title: Secondary and quaternary structural transition of the halophilic archaeon nucleoside diphosphate kinase under high- and low-salt conditions.
abstract: Most halophilic enzymes from extremely halophilic archaea are denatured immediately after transfer from high-salt to low-salt medium. However, nucleoside diphosphate kinase (HsNDK) from the extremely halophilic archaeon Halobacterium salinarum seems to be exceptional, since the enzyme exhibited catalytic activity even under the low-salt condition. Here we show the mechanism how HsNDK is active under both high- and low-salt conditions that the HsNDK hexamer in high-salt medium dissociates into a dimer in the low-salt medium without denaturation. The observed change of the subunit structure was accompanied by a large decrease of alpha-helical content and lowered thermal sensitivity, yet keeping the conformations. This novel hexamer to dimer conversion under high- and low-salt conditions, respectively, seems to be the mechanism by which HsNDK is avoided from the irreversible denaturation.
authors.affiliation: Laboratory of Applied and Molecular Microbiology, Faculty of Agriculture, Kagoshima University, 1-21-24 Korimoto, Kagoshima 890-0065, Japan.
authors.forename: Matsujiro
authors.initials: M
authors.lastname: Ishibashi
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Arakawa
authors.forename: John S
authors.initials: JS
authors.lastname: Philo
authors.forename: Kentaro
authors.initials: K
authors.lastname: Sakashita
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Yonezawa
authors.forename: Hiroko
authors.initials: H
authors.lastname: Tokunaga
authors.forename: Masao
authors.initials: M
authors.lastname: Tokunaga
mesh_terms: D002942:Circular Dichroism; D004789:Enzyme Activation / Q000187:drug effects; D004795:Enzyme Stability; D019617:Halobacterium salinarum / Q000737:chemistry / Q000201:enzymology*; D009701:Nucleoside-Diphosphate Kinase / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation / Q000187:drug effects*; D011489:Protein Denaturation; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D012965:Sodium Chloride / Q000494:pharmacology*; D013329:Structure-Activity Relationship; D013696:Temperature
chemical_list: D012965:Sodium Chloride; D009701:Nucleoside-Diphosphate Kinase