title: The sulfur oxygenase reductase from the mesophilic bacterium Halothiobacillus neapolitanus is a highly active thermozyme.
abstract: A biochemical, biophysical, and phylogenetic study of the sulfur oxygenase reductase (SOR) from the mesophilic gammaproteobacterium Halothiobacillus neapolitanus (HnSOR) was performed in order to determine the structural and biochemical properties of the enzyme. SOR proteins from 14 predominantly chemolithoautotrophic bacterial and archaeal species are currently available in public databases. Sequence alignment and phylogenetic analysis showed that they form a coherent protein family. The HnSOR purified from Escherichia coli after heterologous gene expression had a temperature range of activity of 10 to 99°C with an optimum at 80°C (42 U/mg protein). Sulfite, thiosulfate, and hydrogen sulfide were formed at various stoichiometries in a range between pH 5.4 and 11 (optimum pH 8.4). Circular dichroism (CD) spectroscopy and dynamic light scattering showed that the HnSOR adopts secondary and quaternary structures similar to those of the 24-subunit enzyme from the hyperthermophile Acidianus ambivalens (AaSOR). The melting point of the HnSOR was ≈20°C lower than that of the AaSOR, when analyzed with CD-monitored thermal unfolding. Homology modeling showed that the secondary structure elements of single subunits are conserved. Subtle changes in the pores of the outer shell and increased flexibility might contribute to activity at low temperature. We concluded that the thermostability was the result of a rigid protein core together with the stabilizing effect of the 24-subunit hollow sphere.
authors.affiliation: Institute of Microbiology and Genetics, Technische Universität Darmstadt, Darmstadt, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Veith
authors.forename: Hugo M
authors.initials: HM
authors.lastname: Botelho
authors.forename: Florian
authors.initials: F
authors.lastname: Kindinger
authors.forename: Cláudio M
authors.initials: CM
authors.lastname: Gomes
authors.forename: Arnulf
authors.initials: A
authors.lastname: Kletzin
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004795:Enzyme Stability; D044222:Halothiobacillus / Q000737:chemistry / Q000145:classification / Q000201:enzymology* / Q000235:genetics; D006358:Hot Temperature; D008958:Models, Molecular; D008969:Molecular Sequence Data; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny
chemical_list: D001426:Bacterial Proteins; D050862:Oxidoreductases Acting on Sulfur Group Donors