Escherichia coli GlpE is a prototype sulfurtransferase for the single-domain rhodanese homology superfamily

Background: Rhodanese domains are structural modules occurring in the three major evolutionary phyla. They are found as single-domain proteins, as tan demly repeated modules in which the C-terminal domain only bears the proper ly structured active site, or as members of multidomain proteins. Although in vitro assays show sulfurtransferase or phosphatase activity associated w ith rhodanese or rhodanese-like domains, specific biological roles for most members of this homology superfamily have not been established. Results: Eight ORFs coding for proteins consisting of (or containing) a rho danese domain bearing the potentially catalytic Cys have been identified in the Escherichia coli K-12 genome. One of these codes for the 12-kDa protei n GlpE, a member of the sn-glycerol 3-phosphate (glp) regulon. The crystal structure of GlpE, reported here at 1.06 Angstrom resolution, displays alph a/beta topology based on five beta strands and five alpha helices. The GlpE catalytic Cys residue is persulfurated and enclosed in a structurally cons erved 5-residue loop in a region of positive electrostatic field. Conclusions: Relative to the two-domain rhodanese enzymes of known three-di mensional structure, GlpE displays substantial shortening of loops connecti ng alpha helices and beta sheets, resulting in radical conformational chang es surrounding the active site. As a consequence, GlpE is structurally more similar to Cdc25 phosphatases than to bovine or Azotobacter vinelandii rho daneses. Sequence searches through completed genomes indicate that GlpE can be considered to be the prototype structure for the ubiquitous single-doma in rhodanese module.