Enhancement of nuclease P1 activity in low concentration of denaturants

Perchlorate salts confer psychrophilic characteristics in α-chymotrypsin

Studies of salt effects on enzyme activity have typically been conducted at standard temperatures and pressures, thus missing effects which only become apparent under non-standard conditions. Here we show that perchlorate salts, which are found pervasively on Mars, increase the activity of α-chymotrypsin at low temperatures. The low temperature activation is facilitated by a reduced enthalpy of activation owing to the destabilising effects of perchlorate salts. By destabilising α-chymotrypsin, the perchlorate salts also cause an increasingly negative entropy of activation, which drives the reduction of enzyme activity at higher temperatures. We have also shown that α-chymotrypsin activity appears to exhibit an altered pressure response at low temperatures while also maintaining stability at high pressures and sub-zero temperatures. As the effects of perchlorate salts on the thermodynamics of α-chymotrypsin's activity closely resemble those of psychrophilic adaptations, it suggests that the presence of chaotropic molecules may be beneficial to life operating in low temperature environments.

Phosphate mono- and diesterase activities of the trinuclear zinc enzyme nuclease P1--insights from quantum chemical calculations

Nuclease P1 is a trinuclear zinc enzyme that catalyzes the hydrolysis of single-stranded DNA and RNA. Density functional calculations are used to elucidate the reaction mechanism of this enzyme with a model of the active site designed on the basis of the X-ray crystal structure. 2-Tetrahydrofuranyl phosphate and methyl 2-tetrahydrofuranyl phosphate substrates are used to explore the phosphomonoesterase and phosphodiesterase activities of this enzyme, respectively. The calculations reveal that for both activities, a bridging hydroxide performs an in-line attack on the phosphorus center, resulting in inversion of the configuration. Simultaneously, the P-O bond is cleaved, and Zn2 stabilizes the negative charge of the leaving alkoxide anion and assists its departure. All three zinc ions, together with Arg48, provide electrostatic stabilization to the penta-coordinated transition state, thereby lowering the reaction barrier.