Thiamine Biosynthesis in Escherichia coli: Identification of the Intermediate and By‐Product Derived from Tyrosine

Abstract

In anaerobic organisms such as E. coli the tyrosine lyase ThiH is essential for the biosynthesis of the thiazole moiety of the vitamin thiamine. ThiH is a member of the “radical AdoMet” family. The products formed by cleavage of tyrosine in vitro have been identified and suggest a radical‐mediated cleavage resulting in p‐cresol and dehydroglycine which is hydrolyzed to glyoxylate.

A glycyl free radical as the precursor in the synthesis of carbon monoxide and cyanide by the [FeFe]‐hydrogenase maturase HydG

“…Plausible mechanisms for CO and CN À synthesis by HydG from tyrosine may be postulated if their precursor is not DHG but the glycyl radical H 2 N-Å CH-CO À 2 . As has been discussed in the case of ThiH [20], H 2 N-Å CH-CO À 2 can be generated by the energetically favorable homolytic cleavage of the tyrosyl radical (Fig. 2), which in turn, is produced by H Å extraction from tyrosine by the 5 0 -deoxyadenosyl radical (DOA Å , the product of SAM cleavage).…”

“…The number of reconstituted [4Fe-4S] clusters was assessed by UV-visible (5) from the tyrosyl radical (1). In in vitro studies of HydG [11] and ThiH [20], the products of the reaction of tyrosine have been identified as p-cresol (4) [11,20] for the former and pcresol and glyoxylate (7) for the latter [20]. Glyoxylate is the hydrolytic product of dehydroglycine.…”

“…In 2007, we solved the crystal structure of HydE from Thermotoga maritima (Tm) and found that it binds SCN À very tightly [19]. Subsequently, we also showed that, like ThiH [20], HydG uses tyrosine to form p-cresol and either dehydroglycine (DHG) or the related glycyl radical (Fig. 2).…”

Characterization of NocL Involved in Thiopeptide Nocathiacin I Biosynthesis

“…Mutational Analysis of NocL-NocL and NosL both belong to the ThiH subfamily of radical AdoMet enzymes that cleave the C␣-C␤ bond of aromatic amino acids (26,36,37). Similar to other radical AdoMet proteins, this protein subfamily possesses a conserved CXXXCXXC motif for binding of the [4Fe-4S] cluster, a conserved "GE" motif proposed for binding of the methionine part of AdoMet, and a relatively conserved "GXLXG" motif for binding of the adenine part of AdoMet (Fig.…”

Metallocofactor assembly for [FeFe]-hydrogenases

“…Sequence analysis of HydG suggested a close relationship to a radical SAM enzyme, ThiH, which cleaves tyrosine to yield p-cresol and dehydroglycine [7,8]. Enzymes of the radical SAM superfamily share a common mechanism of radical reaction initiation, using a [4Fe-4S] + cluster to reductively cleave SAM, which yields methionine and the 5ʹ-deoxyadenosyl radical, a highly reactive primary radical [9] (Figure 1b).…”