J Neurochem 2007 Dec 01;1036:2556-64. doi: 10.1111/j.1471-4159.2007.04982.x.

Replacement of histidine in position 105 in the α₅ subunit by cysteine stimulates zolpidem sensitivity of α₅β₂γ₂ GABA(A) receptors.

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Zolpidem is a positive allosteric modulator of GABA(A) receptors with sensitivity to subunit composition. While it acts with high affinity and efficacy at GABA(A) receptors containing the α(1) subunit, it has a lower affinity to GABA(A) receptors containing α(2) , α(3) , or α(5) subunits and has a very weak efficacy at receptors containing the α(5) subunit. Here, we show that replacing histidine in position 105 in the α(5) subunit by cysteine strongly stimulates the effect of zolpidem in receptors containing the α(5) subunit. The side chain volume of the amino acid residue in this position does not correlate with the modulation by zolpidem. Interestingly, serine is not able to promote the potentiation by zolpidem. The homologous residues to α(5) H105 in α(1) , α(2) , and α(3) are well-known determinants of the action of classical benzodiazepines. Other studies have shown that replacement of these histidines α(1) H101, α(2) H101, and α(3) H126 by arginine, as naturally present in α(4) and α(6) , leads to benzodiazepine insensitivity of these receptors. Thus, the nature of the amino acid residue in this position is not only crucial for the action of classical benzodiazepines but in α(5) containing receptors also for the action of zolpidem.

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