TauD

TauD stands for taurine dioxygenase, a non-heme iron(II)/α-ketoglutarate-dependent dioxygenase found in bacteria that metabolize taurine. In the taurine utilization pathway, TauD catalyzes the oxidative cleavage of taurine to aminoacetaldehyde and sulfite, using molecular oxygen and 2-oxoglutarate as cosubstrates; the decarboxylation of 2-OG yields succinate and CO2. The overall reaction is taurine plus 2-oxoglutarate and O2 producing aminoacetaldehyde, sulfite, succinate, and CO2.

Mechanistically, TauD belongs to the family of non-heme iron(II)/α-ketoglutarate dioxygenases and features a conserved iron center coordinated by a facial triad, typically two histidines and an aspartate. 2-oxoglutarate binds to the iron as a cosubstrate, and upon O2 activation an iron-oxo intermediate forms that facilitates substrate oxidation and subsequent cleavage of the C–S bond in taurine. This leads to release of sulfite and the aldehyde product, aminoacetaldehyde, with 2-OG being decarboxylated to succinate and CO2.

Structure and genetics-wise, TauD is usually a cytosolic enzyme of roughly 30–40 kilodaltons and is encoded by the tauD gene, often located in an operon with tauABC, which encode taurine transport and related components. In bacteria such as Escherichia coli and Pseudomonas species, TauD has been studied extensively, and multiple crystal structures have illuminated active-site geometry, substrate positioning, and cofactor interactions.

Significance-wise, TauD is a model enzyme for the class of nonheme Fe(II)/αKG dioxygenases, illustrating how O2 activation and oxidative C–S bond cleavage are achieved in this enzyme family. Insights from TauD have informed broader understanding of sulfur metabolism and the mechanistic diversity of Fe/2OG-dependent enzymes.