A novel glycine receptor beta subunit splice variant predicts an unorthodox transmembrane topology. Assembly into heteromeric receptor complexes.
The inhibitory glycine receptor is a ligand-gated ion channel with a pentameric assembly from ligand binding alpha and structural beta subunits. In addition to alpha subunit gene variants (alpha1-alpha4) and developmental alterations in subunit composition of the receptor protein complex, alternative splicing of alpha subunits has been found to contribute to glycine receptor heterogeneity. Here, we describe a novel splice variant of the glycine receptor beta subunit from mouse central nervous system, prevailing in macroglial cells, predominantly in astrocytes and extraneural tissues. As predicted by its cDNA sequence, the novel subunit betaDelta7 lacks amino acid positions 251-302 encoded by exon 7 of the Glrb gene. Transcripts and antigen of betaDelta7 were detected in cerebral cortex, liver, and heart. Lack of exon 7 results in a profoundly altered prediction of transmembrane topology as betaDelta7 lacks TM1 and TM2 present in the full-length variant. Despite these topological alterations, in vitro studies showed that the betaDelta7 polypeptide integrates into the plasma membrane, forming receptor complexes with the alpha1 subunit and gephyrin. Our data demonstrate that a topology deviating from the classical four transmembrane-fold is compatible with formation of glycine receptor protein complexes. However, co-expression of alpha1 with betaDelta7 subunits did not change glycine receptor channel properties. Rather, the high level of expression in non-neuronal cells having intimate contact with synaptic regions may account for a yet unknown function of this splice variant betaDelta7 in glycinergic neurotransmission.
Oertel
Jana
J
Institut für Biochemie, Emil-Fischer-Zentrum, Universität Erlangen-Nürnberg, Fahrstrasse 17, 91054 Erlangen, Germany.
Villmann
Carmen
C
Kettenmann
Helmut
H
Kirchhoff
Frank
F
Becker
Cord-Michael
CM
D000818:Animals; D001253:Astrocytes / Q000502:physiology; D001483:Base Sequence; D001921:Brain / Q000502:physiology; D002460:Cell Line; D002540:Cerebral Cortex / Q000502:physiology*; D017931:DNA Primers; D018076:DNA, Complementary / Q000235:genetics; D005091:Exons; D006321:Heart / Q000502:physiology; D006801:Humans; D007668:Kidney; D008099:Liver / Q000502:physiology; D051379:Mice; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D018009:Receptors, Glycine / Q000737:chemistry* / Q000235:genetics*; D011994:Recombinant Proteins / Q000737:chemistry; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017384:Sequence Deletion; D014158:Transcription, Genetic; D014162:Transfection
D017931:DNA Primers; D018076:DNA, Complementary; C491949:Glrb protein, mouse; D018009:Receptors, Glycine; D011994:Recombinant Proteins; D012313:RNA