title: Zinc-independent folate biosynthesis: genetic, biochemical, and structural investigations reveal new metal dependence for GTP cyclohydrolase IB.
abstract: GTP cyclohydrolase I (GCYH-I) is an essential Zn(2+)-dependent enzyme that catalyzes the first step of the de novo folate biosynthetic pathway in bacteria and plants, the 7-deazapurine biosynthetic pathway in Bacteria and Archaea, and the biopterin pathway in mammals. We recently reported the discovery of a new prokaryotic-specific GCYH-I (GCYH-IB) that displays no sequence identity to the canonical enzyme and is present in approximately 25% of bacteria, the majority of which lack the canonical GCYH-I (renamed GCYH-IA). Genomic and genetic analyses indicate that in those organisms possessing both enzymes, e.g., Bacillus subtilis, GCYH-IA and -IB are functionally redundant, but differentially expressed. Whereas GCYH-IA is constitutively expressed, GCYH-IB is expressed only under Zn(2+)-limiting conditions. These observations are consistent with the hypothesis that GCYH-IB functions to allow folate biosynthesis during Zn(2+) starvation. Here, we present biochemical and structural data showing that bacterial GCYH-IB, like GCYH-IA, belongs to the tunneling-fold (T-fold) superfamily. However, the GCYH-IA and -IB enzymes exhibit significant differences in global structure and active-site architecture. While GCYH-IA is a unimodular, homodecameric, Zn(2+)-dependent enzyme, GCYH-IB is a bimodular, homotetrameric enzyme activated by a variety of divalent cations. The structure of GCYH-IB and the broad metal dependence exhibited by this enzyme further underscore the mechanistic plasticity that is emerging for the T-fold superfamily. Notably, while humans possess the canonical GCYH-IA enzyme, many clinically important human pathogens possess only the GCYH-IB enzyme, suggesting that this enzyme is a potential new molecular target for antibacterial development.
authors.affiliation: Berkeley Center for Structural Biology, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA.
authors.forename: Banumathi
authors.initials: B
authors.lastname: Sankaran
authors.forename: Shilah A
authors.initials: SA
authors.lastname: Bonnett
authors.forename: Kinjal
authors.initials: K
authors.lastname: Shah
authors.forename: Scott
authors.initials: S
authors.lastname: Gabriel
authors.forename: Robert
authors.initials: R
authors.lastname: Reddy
authors.forename: Paul
authors.initials: P
authors.lastname: Schimmel
authors.forename: Dmitry A
authors.initials: DA
authors.lastname: Rodionov
authors.forename: Valérie
authors.initials: V
authors.lastname: de Crécy-Lagard
authors.forename: John D
authors.initials: JD
authors.lastname: Helmann
authors.forename: Dirk
authors.initials: D
authors.lastname: Iwata-Reuyl
authors.forename: Manal A
authors.initials: MA
authors.lastname: Swairjo
mesh_terms: D000595:Amino Acid Sequence; D001412:Bacillus subtilis / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D019295:Computational Biology; D018360:Crystallography, X-Ray; D005492:Folic Acid / Q000096:biosynthesis*; D006136:GTP Cyclohydrolase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009344:Neisseria gonorrhoeae / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017386:Sequence Homology, Amino Acid; D015032:Zinc / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D008345:Manganese; D005492:Folic Acid; D006136:GTP Cyclohydrolase; D015032:Zinc