title: An intracellular domain with a novel sequence regulates cell surface expression and synaptic clustering of leucine-rich repeat transmembrane proteins in hippocampal neurons.
abstract: Leucine-rich repeat transmembrane proteins (LRRTMs) are single-spanning transmembrane proteins that belong to the family of synaptically localized adhesion molecules that play various roles in the formation, maturation, and function of synapses. LRRTMs are highly localized in the post-synaptic density; however, the mechanisms and significance of LRRTM synaptic clustering remain unclear. Here, we focus on the intracellular domain of LRRTMs and investigate its role in cell surface expression and synaptic clustering. The deletion of 55-56 residues in the cytoplasmic tail caused significantly reduced synaptic clustering of LRRTM1-4 in rat hippocampal neurons, whereas it simultaneously resulted in augmented LRRTM1-2 cell surface expression. A series of deletions and further single amino acid substitutions in the intracellular domain of LRRTM2 demonstrated that a previously uncharacterized sequence at the region of -16 to -13 from the C-terminus was responsible for efficient synaptic clustering and proper cell surface trafficking of LRRTMs. Furthermore, the clustering-deficient LRRTM2 mutant lost the ability to promote the accumulation of post-synaptic density protein-95 (PSD-95). These results suggest that trafficking to the cell surface and synaptic clustering of LRRTMs are regulated by a specific mechanism through this novel sequence in the intracellular domain that underlies post-synaptic molecular assembly and maturation. Leucine-rich repeat transmembrane proteins (LRRTMs) are synaptic cell adhesion molecules promoting synapse formation. LRRTMs are highly localized in the postsynaptic density. We report amino acid sequence YxxC in the intracellular domain of LRRTMs is responsible for the postsynaptic localization of LRRTMs. This novel amino acid sequence of LRRTMs facilitates synapse maturation. We propose this regulated synaptic clustering of LRRTMs by the intracellular domain presents a novel molecular mechanism of synapse maturation.
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Japan.
authors.forename: Keiichiro
authors.initials: K
authors.lastname: Minatohara
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Japan.
authors.forename: Yasunobu
authors.initials: Y
authors.lastname: Murata
authors.affiliation: Department of Basic Medicinal Sciences, Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, Japan.|Cellular and Structural Physiology Institute, Nagoya University, Nagoya, Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Fujiyoshi
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Japan.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Doi
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D002645:Chickens; D057809:HEK293 Cells; D006624:Hippocampus / Q000378:metabolism*; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism*; D000090263:Leucine-Rich Repeat Proteins; D008565:Membrane Proteins; D051379:Mice; D009419:Nerve Tissue Proteins; D019006:Neural Cell Adhesion Molecules / Q000096:biosynthesis / Q000235:genetics; D009474:Neurons / Q000378:metabolism*; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013569:Synapses / Q000235:genetics / Q000378:metabolism*
chemical_list: C561491:LRRTM2 protein, mouse; D000090263:Leucine-Rich Repeat Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D019006:Neural Cell Adhesion Molecules; D011506:Proteins
keywords: membrane protein; post-synaptic density; protein targeting; synapse formation; synaptic adhesion molecules