title: SAP97 blocks the RXR ER retention signal of NMDA receptor subunit GluN1-3 through its SH3 domain.
abstract: SAP97 is directly involved in exporting NMDA receptors with a specific subunit composition from the endoplasmic reticulum (ER). Characterization of the interactions between SAP97 and an NMDA receptor splice variant, GluN1-3, and of the effects on forward trafficking revealed that an ER-level interaction blocked the RXR ER-retention motif in the GluN1-3 cytoplasmic C-terminus in the context of both reporter molecules and full-length receptors. Binding of SAP97 to the PDZ-binding domain of GluN1-3 was required, but the blockade of ER-retention was mediated by the SH3-GuK domains coupled with the action of the N-terminus of SAP97. While other domains of SAP97 were involved in forward trafficking of GluN1-3 out of the ER, the SH3 domain was necessary and sufficient to block the ER retention. This is the first direct evidence for the masking of ER-retention signals by PDZ domain-containing proteins, and provides detailed underlying mechanistic requirements. Such a mechanism could be central to modulating the ER exit of receptors into local, non-conventional or conventional, secretory pathways in neurons.
authors.affiliation: Graduate College of Biomedical Sciences, Western University of Health Sciences, 701 E. Second Street, Pomona, CA 91766, USA.
authors.forename: Xiaoqi
authors.initials: X
authors.lastname: Hong
authors.affiliation: Graduate College of Biomedical Sciences, Western University of Health Sciences, 701 E. Second Street, Pomona, CA 91766, USA.
authors.forename: Mariam
authors.initials: M
authors.lastname: Avetisyan
authors.affiliation: Graduate College of Biomedical Sciences, Western University of Health Sciences, 701 E. Second Street, Pomona, CA 91766, USA.
authors.forename: Mason
authors.initials: M
authors.lastname: Ronilo
authors.affiliation: Graduate College of Biomedical Sciences, Western University of Health Sciences, 701 E. Second Street, Pomona, CA 91766, USA. Electronic address: sstandley@westernu.edu.
authors.forename: Steve
authors.initials: S
authors.lastname: Standley
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism; D002522:Chlorocebus aethiops; D000074288:Discs Large Homolog 1 Protein; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate / Q000737:chemistry* / Q000378:metabolism*; D047488:Retinoid X Receptors / Q000378:metabolism*; D013329:Structure-Activity Relationship; D018909:src Homology Domains
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C513314:DLG1 protein, human; D000074288:Discs Large Homolog 1 Protein; D008565:Membrane Proteins; D021122:Protein Subunits; D016194:Receptors, N-Methyl-D-Aspartate; D047488:Retinoid X Receptors; D049452:Green Fluorescent Proteins
keywords: NMDA; PDZ domain; RXR motif; Receptor; SAP97; SH3 domain; Trafficking