Structural determination of functional units of the nucleotide binding domain (NBD94) of the reticulocyte binding protein Py235 of Plasmodium yoelii.

Invasion of the red blood cells (RBC) by the merozoite of malaria parasites involves a large number of receptor ligand interactions. The reticulocyte binding protein homologue family (RH) plays an important role in erythrocyte recognition as well as virulence. Recently, it has been shown that members of RH in addition to receptor binding may also have a role as ATP/ADP sensor. A 94 kDa region named Nucleotide-Binding Domain 94 (NBD94) of Plasmodium yoelii YM, representative of the putative nucleotide binding region of RH, has been demonstrated to bind ATP and ADP selectively. Binding of ATP or ADP induced nucleotide-dependent structural changes in the C-terminal hinge-region of NBD94, and directly impacted on the RBC binding ability of RH.In order to find the smallest structural unit, able to bind nucleotides, and its coupling module, the hinge region, three truncated domains of NBD94 have been generated, termed NBD94(444-547), NBD94(566-663) and NBD94(674-793), respectively. Using fluorescence correlation spectroscopy NBD94(444-547) has been identified to form the smallest nucleotide binding segment, sensitive for ATP and ADP, which became inhibited by 4-Chloro-7-nitrobenzofurazan. The shape of NBD94(444-547) in solution was calculated from small-angle X-ray scattering data, revealing an elongated molecule, comprised of two globular domains, connected by a spiral segment of about 73.1 A in length. The high quality of the constructs, forming the hinge-region, NBD94(566-663) and NBD94(674-793) enabled to determine the first crystallographic and solution structure, respectively. The crystal structure of NBD94(566-663) consists of two helices with 97.8 A and 48.6 A in length, linked by a loop. By comparison, the low resolution structure of NBD94(674-793) in solution represents a chair-like shape with three architectural segments.These structures give the first insight into how nucleotide binding impacts on the overall structure of RH and demonstrates the potential use of this region as a novel drug target

Crystallization and preliminary X-ray diffraction analysis of the wild-type haloalkane dehalogenase DhaA and its variant DhaA13 complexed with different ligands.

Haloalkane dehalogenases make up an important class of hydrolytic enzymes which catalyse the cleavage of carbon-halogen bonds in halogenated aliphatic compounds. There is growing interest in these enzymes owing to their potential use in environmental and industrial applications. The haloalkane dehalogenase DhaA from Rhodococcus rhodochrous NCIMB 13064 can slowly detoxify the industrial pollutant 1,2,3-trichloropropane (TCP). Structural analysis of this enzyme complexed with target ligands was conducted in order to obtain detailed information about the structural limitations of its catalytic properties. In this study, the crystallization and preliminary X-ray analysis of complexes of wild-type DhaA with 2-propanol and with TCP and of complexes of the catalytically inactive variant DhaA13 with the dye coumarin and with TCP are described. The crystals of wild-type DhaA were plate-shaped and belonged to the triclinic space group P1, while the variant DhaA13 can form prism-shaped crystals belonging to the orthorhombic space group P2(1)2(1)2(1) as well as plate-shaped crystals belonging to the triclinic space group P1. Diffraction data for crystals of wild-type DhaA grown from crystallization solutions with different concentrations of 2-propanol were collected to 1.70 and 1.26 Å resolution, respectively. A prism-shaped crystal of DhaA13 complexed with TCP and a plate-shaped crystal of the same variant complexed with the dye coumarin diffracted X-rays to 1.60 and 1.33 Å resolution, respectively. A crystal of wild-type DhaA and a plate-shaped crystal of DhaA13, both complexed with TCP, diffracted to atomic resolutions of 1.04 and 0.97 Å, respectively