IMP cyclohydrolases in the domain Archaea

Abstract

There is some diversity as to how archaea effect the final step of de novo purine biosynthesis to form inosine 5′‐monophosphate (IMP) from 5‐formamidoimidazole‐4‐carboxamide ribonucleotide (FAICAR). A survey of the genomes of archaea reveals a mixture of PurH2 (with or without fusion to PurH1), the Euryarchaeal signature protein PurO, and an unidentified Crenarchaeal IMP cyclohydrolase. In this report, we present the cloning and functional characterization of three representatives of the known IMP cyclohydrolases. The locus TK0430 in Thermococcus kodakarensis encodes a PurO‐type IMP cyclohydrolase with demonstrated activity despite its position in a cluster of apparently redundant biosynthetic genes. The locus AF1811 from Archaeoglobus fulgidus encodes a PurH2‐type IMP cyclohydrolase that occurs in active form without fusion to a PurH1 protein. The locus HVO_0011 in Haloferax volcanii encodes a PurO‐type IMP cyclohydrolase active only at high salt concentrations. All three enzymes convert FAICAR to IMP in vitro, and two restore the growth on purine deficient media of an E. coli purine auxotroph lacking purH2.