The human glycine receptor β subunit: primary structure, functional characterisation and chromosomal localisation of the human and murine genes

Abstract

The inhibitory glycine receptor (GlyR) is a pentameric receptor comprised of α and β subunits, of which the β subunit has not been characterised in humans. A 2106 bp cDNA, isolated from a human hippocampal cDNA library, contained an open reading frame of 497 amino acids which encodes the β subunit of the human GlyR. The mature human GlyR β polypeptide displays 99% amino acid identity with the rat GlyR β subunit and 48% identity with the human GlyR α1 subunit. Neither [3H]strychnine binding nor glycine-gated currents were detected when the human GlyR β subunit cDNA was expressed in the human embryonic kidney 293 cell line. However, co-expression of the β subunit cDNA with the α1 subunit cDNA resulted in expression of functional GlyRs which showed a 4-fold reduction in the EC50 values when compared to α1 homomeric GlyRs. Glycine-gated currents of α1/β GlyRs were 17-fold less sensitive than homomeric α1 GlyRs to the antagonists picrotoxin, picrotoxinin and picrotin, providing clear evidence that heteromeric α1/β GlyRs were expressed. The β subunit appears to play a structural rather than ligand binding role in GlyR function. Fluorescence in situ hybridisation was used to localise the gene encoding the human GlyR β subunit (GLRB) to chromosome 4q32, a position syntenic with mouse chromosome 3. In situ hybridisation using the human GlyR β subunit cDNA showed that the murine GlyR β subunit gene (Glrb) maps to the spastic (spa) locus on mouse chromosome 3 at bands E3–F1. This is consistent with the recent finding that a mutation in the murine GlyR β subunit causes the spa phenotype. It also raises the possibility that mutations in the human β subunit gene may cause inherited disorders of the startle response.