Residues in the 1st Transmembrane-Spanning Helix Are Important for GABA[sub.A]Iρ/I Receptor Function

• Published in: Biomolecules (Basel, Switzerland) Switzerland), 2022-09, Vol.12 (9)
• Main Authors: Crowther, Kate M, Mesoy, Susanne M, Lummis, Sarah C. R
• Format: Article
• Language: English
• Subjects: Cell receptors; GABA; Health aspects
• ISSN: 2218-273X; 2218-273X
• DOI: 10.3390/biom12091251

GABA[sub.A] ρ receptors are a subfamily of the GABA[sub.A] receptor family of pentameric ligand-gated ion channels (pLGICs). Each subunit has a common structure, including a transmembrane domain of four α-helices (M1–M4). The aim of this study was to identify important M1 residues in the GABA[sub.A] ρ receptor (GABA[sub.A] ρR), 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[sub.A] ρR function. Further mutations reveal the properties that are important for function in critical residues, and, using a GABA[sub.A] ρR homology model, we suggest amino acid interactions that could be important. Phylogenetic analysis comparing GABA[sub.A] R and other pLGICs subunits reveals most M1 residue properties linked to GABA[sub.A] ρR function are ancestrally ancient, but some are more recent acquisitions. Multiple sequence alignment of M1 residues across GABA[sub.A] R subunits reveal three residues are well conserved except in GABA[sub.A] R α subunits. Substitution of ρ1 subunit residues to their α1 subunit equivalents showed one alters functional parameters. Overall, the data provide a comprehensive picture of M1 residues that contribute to GABA[sub.A] ρR function, and illustrate how they might do so.