Structure of a halophilic nucleoside diphosphate kinase fromHalobacterium salinarum

Abstract
Nucleoside diphosphate kinase from the halophilic archaeon Halobacterium salinarum was crystallized in a free state and a substrate‐bound form with CDP. The structures were solved to a resolution of 2.35 and 2.2 Å, respectively. Crystals with the apo‐form were obtained with His6‐tagged enzyme, whereas the untagged form was used for co‐crystallization with the nucleotide. Crosslinking under different salt and pH conditions revealed a stronger oligomerization tendency for the tagged protein at low and high salt concentrations. The influence of the His6‐tag on the halophilic nature of the enzyme is discussed on the basis of the observed structural properties.