title: Compatible solute effects on thermostability of glutamine synthetase and aspartate transcarbamoylase from Methanococcus jannaschii.
abstract: Methanococcus jannaschii accumulates alpha- and beta-glutamate as osmolytes. The effect of these and other solutes on the thermostability of two multisubunit metabolic enzymes from M. jannaschii, aspartate transcarbamoylase catalytic trimer (ATCase C3) and glutamine synthetase (GS), has been measured and compared to solute effects on bacterial mesophilic counterparts in order to explore if osmolytes accumulated by each organism can preferentially stabilize the proteins to thermal unfolding. For both ATCase enzymes and for the B. subtilis GS, the solutes normally accumulated by the organism were very effective in protecting the enzyme from losing activity at high temperatures, although solute effects on loss of secondary structure did not necessarily correlate with this thermoprotection of activity. The recombinant M. jannaschii GS exhibited quite different behavior. The pure enzyme had a thermal unfolding transition with a midpoint temperature (Tm) less than 60 degrees C, well under the growth temperature of the organism (85 degrees C). None of the small molecule solutes tested (including the K+-glutamate isomers accumulated by M. jannaschii) significantly stabilized the protein to incubation at 85 degrees C. Instead, protein-protein interactions, as illustrated by E. coli GroEL or ribosomal protein L2 stabilization of GS, appeared to be the dominant factor in stabilizing this archaeal enzyme at the growth temperature.
authors.affiliation: Merkert Chemistry Center, Boston College, Chestnut Hill, MA 02467, USA.
authors.forename: Kelly
authors.initials: K
authors.lastname: Neelon
authors.forename: Harold J
authors.initials: HJ
authors.lastname: Schreier
authors.forename: Heather
authors.initials: H
authors.lastname: Meekins
authors.forename: Patrice M
authors.initials: PM
authors.lastname: Robinson
authors.forename: Mary F
authors.initials: MF
authors.lastname: Roberts
mesh_terms: D001221:Aspartate Carbamoyltransferase / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry*; D018834:Chaperonin 60 / Q000737:chemistry; D004795:Enzyme Stability; D004926:Escherichia coli / Q000201:enzymology; D005974:Glutamate-Ammonia Ligase / Q000737:chemistry*; D018698:Glutamic Acid / Q000737:chemistry; D006358:Hot Temperature; D017017:Methanococcus / Q000201:enzymology*; D011489:Protein Denaturation; D017510:Protein Folding; D012269:Ribosomal Proteins / Q000737:chemistry; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D018834:Chaperonin 60; D012269:Ribosomal Proteins; C029466:ribosomal protein L2; D018698:Glutamic Acid; D001221:Aspartate Carbamoyltransferase; D005974:Glutamate-Ammonia Ligase