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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.

Author information

1
*Microbiology and Cell Science Department, University of Florida, Gainesville, FL 32611, U.S.A.
2
†Department of Biochemistry and Molecular Biology, University of Nevada, Reno, NV 89557, U.S.A.
3
‡Department of Botany and Plant Pathology, Oregon State University, Hermiston, OR 97838, U.S.A.
4
§Horticultural Sciences Department, University of Florida, Gainesville, FL 32611, U.S.A.
5
∥Mathematics and Computer Science Division, Argonne National Laboratory, Argonne, IL 60439, U.S.A.
6
¶College of Medicine, University of Florida, Gainesville, FL 32610, U.S.A.
7
**Department of Biological Sciences and Northeast Structural Genomics Consortium, Columbia University, New York, NY 10027, U.S.A.

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.

PMID:
25014715
DOI:
10.1042/BJ20140522
[Indexed for MEDLINE]
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