Modeling and analysis of the structure of the thermostable catechol 2,3-dioxygenase from Bacillus Stearothermophilus

Correlation of thermostability and conformational changes of catechol 2, 3-dioxygenases from two disparate micro-organisms

We have investigated the structure of recombinant catechol 2, 3-dioxygenase (C23O) purified from two species in which the enzyme has evolved to function at different temperature. The two species are mesophilic bacterium Pseudomonas putida strain mt-2 and thermophilic archaea Sulfolobus acidocaldariusDSM639. Using the primary sequence analysis, we show that both C23Os have only 30% identity and 48% similarity but contain conserved amino acid residues forming an active site area around the iron ion. The corresponding differences in homology, but structural similarity in active area residues, appear to provide completely different responses to heating the two enzymes. We confirm this by small angle X-ray scattering and demonstrate that the overall structure of C23O from P. putida is slightly different from its crystalline form whereas the solution scattering of C23O from S. acidocaldarius at temperatures between 4 and 85°C ideally fits the calculated scattering from the single crystal structure. The thermostability of C23O from S. acidocaldarius correlates well with conformation in solution during thermal treatment. The similarity of the two enzymes in primary and tertiary structure may be taken as a confirmation that two enzymes have evolved from a common ancestor.

The Mechanism of TC230′s Thermostability: A Molecular Dynamics Simulation Study

The quasielastic neutron scattering index beta and the modulus of a protein's quasi-electric dipole moment were utilized to quantitate the thermostability of wildtype TC23O and its mutants. Charged residues Arg314, Glu246, Glu291, and some prolines near the C-terminus of the sequence (Pro228, Pro296, and Pro308) were identified to be critical for the thermostability of wildtype TC23O according to these two criteria. By analyzing the molecular conformation changes during the simulation, it was demonstrated how the mutant P228S was destabilized by disrupting two salt-bridges Asp116OD1-Lys215N and Glu210OE1-Lys217N at an adjacent beta-turn. The destabilization of P296S also shown to be intimate correlated with the break down of ion pair Lys188N-Glu291OE1. The sensitivity of its electrostatic network to the local structure is an important feature. It reveals that the 'proline effect' and electrostatic interactions together influences the thermostability of TC23O a lot.

Thermostability of Protein Studied by Molecular Dynamics Simulation

The thermostability of protein thermostable cathechol 2,3-dixoygenase (TC23O) has been studied by the parallel molecular dynamics simulations. By analysis of the exponent beta, which is related to the scattering spectrum and constant-pressure heat capacity Cp, we reveal the respective contribution of a specific residue 228 proline; a specific salt bridge, Lys188N-Glu291OE1; four ions; and a different water environment to the thermostability of TC23O. The dynamic transition temperature of the mutants, Pro228Ser and Glu291Gly of the TC23O, was decreased about 10 degrees C and 19 degrees C respectively. The displacement of the four ions had no significant effect on the thermostability of TC23O. Water affects the thermostability by influencing the changes of accessible conformation to a certain extent. All these results agree with the known experimental results.