Involvement of thiaminase II encoded by theTHI20gene in thiamin salvage ofSaccharomyces cerevisiae

Abstract

The physiological significance of thiaminase II, which catalyzes the hydrolysis of thiamin, has remained elusive for several decades. The C-terminal domains of THI20 family proteins (THI20/21/22) and the whole region of PET18 gene product of Saccharomyces cerevisiae are homologous to bacterial thiaminase II. On the other hand, the N-terminal domains of THI20 and THI21 encode 2-methyl-4-amino-5-hydroxymethylpyrimidine kinase and 2-methyl-4-amino-5-hydroxymethylpyrimidine phosphate kinase involved in the thiamin synthetic pathway. In this study, it was first indicated that the C-terminal domains of the THI20 family and PET18 are not required for de novo thiamin synthesis in S. cerevisiae, using a quadruple deletion strain expressing the N-terminal domain of THI20. Biochemical analysis using cell-free extracts and recombinant proteins demonstrated that yeast thiaminase II activity is exclusively encoded by THI20. It appeared that Thi20p has an affinity for the pyrimidine moiety of thiamin, and HMP produced by the thiaminase II activity is immediately phosphorylated. Thi20p was found to participate in the formation of thiamin from two synthetic antagonists, pyrithiamin and oxythiamin, by hydrolyzing both antagonists and phosphorylating HMP to give HMP pyrophosphate. Furthermore, 2-methyl-4-amino-5-aminomethylpyrimidine, a presumed naturally occurring thiamin precursor, was effectively converted to HMP by incubation with Thi20p. It is proposed that the thiaminase II activity of Thi20p is involved in the thiamin salvage pathway by catalyzing the hydrolysis of HMP precursors in S. cerevisiae.

Green Evolution and Dynamic Adaptations Revealed by Genomes of the Marine Picoeukaryotes Micromonas

“…Other options appeared available for use of precursors derived from thiamine degradation products, at least in CCMP1545 and Ostreococcus. For these Mameillales, TENA/THI4 superfamily members had highest identity (apart from to each other) to bacterial TENA genes involved in thiamine salvage in bacteria (150) and yeast (151).…”

A Rapid Method for Assaying Thiaminase I Activity in Diverse Biological Samples

“…Thiaminase I catalyzes the replacement of the thiazole moiety of thiamine with any of a variety of organic nucleophiles [10], [11]. Thiaminase II degrades thiamine using a similar mechanism, except water serves as the nucleophile [12], [13]. Thiaminase I is the only thiaminase linked to fish reproductive failure and animal mortality, consequently it has been the focus of studies investigating syndromes associated with enzymatic thiamine degradation [14], [15], [16].…”

Arabidopsis TH2 Encodes the Orphan Enzyme Thiamin Monophosphate Phosphatase

“…TenA_C proteins from yeast (Onozuka et al, 2008) and bacteria (Jenkins et al, 2007;Barison et al, 2009) participate in salvage of the thiamin pyrimidine moiety; they hydrolyze the breakdown product 4-amino-5-aminomethyl-2-methylpyrimidine (amino-HMP) to the thiamin precursor 4-amino-5-hydroxymethyl-2-methylpyrimidine (HMP) ( Figure 5A) and can in some cases also slowly hydrolyze thiamin itself. TenA_C proteins lack activity against the N-formyl derivative of amino-HMP (another thiamin breakdown product; Figure 5A) (Jenkins et al, 2007;Zallot et al, 2014).…”