Ishibashi Matsujiro, Arakawa Tsutomu, Philo John S, Sakashita Kentaro, Yonezawa Yasushi, Tokunaga Hiroko, Tokunaga Masao
Laboratory of Applied and Molecular Microbiology, Faculty of Agriculture, Kagoshima University, 1-21-24 Korimoto, Kagoshima 890-0065, Japan.
FEMS Microbiol Lett. 2002 Nov 5;216(2):235-41. doi: 10.1111/j.1574-6968.2002.tb11441.x.
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.
大多数来自极端嗜盐古菌的嗜盐酶在从高盐培养基转移到低盐培养基后会立即变性。然而，来自极端嗜盐古菌盐沼盐杆菌的核苷二磷酸激酶（HsNDK）似乎是个例外，因为该酶即使在低盐条件下也表现出催化活性。在这里，我们展示了HsNDK在高盐和低盐条件下均具有活性的机制，即高盐培养基中的HsNDK六聚体在低盐培养基中解离成二聚体而不会变性。观察到的亚基结构变化伴随着α-螺旋含量的大幅下降和热敏感性的降低，但仍保持构象。这种分别在高盐和低盐条件下从六聚体到二聚体的新型转变，似乎是HsNDK避免不可逆变性的机制。
