Salvage of the thiamin pyrimidine moiety by plant TenA proteins lacking an active-site cysteine

Abstract

The TenA protein family occurs in prokaryotes, plants and fungi; it has two subfamilies, one (TenA_C) having an active-site cysteine, the other (TenA_E) not. TenA_C proteins participate in thiamin salvage by hydrolysing the thiamin breakdown product amino-HMP (4-amino-5-aminomethyl-2-methylpyrimidine) to HMP (4-amino-5-hydroxymethyl-2-methylpyrimidine); the function of TenA_E proteins is unknown. Comparative analysis of prokaryote and plant genomes predicted that (i) TenA_E has a salvage role similar to, but not identical with, that of TenA_C and (ii) that TenA_E and TenA_C also have non-salvage roles since they occur in organisms that cannot make thiamin. Recombinant Arabidopsis and maize TenA_E proteins (At3g16990, GRMZM2G080501) hydrolysed amino-HMP to HMP and, far more actively, hydrolysed the N-formyl derivative of amino-HMP to amino-HMP. Ablating the At3g16990 gene in a line with a null mutation in the HMP biosynthesis gene ThiC prevented its rescue by amino-HMP. Ablating At3g16990 in the wild-type increased sensitivity to paraquat-induced oxidative stress; HMP overcame this increased sensitivity. Furthermore, the expression of TenA_E and ThiC genes in Arabidopsis and maize was inversely correlated. These results indicate that TenA_E proteins mediate amidohydrolase and aminohydrolase steps in the salvage of thiamin breakdown products. As such products can be toxic, TenA_E proteins may also pre-empt toxicity.

Does Abiotic Stress Cause Functional B Vitamin Deficiency in Plants?

“…The Arabidopsis gene specifying the thiazole salvage enzyme ThiM (Yazdani et al, 2013) is not upregulated (Fig. 5), which fits with the thiazole moiety of thiamin being more prone to irreversible damage than the pyrimidine moiety, and hence not as recyclable (Zallot et al, 2014).…”

“…Given the suicide nature of the THI4 enzyme, it is striking that THI4 was the most highly or second most highly induced gene in cotton (Gossypium hirsutum) seedlings exposed to cold, drought, salt, or high pH Gerdes et al (2012) except for the omission of compartmentation and the addition of two thiamin salvage reactions (Yazdani et al, 2013;Zallot et al, 2014). Circles are metabolites, arrows are reactions, and rectangles are enzymes.…”

“…TenA_E mediates two successive steps in the recovery of the pyrimidine moiety from thiamin damaged in the thiazole moiety (Zallot et al, 2014). The Arabidopsis gene encoding TenA_E is upregulated by several abiotic stresses, in common with thiamin synthesis genes ( Fig.…”

Arabidopsis TH2 Encodes the Orphan Enzyme Thiamin Monophosphate Phosphatase

“…Further analysis of single-copy k-mers from the surrounding region of the Est genome sequence (Schmitz et al, 2013) resolved a 13.9-kb deletion in th2-1 between nucleotides 12,075,450 and 12,089,360 of the chromosome 5 reference sequence. Notably, one of the four genes in this interval, At5g32470, encodes a protein that has previously been implicated in thiamin metabolism (Zallot et al, 2014); this protein, which is conserved throughout land plants, comprises an N-terminal TenA domain and a C-terminal HAD domain (Figure 2A). By contrast, the annotations of At5g32440, At5g32450, and At5g32460 ( Figure 2B) did not suggest obvious connections to thiamin.…”

Characterization of Thiamin Phosphate Kinase in the Hyperthermophilic Archaeon <i>Pyrobaculum calidifontis</i>

“…We recently reported that HET kinase (ThiM), another salvage enzyme, is also lacking in P. calidifontis (6). Since thiamin is chemically labile, especially in a high-temperature environment, and a pyrimidine moiety is generally more stable than a thiazole one (14), it seems likely that the salvage enzyme for only the HMP moiety derived from thiamin degradation has evolved in this hyperthermophilic archaeon.…”