One of the hallmarks of halophilic properties is reversibility of thermal unfolding. A nucleoside diphosphate
kinase (NDK) from a moderate halophile Halomonas sp. 593 (HaNDK) follows this behavior. His-tagged chimeric NDK
(HisPaHaNDK) consisting of an N-terminal half of a non-halophilic Pseuodomonas aeruginosa NDK (PaNDK) and a Cterminal
half of HaNDK loses this reversible property, indicating a critical role of the N-terminal portion of PaNDK in determining
the reversibility of the chimeric protein. Various mutations were introduced at Arg45 and Lys61, based on the
model NDK structure. It appears that having Glu at position 45 is critical in conferring the thermal reversibility to HisPa-
HaNDK chimeric protein.
Keywords: Acidic amino acid, halophilic, heat-denaturation, nucleoside diphosphate kinase, refolding, reversibility.
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