Guanosine triphosphate-8-formylhydrolase

QueE: A Radical SAM Enzyme Involved in the Biosynthesis of 7-Deazapurine Containing Natural Products

7-Carboxy-7-deazaguanine (CDG) is a common intermediate in the biosynthesis of 7-deazapurine-containing natural products. The biosynthesis of CDG from GTP requires three enzymes: GTP cyclohydrolase I, 6-carboxy-5,6,7,8-tetrahydropterin (CPH4) synthase, and CDG synthase (QueE). QueE is a member of the radical S-adenosyl-l-methionine (SAM) superfamily and catalyzes the SAM-dependent radical-mediated ring contraction of CPH4 to generate CDG. This chapter focuses on methods to reconstitute the activity of QueE in vitro.

Biosynthesis of pyrrolopyrimidines

Pyrrolopyrimidine containing compounds, also known as 7-deazapurines, are a collection of purine-based metabolites that have been isolated from a variety of biological sources and have diverse functions which range from secondary metabolism to RNA modification. To date, nearly 35 compounds with the common 7-deazapurine core structure have been described. This article will illustrate the structural diversity of these compounds and review the current state of knowledge on the biosynthetic pathways that give rise to them.

Deciphering deazapurine biosynthesis: pathway for pyrrolopyrimidine nucleosides toyocamycin and sangivamycin

Pyrrolopyrimidine nucleosides analogs, collectively referred to as deazapurines, are an important class of structurally diverse compounds found in a wide variety of biological niches. In this report, a cluster of genes from Streptomyces rimosus (ATCC 14673) involved in production of the deazapurine antibiotics sangivamycin and toyocamycin was identified. The cluster includes toyocamycin nitrile hydratase, an enzyme that catalyzes the conversion of toyocamycin to sangivamycin. In addition to this rare nitrile hydratase, the cluster encodes a GTP cyclohydrolase I, linking the biosynthesis of deazapurines to folate biosynthesis, and a set of purine salvage/biosynthesis genes, which presumably convert the guanine moiety from GTP to the adenine-like deazapurine base found in toyocamycin and sangivamycin. The gene cluster presented here could potentially serve as a model to allow identification of deazapurine biosynthetic pathways in other bacterial species.

Biosynthesis of 7-deazaguanosine-modified tRNA nucleosides: a new role for GTP cyclohydrolase I

Queuosine (Q) and archaeosine (G(+)) are hypermodified ribonucleosides found in tRNA. Q is present in the anticodon region of tRNA(GUN) in Eukarya and Bacteria, while G(+) is found at position 15 in the D-loop of archaeal tRNA. Prokaryotes produce these 7-deazaguanosine derivatives de novo from GTP through the 7-cyano-7-deazaguanine (pre-Q(0)) intermediate, but mammals import the free base, queuine, obtained from the diet or the intestinal flora. By combining the results of comparative genomic analysis with those of genetic studies, we show that the first enzyme of the folate pathway, GTP cyclohydrolase I (GCYH-I), encoded in Escherichia coli by folE, is also the first enzyme of pre-Q(0) biosynthesis in both prokaryotic kingdoms. Indeed, tRNA extracted from an E. coli DeltafolE strain is devoid of Q and the deficiency is complemented by expressing GCYH-I-encoding genes from different bacterial or archaeal origins. In a similar fashion, tRNA extracted from a Haloferax volcanii strain carrying a deletion of the GCYH-I-encoding gene contains only traces of G(+). These results link the production of a tRNA-modified base to primary metabolism and further clarify the biosynthetic pathway for these complex modified nucleosides.