Alcohol modulation of G-protein-gated inwardly rectifying potassium channels: from binding to therapeutics

Abstract

Alcohol (ethanol)-induced behaviors may arise from direct interaction of alcohol with discrete protein cavities within brain proteins. Recent structural and biochemical studies have provided new insights into the mechanism of alcohol-dependent activation of G protein-gated inwardly rectifying potassium (GIRK) channels, which regulate neuronal responses in the brain reward circuit. GIRK channels contain an alcohol binding pocket formed at the interface of two adjacent channel subunits. Here, we discuss the physiochemical properties of the alcohol pocket and the roles of G protein βγ subunits and membrane phospholipid PIP2 in regulating the alcohol response of GIRK channels. Some of the features of alcohol modulation of GIRK channels may be common to other alcohol-sensitive brain proteins. We discuss the possibility of alcohol-selective therapeutics that block alcohol access to the pocket. Understanding alcohol recognition and modulation of brain proteins is essential for development of therapeutics for alcohol abuse and addiction.

PIP2 and PIP3 interact with N-terminus region of TRPM4 channel

“…Positively charged amino acids are frequent in the vicinity of the inner plasma membrane leaflet where binding sites for regulatory molecules such as phosphatidylinositol phosphates are expected to be abundant. Their mutation to alanine residues causes a replacement of their charged-side chains in the binding site, which makes it less favorable for interaction with PIP2 [67][68][69]. According to this hypothesis, our in silico predictions support that R755A and R767A mutations result in the loss of non-covalent interactions with the phosphate groups of PIP2/PIP3 which is in agreement with our experimental data.…”

GIRK Channels

“…However, the recent development of GIRK channel subtype-selective modulators that can be systemically administered have opened up new possibilities for GIRK channels as therapeutic targets Wen et al, 2013;Wydeven et al, 2014). In agreement with previous work, we propose that GIRK channels represent a novel and potentially highly effective route for the treatment of addiction disorders (Bodhinathan & Slesinger, 2014;Lujan, Marron Fernandez de Velasco, Aguado, & Wickman, 2014; and may be particularly useful when combined with cognitive behavioral therapy to help reduce the ability of drugassociated cues to induce relapse (McCusker, 2001).…”

The Roles of Gβγ and Gα in Gating and Regulation of GIRK Channels

“…Notably, in the GIRK2 C321V mutant, both I basal , Gβγ-and ethanol-dependent activation remained intact (Clancy et al, 2005). In GIRK2, both I basal and ethanol activation are largely Gβγ-independent (Bodhinathan & Slesinger, 2014;Rubinstein et al, 2009). Taken together, these findings suggest that the GIRK2 C321V channel is functional and that Gβγ gating is intact, and point to a specific role for Gα in GPCR-induced GIRK2 activation by the heterotrimeric Gαβγ (Clancy et al, 2005).…”

“…I basal and I evoked are sensitively regulated by the availability of Gα GDP , whereas recruitment of Gβγ ensures high level of activity of the channel under variable circumstances. The substantial level of I basal of GIRK1/2 renders this channel with the property of bidirectional regulator which has been hypothesized to sensitively regulate neuronal excitability (Rubinstein et al, 2007): a decrease in I basal (e.g., by activation of G q -coupled GPCR) would increase the excitability, and channel activation by G i -coupled GPCRs or drugs such as lithium (Farhy Tselnicker et al, 2014) or ethanol (Bodhinathan & Slesinger, 2014) will have an opposite effect. In comparison, homomeric GIRK2 channels, with their low I basal and high sensitivity to Gβγ, are more suitable to serve as sensitive but mostly unidirectional, low-noise transduces of inhibitory neurotransmitter actions (Rubinstein et al, 2009).…”

“…Additional levels of versatility and complexity, discussed elsewhere, are added by the regulation or modulation of the channel by its direct interaction with G protein receptor kinases (Raveh, Cooper, GuyDavid, & Reuveny, 2010), alcohols (Bodhinathan & Slesinger, 2014;Kobayashi et al, 1999;Lewohl et al, 1999), and additional factors such as metabolites of arachidonic acid (Rogalski & Chavkin, 2001). Furthermore, the gating or interaction with Gβγ are regulated by direct phosphorylation by serine/threonine protein kinase A (PKA) (Medina et al, 2000;Mullner et al, 2000) and protein kinase C (PKC) (Hill & Peralta, 2001;Sharon et al, 1997;Stevens, Shah, Pinnock, & Lee, 1999), and by tyrosine phosphorylation (Ippolito, Temkin, Rogalski, & Chavkin, 2002;Rogalski, Appleyard, Pattillo, Terman, & Chavkin, 2000).…”