title: Conserved active site cysteine residue of archaeal THI4 homolog is essential for thiamine biosynthesis in Haloferax volcanii.
abstract: BACKGROUND
  Thiamine (vitamin B1) is synthesized de novo by certain yeast, fungi, plants, protozoans, bacteria and archaea. The pathway of thiamine biosynthesis by archaea is poorly understood, particularly the route of sulfur relay to form the thiazole ring. Archaea harbor structural homologs of both the bacterial (ThiS-ThiF) and eukaryotic (THI4) proteins that mobilize sulfur to thiazole ring precursors by distinct mechanisms.
  
  
  RESULTS
  Based on comparative genome analysis, halophilic archaea are predicted to synthesize the pyrimidine moiety of thiamine by the bacterial pathway, initially suggesting that also a bacterial ThiS-ThiF type mechanism for synthesis of the thiazole ring is used in which the sulfur carrier ThiS is first activated by ThiF-catalyzed adenylation. The only ThiF homolog of Haloferax volcanii (UbaA) was deleted but this had no effect on growth in the absence of thiamine. Usage of the eukaryotic THI4-type sulfur relay was initially considered less likely for thiamine biosynthesis in archaea, since the active-site cysteine residue of yeast THI4p that donates the sulfur to the thiazole ring by a suicide mechanism is replaced by a histidine residue in many archaeal THI4 homologs and these are described as D-ribose-1,5-bisphosphate isomerases. The THI4 homolog of the halophilic archaea, including Hfx. volcanii (HVO_0665, HvThi4) was found to differ from that of methanogens and thermococci by having a cysteine residue (Cys165) corresponding to the conserved active site cysteine of yeast THI4p (Cys205). Deletion of HVO_0665 generated a thiamine auxotroph that was trans-complemented by a wild-type copy of HVO_0665, but not the modified gene encoding an HvThi4 C165A variant.
  
  
  CONCLUSIONS
  Based on our results, we conclude that the archaeon Hfx. volcanii uses a yeast THI4-type mechanism for sulfur relay to form the thiazole ring of thiamine. We extend this finding to a relatively large group of archaea, including haloarchaea, ammonium oxidizing archaea, and some methanogen and Pyrococcus species, by observing that these organisms code for THI4 homologs that have a conserved active site cysteine residue which is likely used in thiamine biosynthesis. Thus, archaeal members of IPR002922 THI4 family that have a conserved cysteine active site should be reexamined for a function in thiamine biosynthesis.
authors.affiliation: Department of Microbiology and Cell Science, University of Florida, Gainesville, FL, 32611-0700, USA. sungminhwang@ufl.edu.
authors.forename: Sungmin
authors.initials: S
authors.lastname: Hwang
authors.affiliation: Department of Microbiology and Cell Science, University of Florida, Gainesville, FL, 32611-0700, USA. bcordova@ufl.edu.
authors.forename: Bryan
authors.initials: B
authors.lastname: Cordova
authors.affiliation: Department of Microbiology and Cell Science, University of Florida, Gainesville, FL, 32611-0700, USA. drapus@ufl.edu.
authors.forename: Nikita
authors.initials: N
authors.lastname: Chavarria
authors.affiliation: Department of Microbiology and Cell Science, University of Florida, Gainesville, FL, 32611-0700, USA. elbannad@gmail.com.
authors.forename: Dina
authors.initials: D
authors.lastname: Elbanna
authors.affiliation: Department of Microbiology and Cell Science, University of Florida, Gainesville, FL, 32611-0700, USA. stepmchugh@ufl.edu.
authors.forename: Stephen
authors.initials: S
authors.lastname: McHugh
authors.affiliation: Department of Microbiology and Cell Science, University of Florida, Gainesville, FL, 32611-0700, USA. jrojas24@ufl.edu.
authors.forename: Jenny
authors.initials: J
authors.lastname: Rojas
authors.affiliation: Department of Membrane Biochemistry, Max Planck Institute of Biochemistry, Am Klopferspitz 18, D-82152, Martinsried, Germany. fpf@biochem.mpg.de.
authors.forename: Friedhelm
authors.initials: F
authors.lastname: Pfeiffer
authors.affiliation: Department of Microbiology and Cell Science, University of Florida, Gainesville, FL, 32611-0700, USA. jmaupin@ufl.edu.|Genetics Institute, University of Florida, Gainesville, FL, 32611-0700, USA. jmaupin@ufl.edu.
authors.forename: Julie A
authors.initials: JA
authors.lastname: Maupin-Furlow
mesh_terms: D019843:Archaeal Proteins / Q000235:genetics / Q000378:metabolism*; D053898:Biosynthetic Pathways / Q000235:genetics; D020134:Catalytic Domain; D003545:Cysteine / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D005816:Genetic Complementation Test; D019622:Haloferax volcanii / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D013831:Thiamine / Q000096:biosynthesis*
chemical_list: D019843:Archaeal Proteins; D003545:Cysteine; D013831:Thiamine