Residues in the 1st Transmembrane-Spanning Helix Are Important for GABAAρ Receptor Function

GABA(A rho )receptors are a subfamily of the GABA(A) receptor family of pentameric ligand-gated ion channels (pLGICs). Each subunit has a common structure, including a transmembrane domain of four alpha-helices (M1-M4). The aim of this study was to identify important M1 residues in the GABA(A rho )receptor (GABA(A rho)R), using mutagenesis and functional assays combined with bioinformatic approaches. Alanine substitution of 12 of the 23 M1 residues yielded receptors with altered functional parameters, indicating these residues contribute to GABA(A rho)R function. Further mutations reveal the properties that are important for function in critical residues, and, using a GABA(A rho)R homology model, we suggest amino acid interactions that could be important. Phylogenetic analysis comparing GABA(A rho)R and other pLGICs subunits reveals most M1 residue properties linked to GABA(A rho)R function are ancestrally ancient, but some are more recent acquisitions. Multiple sequence alignment of M1 residues across GABA(A rho)R subunits reveal three residues are well conserved except in GABA(A rho)R alpha subunits. Substitution of rho 1 subunit residues to their alpha 1 subunit equivalents showed one alters functional parameters. Overall, the data provide a comprehensive picture of M1 residues that contribute to GABA(A rho)R function, and illustrate how they might do so.

Automated summary

This study identified the important M1 residues in GABA(A rho) receptors using mutagenesis and functional assays. The results provide insights into the functional properties of these residues and their differences among subunits. These findings are significant for understanding the mechanism of GABA(A rho) receptor function.