Experimental characterization of two archaeal inosine 5'-monophosphate cyclohydrolases.

There is variability as to how archaea catalyze the final step of de novo purine biosynthesis to form inosine 5'-monophosphate (IMP) from 5-formamidoimidazole-4-carboxamide ribonucleotide (FAICAR). Although non-archaea almost uniformly use the bifunctional PurH protein, which has an N-terminal IMP cyclohydrolase (PurH2) fused to a C-terminal folate-dependent aminoimidazole-4-carboxamide ribonucleotide (AICAR) formyltransferase (PurH1) domain, a survey of the genomes of archaea reveals use of PurH2 (with or without fusion to PurH1), the "euryarchaeal signature protein" PurO, or an unidentified crenarchaeal IMP cyclohydrolase. In this report, we present the cloning and functional characterization of two representatives of the known IMP cyclohydrolase families.

Purine biosynthesis in archaea: variations on a theme.

Background: The ability to perform de novo biosynthesis of purines is present in organisms in all three domains of life, reflecting the essentiality of these molecules to life. Although the pathway is quite similar in eukaryotes and bacteria, the archaeal pathway is more variable. A careful manual curation of genes in this pathway demonstrates the value of manual curation in archaea, even in pathways that have been well-studied in other domains.

Investigations of the roles of arginine 115 and lysine 120 in the active site of 5,10-methenyltetrahydrofolate synthetase from Mycoplasma pneumoniae.

5,10-Methenyltetrahydrofolate synthetase (MTHFS) catalyzes the conversion of 5-formyltetrahydrofolate to 5,10-methenyltetrahydrofolate coupled to the hydrolysis of ATP. A co-crystal structure of MTHFS bound to its substrates has been published (Chen et al., Proteins 56:839-843, 2005) that provides insights into the mechanism of this reaction.