that its glycosylation sites Asn(70)/Asn(104) flank the binding interface of this domain. Mass spectrometric and mutational studies confirm and characterize the modification of these three sites. These site-specific N-glycans affect SynCAM adhesion yet act in a differential manner. Although glycosylation of SynCAM 2 at Asn(60) reduces adhesion, N-glycans at Asn(70)/Asn(104) of SynCAM 1 increase its interactions. The modification of SynCAM 1 with sialic acids contributes to the glycan-dependent strengthening of its binding. Functionally, N-glycosylation promotes the trans-synaptic interactions of SynCAM 1 and is required for synapse induction. These results demonstrate that N-glycosylation of SynCAM proteins differentially affects their binding interface and implicate post-translational modification as a mechanism to regulate trans-synaptic adhesion.
authors.affiliation: Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: Adam I
authors.initials: AI
authors.lastname: Fogel
authors.forename: Yue
authors.initials: Y
authors.lastname: Li
authors.forename: Joanna
authors.initials: J
authors.lastname: Giza
authors.forename: Qing
authors.initials: Q
authors.lastname: Wang
authors.forename: Tukiet T
authors.initials: TT
authors.lastname: Lam
authors.forename: Yorgo
authors.initials: Y
authors.lastname: Modis
authors.forename: Thomas
authors.initials: T
authors.lastname: Biederer
mesh_terms: D000818:Animals; D019556:COS Cells; D002448:Cell Adhesion / Q000502:physiology; D015816:Cell Adhesion Molecules, Neuronal / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002522:Chlorocebus aethiops; D018360:Crystallography, X-Ray; D006031:Glycosylation; D006801:Humans; D013058:Mass Spectrometry; D009154:Mutation; D019158:N-Acetylneuraminic Acid / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017729:Presynaptic Terminals / Q000737:chemistry* / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000502:physiology; D017434:Protein Structure, Tertiary
chemical_list: D015816:Cell Adhesion Molecules, Neuronal; D019158:N-Acetylneuraminic Acid