Dsb proteins control the formation and rearrangement of disulfide bonds during the folding of membrane and exported proteins. DsbA is an oxidant that catalyzes formation of disulfide bonds in newly synthesized, and yet unfolded proteins. In order to act catalytically again, it has to be reoxidized by a transmembrane protein DsbB characterized by two pairs of disulfides. DsbB is related to another protein family Dsbl, characterized by the presence of only one disulfide, and an additional C-terminal beta-propeller domain. The protein AAN82231 from E. coli strain CFT073 has been recently described as a new member of the Dsbl family (Grimshaw et al., 2008). It was found that AAN82231 forms a functional redox pair with DsbL - a newly described DsbA-like protein. Here, we report that AAN82231 shares no characteristic features with the Dsbl proteins. Instead, according to phylogenetic analyses AAN82231 clearly belongs to another, previously described subfamily of DsbB paralogs. To facilitate classification of DsbB and Dsbl homologs, we propose a new nomenclature system and present an updated phylogenetic analysis of the DsbB superfamily, which comprises the following families: "orthodox" DsbB, its paralogs now named DsbB2 (including AAN82231), Dsbl and two groups of so far uncharacterized DsbB paralogs termed DsbB3 and DsbB4. We have also developed a web server dedicated to phylogenetic assignment of DsbB/Dsbl candidate proteins that will be identified in the future.
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