TenA-like proteins including TenA_C and TenA_E proteins, as well as pyrroloquinoline quinone (PQQ) synthesis protein C
TenA proteins participate in thiamin metabolism and can be classified into two classes: TenA_C which has an active site Cys, and TenA_E which does not; TenA_E proteins often have a pair of structurally conserved Glu residues in the active site. TenA_C proteins (EC 3.5.99.2) catalyze the hydrolysis of the thiamin breakdown product amino-HMP (4-amino-5-amino-methyl-2-methylpyrimidine) to 4-amino-5-hydroxymethyl-2-methylpyrimidine (HMP) in a thiamin salvage pathway; the role of TenA_E proteins is less clear. Arabidopsis thaliana TenA_E hydrolyzes amino-HMP to AMP, and the N-formyl derivative of amino-HMP to amino-HMP, but does not hydrolyze thiamin. Bacillus subtilis TenA_C can hydrolyze amino-HMP to AMP and can catalyze the hydrolysis of thiamin. Saccharomyces cerevisiae THI20 includes a C-terminal tetrameric TenA-like domain fused to an N-terminal ThiD domain, and participates in thiamin biosynthesis, degradation and salvage; the TenA-like domain catalyzes the production of HMP from thiamin degradation products (salvage). Bacillus halodurans TenA_C participates in a salvage pathway where the thiamine degradation product 2-methyl-4-formylamino-5-aminomethylpyrimidine (formylamino-HMP) is hydrolyzed first to amino-HMP by the YlmB protein, and the amino-HMP is then hydrolyzed by TenA to produce HMP. Helicobacter pylori TenA_C is also thought to catalyze a salvage reaction but the pyrimidine substrate has not yet been identified. It has also been suggested that TenA proteins act as transcriptional regulators based on changes in gene-expression patterns when TenA is overexpressed in Bacillus subtilis, however this effect may be indirect; Pyrococcus furiosus TenA_E lacks appropriate surface charges for DNA interactions. This family also includes bacterial coenzyme pyrroloquinoline quinone (PQQ) synthesis protein C (PQQC), an oxidase involved in the final step of PQQ biosynthesis, and CADD, a Chlamydia protein that interacts with death receptors.
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