Metal ion induced allosteric transition in the catalytic activity of an artificial phosphodiesterase

Abstract

An artificial phosphodiesterase (1) bearing two types of metal binding sites, a catalytic site and a regulatory bipyridine site showed a unique allosteric transition in the catalytic activity against the metal concentration. The rate constants for the hydrolysis reaction of 2-hydroxypropyl-p-nitrophenyl phosphate (HPNP) and RNA dimer (ApA) with and without an effector metal ion were evaluated; the k_obs value of HPNP hydrolysis for 1·(Zn²⁺)₃ (2.0 × 10⁻⁴ s⁻¹) is 3.3 times larger than that for 1·(Zn²⁺)₂. In the case of 1 and Cu²⁺, a 19.4 times larger k_obs value was obtained for 1·(Cu²⁺)₃ (1.2 × 10⁻³ s⁻¹) against 1·(Cu²⁺)₂. The increase in the catalytic activity is ascribed to the allosteric conformational transition of 1 induced by the coordination of effector metal ion to the Bpy moiety. A detailed investigation revealed that a conformational change of 1 induced by the third M²⁺ complexation enhances the rate of hydrolysis rather than a change in the substrate affinity.