A transthyretin-related protein is functionally expressed in Herbaspirillum seropedicae.
Transthyretin-related proteins (TRPs) constitute a family of proteins structurally related to transthyretin (TTR) and are found in a large range of bacterial, fungal, plant, invertebrate, and vertebrate species. However, it was recently recognized that both prokaryotic and eukaryotic members of this family are not functionally related to transthyretins. TRPs are in fact involved in the purine catabolic pathway and function as hydroxyisourate hydrolases. An open reading frame encoding a protein similar to the Escherichia coli TRP was identified in Herbaspirillum seropedicae genome (Hs_TRP). It was cloned, overexpressed in E. coli, and purified to homogeneity. Mass spectrometry data confirmed the identity of this protein, and circular dichroism spectrum indicated a predominance of beta-sheet structure, as expected for a TRP. We have demonstrated that Hs_TRP is a 5-hydroxyisourate hydrolase and by site-directed mutagenesis the importance of three conserved catalytic residues for Hs_TRP activity was further confirmed. The production of large quantities of this recombinant protein opens up the possibility of obtaining its 3D-structure and will help further investigations into purine catabolism.