title: Structure and function of a regulated archaeal triosephosphate isomerase adapted to high temperature.
abstract: Triosephophate isomerase (TIM) is a dimeric enzyme in eucarya, bacteria and mesophilic archaea. In hyperthermophilic archaea, however, TIM exists as a tetramer composed of monomers that are about 10% shorter than other eucaryal and bacterial TIM monomers. We report here the crystal structure of TIM from Thermoproteus tenax, a hyperthermophilic archaeon that has an optimum growth temperature of 86 degrees C. The structure was determined from both a hexagonal and an orthorhombic crystal form to resolutions of 2.5A and 2.3A, and refined to R-factors of 19.7% and 21.5%, respectively. In both crystal forms, T.tenax TIM exists as a tetramer of the familiar (betaalpha)(8)-barrel. In solution, however, and unlike other hyperthermophilic TIMs, the T.tenax enzyme exhibits an equilibrium between inactive dimers and active tetramers, which is shifted to the tetramer state through a specific interaction with glycerol-1-phosphate dehydrogenase of T.tenax. This observation is interpreted in physiological terms as a need to reduce the build-up of thermolabile metabolic intermediates that would be susceptible to destruction by heat. A detailed structural comparison with TIMs from organisms with growth optima ranging from 15 degrees C to 100 degrees C emphasizes the importance in hyperthermophilic proteins of the specific location of ionic interactions for thermal stability rather than their numbers, and shows a clear correlation between the reduction of heat-labile, surface-exposed Asn and Gln residues with thermoadaptation. The comparison confirms the increase in charged surface-exposed residues at the expense of polar residues.
authors.affiliation: Centre for Biomolecular Sciences, University of St Andrews, St Andrews, Fife KY16 9ST, Scotland, UK.
authors.forename: Helen
authors.initials: H
authors.lastname: Walden
authors.forename: Garry L
authors.initials: GL
authors.lastname: Taylor
authors.forename: Esben
authors.initials: E
authors.lastname: Lorentzen
authors.forename: Ehmke
authors.initials: E
authors.lastname: Pohl
authors.forename: Hauke
authors.initials: H
authors.lastname: Lilie
authors.forename: Alexander
authors.initials: A
authors.lastname: Schramm
authors.forename: Thomas
authors.initials: T
authors.lastname: Knura
authors.forename: Kim
authors.initials: K
authors.lastname: Stubbe
authors.forename: Britta
authors.initials: B
authors.lastname: Tjaden
authors.forename: Reinhard
authors.initials: R
authors.lastname: Hensel
mesh_terms: D000222:Adaptation, Physiological; D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D018360:Crystallography, X-Ray; D019641:DNA, Archaeal / Q000235:genetics; D019281:Dimerization; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020836:Protein Structure, Quaternary; D019711:Pyrococcus / Q000201:enzymology / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity; D013696:Temperature; D041542:Thermoproteus / Q000201:enzymology / Q000235:genetics; D014305:Triose-Phosphate Isomerase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D019843:Archaeal Proteins; D019641:DNA, Archaeal; D011994:Recombinant Proteins; D014305:Triose-Phosphate Isomerase