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Biochem J. 2014 Oct 1;463(1):145-55. doi: 10.1042/BJ20140522.

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

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*Microbiology and Cell Science Department, University of Florida, Gainesville, FL 32611, U.S.A.
†Department of Biochemistry and Molecular Biology, University of Nevada, Reno, NV 89557, U.S.A.
‡Department of Botany and Plant Pathology, Oregon State University, Hermiston, OR 97838, U.S.A.
§Horticultural Sciences Department, University of Florida, Gainesville, FL 32611, U.S.A.
∥Mathematics and Computer Science Division, Argonne National Laboratory, Argonne, IL 60439, U.S.A.
¶College of Medicine, University of Florida, Gainesville, FL 32610, U.S.A.
**Department of Biological Sciences and Northeast Structural Genomics Consortium, Columbia University, New York, NY 10027, U.S.A.


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.

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