Abstract
GABAA receptors are believed to be heteropentamers that can be constructed from six subunit classes: α(1–6), β(1–4), γ(1–3), δ, ε, and π. Given that individual neurons often express multiple receptor subunits, it is important to understand how these receptors assemble. To determine which domains of receptor subunits control assembly, we have exploited the differing capabilities of the β2 and β3 subunits to form functional cell surface homomeric receptors. Using a chimeric approach, we have identified four amino acids in the N-terminal domain of the β3 subunit that mediate functional cell surface expression of this subunit compared with β2, which is retained within the endoplasmic reticulum. Substitution of these four amino acids—glycine 171, lysine 173, glutamate 179, and arginine 180—into the β2 subunit was sufficient to enable the β2 subunit to homo-oligomerize. The effect of this putative “assembly signal” on the production of heteromeric receptors composed of αβ and βγ subunits was also analyzed. This signal was not critical for the formation of receptors composed of either α1β2 or α1β3 subunits, suggesting that mutation of these residues did not disrupt subunit folding. However, this signal was important in the formation of βγ2 receptors. These residues did not seem to affect the initial association of β2 and γ2 subunits but appeared to be important for the subsequent production of functional receptors. Our studies identify, for the first time, key residues within the N-terminal domains of receptor β subunits that mediate the selective assembly of GABAA receptors.