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

- Solution structure of two C23O enzymes of different origin has been studied.
- Both C23Os present an impressive similarity in overall shape and functionality.
- Thermophilic C23O solution scattering is reproduced well from its crystal structure.
- Mesophilic C23O has a slightly extended shape in solution compared to crystal.
- Both C23Os have dramatically different thermostability and low sequence identity.

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.