PNNL

Abstract

Cat scratch fever (aka cat scratch disease and Bartonellosis) is an infectious disease caused by the proteobacterium Bartonella henselae following a cat scratch. Although the infection is usually resolved spontaneously without treatment in healthy adults, Bartonellosis may lead to severe complications in young children and immunocompromised patients and there is new evidence suggesting B. henselae may be associated with a broader range of clinical symptoms then previously believed. The genome of B. henselae contains the genes for two putative Nudix hydrolyases, BH02020 and BH01640, proteins that regulate the intracellular concentration of nucleotide cofactors and signaling molecules. The amino acid sequence of BH02020 is similar to the prototypical member of the Nudix superfamily, Escherichia coli MutT, a protein best known for its ability to neutralize the promutagenic compound 7,8-dihydro-8-oxoguanosine triphosphate. Here we report the crystal structure for BH02020, Bh-MutT, in the Mg2+ bound form at 2.1 Å resolution (3HHJ). As observed for all Nudix hydroylase structures, the a-helix of the highly conserved "Nudix box" in Bh-MutT is one of two helices that sandwich a "four-strand" mixed ß-sheet with the central two ß-strands parallel to each other. The catalytically essential divalent cation observed in the Bh-MutT structure, Mg2+, is coordinated to the side chains of E57 and E61. A temperature melt obtained with circular dichroism spectroscopy shows that Bh-MutT irreversible unfolds and precipitates out of solution upon heating with a Tm of 60°C.