Structural characterization of CA1462, the Candida albicans thiamine pyrophosphokinase

Abstract

BACKGROUND: In search of new antifungal targets of potential interest for pharmaceutical companies, we initiated a comparative genomics study to identify the most promising protein-coding genes in fungal genomes. One criterion was the protein sequence conservation between reference pathogenic genomes. A second criterion was that the corresponding gene in Saccharomyces cerevisiae should be essential. Since thiamine pyrophosphate is an essential product involved in a variety of metabolic pathways, proteins responsible for its production satisfied these two criteria. RESULTS: We report the enzymatic characterization and the crystallographic structure of the Candida albicans Thiamine pyrophosphokinase. The protein was co-crystallized with thiamine or thiamine-PNP. CONCLUSION: The presence of an inorganic phosphate in the crystallographic structure opposite the known AMP binding site relative to the thiamine moiety suggests that a second AMP molecule could be accommodated in the C. albicans structure. Together with the crystallographic structures of the enzyme/substrate complexes this suggests the existence of a secondary, less specific, nucleotide binding site in the Candida albicans thiamine pyrophosphokinase which could transiently serve during the release or the binding of ATP. The structures also highlight a conserved Glutamine residue (Q138) which could interact with the ATP alpha-phosphate and act as gatekeeper. Finally, the TPK/Thiamine-PNP complex is consistent with a one step mechanism of pyrophosphorylation.