Figure 7. Amino acid sequences.

Above, cartoon of the general primary structure of GABA_A receptor subunits showing amino and carboxy termini, and four transmembrane spanning regions (shaded). The extracellular amino domain contains a cysteine loop (C-C). Lines indicate approximate location of amino acid sequences shown below. Region of protein involved in co-ordinating Zn²⁺ binding is putatively extracellular. Below, comparison of amino acid sequences of GABA_A receptor subunits with homologous residues in the neighborhood of a ρ1 histidine (156) on extracellular amino terminus that is critical to Zn²⁺ inhibition of GABA_C receptors (Wang et al. 1995). Amino acids are in three letter code and numbers refer to the codons of the predicted amino acid sequence of the full-length cDNA where the canonical methionine is codon 1. Arrow marks the location of the critical histidine (emboldened) of ρ1. Box encloses adjoining location on GABA_A subunits that contains a histidine (emboldened) residue on the α1-, a neutral leucine on β2-, and a positively charged arginine on the γ2-subunit.