title: An IRBIT homologue lacks binding activity to inositol 1,4,5-trisphosphate receptor due to the unique N-terminal appendage.
abstract: IRBIT is an inositol 1,4,5-trisphosphate (IP(3)) receptor (IP(3)R)-binding protein that inhibits the activation of IP(3)R by competing with IP(3) for the common binding site on IP(3)R. In this study, we characterize an IRBIT homologue, termed Long-IRBIT. Long-IRBIT is highly homologous to IRBIT ( approximately 88%) and heteromerizes with IRBIT. In spite of complete conservation of critical amino acids required for the interaction with IP(3)R and comparable phosphorylations on critical four Ser residues for IP(3)R-binding, Long-IRBIT retains little ability to interact with IP(3)R. Deletion mutagenesis analysis revealed that this low affinity to IP(3)R is attributable to an inhibitory effect of the Long-IRBIT specific N-terminal appendage (LISN domain). Immunohistochemical analysis revealed the distinct distribution of Long-IRBIT and IRBIT in mouse cerebellar cortex, that is, Long-IRBIT is mainly expressed in interneurons such as basket cells, while IRBIT is mainly expressed in glial cells. Furthermore, Long-IRBIT, but not IRBIT, underwent phosphorylation during neuronal differentiation in neuroblastoma cells and this phosphorylation was dependent on the LISN domain. These results suggest that Long-IRBIT has a different function from IRBIT.
authors.affiliation: International Cooperative Research Project-Solution Oriented Research for Science and Technology, Japan Science and Technology Agency, Saitama, Japan.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Ando
authors.forename: Akihiro
authors.initials: A
authors.lastname: Mizutani
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Mikoshiba
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive / Q000235:genetics; D019556:COS Cells; D002522:Chlorocebus aethiops; D017353:Gene Deletion; D006367:HeLa Cells; D006801:Humans; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000737:chemistry / Q000378:metabolism*; D037181:Lectins, C-Type / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010446:Peptide Fragments / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D017386:Sequence Homology, Amino Acid
chemical_list: C470184:CLECL1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D037181:Lectins, C-Type; D008565:Membrane Proteins; D010446:Peptide Fragments