Thermodynamics Research Today is a free monthly online journal that collates and summarizes the latest research about Thermodynamics, including details on enthalpy, entropy, energy transitions. | ||||||||
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Structural, Thermodynamic, and Mutational Analyses of a Psychrotrophic RNase HI(,).Tadokoro T, You DJ, Abe Y, Chon H, Matsumura H, Koga Y, Takano K, Kanaya S Department of Material and Life Science and Department of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan, and CREST, JST, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan. Ribonuclease (RNase) HI from the psychrotrophic bacterium Shewanella oneidensis MR-1 was overproduced in Escherichia coli, purified, and structurally and biochemically characterized. The amino acid sequence of MR-1 RNase HI is 67% identical to that of E. coli RNase HI. The crystal structure of MR-1 RNase HI determined at 2.0 A resolution was highly similar to that of E. coli RNase HI, except that the number of intramolecular ion pairs and the fraction of polar surface area of MR-1 RNase HI were reduced compared to those of E. coli RNase HI. The enzymatic properties of MR-1 RNase HI were similar to those of E. coli RNase HI. However, MR-1 RNase HI was much less stable than E. coli RNase HI. The stability of MR-1 RNase HI against heat inactivation was lower than that of E. coli RNase HI by 19 degrees C. The conformational stability of MR-1 RNase HI was thermodynamically analyzed by monitoring the CD values at 220 nm. MR-1 RNase HI was less stable than E. coli RNase HI by 22.4 degrees C in Tm and 12.5 kJ/mol in DeltaG(H2O). The thermodynamic stability curve of MR-1 RNase HI was characterized by a downward shift and increased curvature, which results in an increased DeltaCp value, compared to that of E. coli RNase HI. Site-directed mutagenesis studies suggest that the difference in the number of intramolecular ion pairs partly accounts for the difference in stability between MR-1 and E. coli RNases HI. Published 19 June 2007 in Biochemistry, 46(25): 7460-8.
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