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Site-specific Xer recombination plays a pivotal role in reshuffling genetic information. Here, we report the 2.5 Å crystal structure of XerA from the archaean Thermoplasma acidophilum. Crystallographic data reveal a uniquely open conformational state, resulting in a C-shaped clamp with an angle of ~ 48° and a distance of 57 Å between the core-binding and the catalytic domains. The catalytic nucleophile, Tyr264, is positioned in cis-cleavage mode by XerA's C-term tail that interacts with the CAT domain of a neighboring monomer without DNA substrate. Structural comparisons of tyrosine recombinases elucidate the dynamics of Xer recombinase. [ABSTRACT FROM AUTHOR]

Highlights: [•] Crystal structures of the apo and substrate-bound forms of hArgRS are described. [•] Similar interactions are formed upon binding to l-canavanine or l-arginine. [•] The interaction between Tyr312 and the oxygen of the oxyguanidino group differs. [•] Substrate-bound hArgRS has a tRNAArg acceptor arm cavity and a closed active site. [•] Newly identified regions in the N- and C-terminal domains of hArgRS are described. [ABSTRACT FROM AUTHOR]

Abstract: Creatine kinase is a member of the phosphagen kinase family, which catalyzes the reversible phosphoryl transfer reaction that occurs between ATP and creatine to produce ADP and phosphocreatine. Here, three structural aspects of human-brain-type-creatine-kinase (hBB-CK) were identified by X-ray crystallography: the ligand-free-form at 2.2Å; the ADP–Mg2+, nitrate, and creatine complex (transition-state-analogue complex; TSAC); and the ADP–Mg2+-complex at 2.0Å. The structures of ligand-bound hBB-CK revealed two different monomeric states in a single homodimer. One monomer is a closed form, either bound to TSAC or the ADP–Mg2+-complex, and the second monomer is an unliganded open form. These structural studies provide a detailed mechanism indicating that the binding of ADP–Mg2+ alone may trigger conformational changes in hBB-CK that were not observed with muscle-type-CK. [Copyright &y& Elsevier]