title: Short-chain dehydrogenases/reductases in cyanobacteria.
abstract: The short-chain dehydrogenases/reductases (SDRs) represent a large superfamily of enzymes, most of which are NAD(H)-dependent or NADP(H)-dependent oxidoreductases. They display a wide substrate spectrum, including steroids, alcohols, sugars, aromatic compounds, and xenobiotics. On the basis of characteristic sequence motifs, the SDRs are subdivided into two main (classical and extended) and three smaller (divergent, intermediate, and complex) families. Despite low residue identities in pairwise comparisons, the three-dimensional structure among the SDRs is conserved and shows a typical Rossmann fold. Here, we used a bioinformatics approach to determine whether and which SDRs are present in cyanobacteria, microorganisms that played an important role in our ecosystem as the first oxygen producers. Cyanobacterial SDRs could indeed be identified, and were clustered according to the SDR classification system. Furthermore, because of the early availability of its genome sequence and the easy application of transformation methods, Synechocystis sp. PCC 6803, one of the most important cyanobacterial strains, was chosen as the model organism for this phylum. Synechocystis sp. SDRs were further analysed with bioinformatics tools, such as hidden Markov models (HMMs). It became evident that several cyanobacterial SDRs show remarkable sequence identities with SDRs in other organisms. These so-called 'homologous' proteins exist in plants, model organisms such as Drosophila melanogaster and Caenorhabditis  elegans, and even in humans. As sequence identities of up to 60% were found between Synechocystis and humans, it was concluded that SDRs seemed to have been well conserved during evolution, even after dramatic terrestrial changes such as the conversion of the early reducing atmosphere to an oxidizing one by cyanobacteria.
authors.affiliation: University Medical School Schleswig-Holstein Campus Kiel, Institute of Toxicology and Pharmacology for Natural Scientists, Schleswig-Holstein, Germany.
authors.forename: Anneke
authors.initials: A
authors.lastname: Kramm
authors.forename: Michael
authors.initials: M
authors.lastname: Kisiela
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Schulz
authors.forename: Edmund
authors.initials: E
authors.lastname: Maser
mesh_terms: D019295:Computational Biology; D000458:Cyanobacteria / Q000201:enzymology*; D004269:DNA, Bacterial / Q000737:chemistry; D019143:Evolution, Molecular; D064429:Fatty Acid Synthases / Q000737:chemistry* / Q000378:metabolism; D016680:Genome, Bacterial; D008390:Markov Chains; D009247:NADH, NADPH Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D013379:Substrate Specificity; D046939:Synechocystis / Q000201:enzymology*
chemical_list: D004269:DNA, Bacterial; D010088:Oxidoreductases; C036543:short chain trans-2-enoyl-CoA reductase; D009247:NADH, NADPH Oxidoreductases; D064429:Fatty Acid Synthases