Abstract
Thioredoxin is a small ubiquitous protein that is involved in the dithiol-disulfide exchange reaction, by way of two cysteine residues located on the molecule surface. In order to elucidate the role of thioredoxin in Chlorobaculum tepidum, an anaerobic green sulfur bacterium that uses various inorganic sulfur compounds as an electron donor under strict anaerobic conditions for growth, we applied the thioredoxin affinity chromatography method. In this study, 37 cytoplasmic proteins were captured as thioredoxin target candidates, including proteins involved in sulfur assimilation. Furthermore, six of the candidate proteins were members of the reductive tricarboxylic acid cycle. The redox sensitivity of three of them was examined: citrate lyase, citrate synthase, and malate dehydrogenase, using their recombinant proteins. Based on the information relating to the target proteins, the significance of thioredoxin as a reductant for the metabolic pathway in the anaerobic photosynthetic bacteria is discussed.
