Gタンパク質活性化に及ぼすクロライドイオンの効果

クロライドイオンとシグナルトランスダクション

抄録

G proteins act as signal transducers that couple receptors to effectors through membranes. G proteins are in a GDP-bound form in the basal state, which can interact with receptors. The hormone-bound receptor promotes GDP-GTP exchange of G proteins. The GTP, Mg²⁺-bound G proteins can activate effector molecules, which in turn produce second messengers. The GTP, Mg²⁺-form is converted to the GDP-form by the GTP-hydrolysis activity of G protein α-subunits. Cl^- ions modulate the GDP-GTP cycle of G proteins. Cl^- ions, in the presence of Mg²⁺, decelerate the receptor-independent spontaneous release of GDP (ca. 6-fold by 100 mM NaCl), which will result in a lowering of the basal level of second messengers. On the other hand, the GTP-hydrolysis activity of G proteins was suppressed by 3-fold with 100 mM NaCl, which will result in keeping the G proteins in an active form for a longer time. In the absence of Mg²⁺, Cl^- ion mimics Mg²⁺ to convert GTP-bound G proteins to an active form (dissociated form), although the effects are weaker than those of Mg²⁺. These effects are very different from F^-, which is another halogen ion that interacts with G proteins.