Crystallographic insights into a cobalt (III) sepulchrate based alternative cofactor system of P450 BM3 monooxygenase.

P450 BM3 is a multi-domain heme-containing soluble bacterial monooxygenase. P450 BM3 and variants are known to oxidize structurally diverse substrates. Crystal structures of individual domains of P450 BM3 are available. However, the spatial organization of the full-length protein is unknown. In this study, crystal structures of the P450 BM3 M7 heme domain variant with and without cobalt (III) sepulchrate are reported. Cobalt (III) sepulchrate acts as an electron shuttle in an alternative cofactor system employing zinc dust as the electron source. The crystal structure shows a binding site for the mediator cobalt (III) sepulchrate at the entrance of the substrate access channel. The mediator occupies an unusual position which is far from the active site and distinct from the binding of the natural redox partner (FAD/NADPH binding domain).

Structure-based Epitope Mapping of Mycobacterium tuberculosis Secretary Antigen MTC28.

Secretary proteins of Mycobacterium tuberculosis are key players of the mycobacterial infection pathway. MTC28 is a 28-kDa proline-rich secretary antigen of Mycobacterium tuberculosis and is only conserved in pathogenic strains of mycobacteria. Here we report the crystal structure of MTC28 at 2.8- and 2.15-Å resolutions for the structure-based epitope design. MTC28 shares a "mog1p"-fold consisting of seven antiparallel ß strands stacked between α helices. Five probable epitopes have been located on a solvent-accessible flexible region by computational analysis of the structure of MTC28. Simultaneously, the protein is digested with trypsin and the resulting fragments are purified by HPLC. Such 10 purified peptide fragments are screened against sera from patients infected with pulmonary tuberculosis (PTB). Two of these 10 fragments, namely (127)ALDITLPMPPR(137) and (138)WTQVPDPNVPDAFVVIADR(156),are found to be major immunogenic epitopes that are localized on the outer surface of the protein molecule and are part of a single continuous epitope that have been predicted in silico Mutagenesis and antibody inhibition studies are in accordance with the results obtained from epitope mapping.

Structural model of the cytosolic domain of the plant ethylene receptor 1 (ETR1).

Ethylene initiates important aspects of plant growth and development through disulfide-linked receptor dimers located in the endoplasmic reticulum. The receptors feature a small transmembrane, ethylene binding domain followed by a large cytosolic domain, which serves as a scaffold for the assembly of large molecular weight complexes of different ethylene receptors and other cellular participants of the ethylene signaling pathway. Here we report the crystallographic structures of the ethylene receptor 1 (ETR1) catalytic ATP-binding and the ethylene response sensor 1 dimerization histidine phosphotransfer (DHp) domains and the solution structure of the entire cytosolic domain of ETR1, all from Arabidopsis thaliana. The isolated dimeric ethylene response sensor 1 DHp domain is asymmetric, the result of different helical bending angles close to the conserved His residue. The structures of the catalytic ATP-binding, DHp, and receiver domains of ethylene receptors and of a homologous, but dissimilar, GAF domain were refined against experimental small angle x-ray scattering data, leading to a structural model of the entire cytosolic domain of the ethylene receptor 1. The model illustrates that the cytosolic domain is shaped like a dumbbell and that the receiver domain is flexible and assumes a position different from those observed in prokaryotic histidine kinases. Furthermore the cytosolic domain of ETR1 plays a key role, interacting with all other receptors and several participants of the ethylene signaling pathway. Our model, therefore, provides the first step toward a detailed understanding of the molecular mechanics of this important signal transduction process in plants.

A Crystallin Fold in the Interleukin-4-inducing Principle of Schistosoma mansoni Eggs (IPSE/α-1) Mediates IgE Binding for Antigen-independent Basophil Activation.

The IL-4-inducing principle from Schistosoma mansoni eggs (IPSE/α-1), the major secretory product of eggs from the parasitic worm S. mansoni, efficiently triggers basophils to release the immunomodulatory key cytokine interleukin-4. Activation by IPSE/α-1 requires the presence of IgE on the basophils, but the detailed molecular mechanism underlying activation is unknown. NMR and crystallographic analysis of IPSEΔNLS, a monomeric IPSE/α-1 mutant, revealed that IPSE/α-1 is a new member of the ßγ-crystallin superfamily. We demonstrate that this molecule is a general immunoglobulin-binding factor with highest affinity for IgE. NMR binding studies of IPSEΔNLS with the 180-kDa molecule IgE identified a large positively charged binding surface that includes a flexible loop, which is unique to the IPSE/α-1 crystallin fold. Mutational analysis of amino acids in the binding interface showed that residues contributing to IgE binding are important for IgE-dependent activation of basophils. As IPSE/α-1 is unable to cross-link IgE, we propose that this molecule, by taking advantage of its unique IgE-binding crystallin fold, activates basophils by a novel, cross-linking-independent mechanism.

Crystallographic identification of an unexpected protein complex in silkworm haemolymph.

The first crystal structure of a complex formed by two storage proteins, SP2 and SP3, isolated from their natural source, mulberry silkworm (Bombyx mori L.) haemolymph, has been determined. The structure was solved by molecular replacement using arylphorin, a protein rich in aromatic amino-acid residues, from oak silkworm as the initial model. The quality of the electron-density maps obtained from the X-ray diffraction experiment allowed the authors to detect that the investigated crystal structure was composed of two different arylphorins: SP2 and SP3. This discovery was confirmed by N-terminal sequencing. SP2 has been extensively studied previously, whereas only a few reports on SP3 are available. However, to date no structural studies have been reported for these proteins. These studies revealed that SP2 and SP3 exist in the silkworm body as a heterohexamer formed by one SP2 trimer and one SP3 trimer. The overall fold, consisting of three haemocyanin-like subdomains, of SP2 and SP3 is similar. Both proteins contain a conserved N-glycosylation motif in their structures.

Cloning, expression, purification and preliminary X-ray analysis of the dimerization domain of ethylene response sensor 1 (ERS1) from Arabidopsis thaliana.

Ethylene signalling is initiated by a group of membrane-bound receptors with similarity to two-component systems. ERS1 belongs, together with ETR1, to subfamily 1, which plays a predominant role in ethylene signalling. The dimerization domain of ERS1 was crystallized in space groups C222(1) and P2(1)2(1)2, with two and four molecules per asymmetric unit, respectively. The crystals diffracted X-ray radiation to 1.9 Šresolution.

Cloning, overexpression, purification and preliminary X-ray analysis of the catalytic domain of the ethylene receptor ETR1 from Arabidopsis thaliana.

Ethylene is a gaseous plant hormone which controls many aspects of plant growth and development. It is perceived by membrane-bound receptors with a similarity to bacterial two-component systems. The catalytic and ATP-binding domain of the histidine kinase domain of ETR1 from Arabidopsis thaliana has been cloned, overexpressed and crystallized. The protein was crystallized together with various nucleotides. Crystals obtained in the presence of ADP belonged to space group I222 or I2(1)2(1)2(1) with one molecule per asymmetric unit. They diffracted X-ray radiation to beyond 1.85 Šresolution.

Optimization of protein buffer cocktails using Thermofluor.

The stability and homogeneity of a protein sample is strongly influenced by the composition of the buffer that the protein is in. A quick and easy approach to identify a buffer composition which increases the stability and possibly the conformational homogeneity of a protein sample is the fluorescence-based thermal-shift assay (Thermofluor). Here, a novel 96-condition screen for Thermofluor experiments is presented which consists of buffer and additive parts. The buffer screen comprises 23 different buffers and the additive screen includes small-molecule additives such as salts and nucleotide analogues. The utilization of small-molecule components which increase the thermal stability of a protein sample frequently results in a protein preparation of higher quality and quantity and ultimately also increases the chances of the protein crystallizing.

High-resolution structure of Bombyx mori lipoprotein 7: crystallographic determination of the identity of the protein and its potential role in detoxification.

Three crystal structures of a lipoprotein (Bmlp7) of unknown function, a member of the 30 kDa lipoprotein family from mulberry silkworm (Bombyx mori L.) haemolymph, have been determined. The 1.33 Å resolution structure is an excellent example of how a precise crystallographic study can contribute to protein identification. The correct sequence of this haemolymph-isolated protein was assigned thanks to superb-quality electron-density maps. Two unexpected cadmium cations were found in this crystal structure [Bmlp7-I(Cd)] and their presence may be connected to a detoxification mechanism in this insect. For a comparison of the metal-binding sites, the crystal structure of a platinum complex (Bmlp7-Pt) was also solved at 1.94 Å resolution. The third (2.50 Å resolution) structure, of the native protein harvested in a different season (Bmlp7-II), corresponds to a different polymorph with an altered pattern of intermolecular interactions and with a total absence of cadmium ions and highlights the possible involvement of Bmlp7 in the response to environmental pollution. The N-terminal domain of Bmlp7 has a fold resembling a clockwise spiral created by six helices and can be classified as a VHS domain. The C-terminal domain is folded as a ß-trefoil. The biological function of Bmlp7 is unknown, but its structural homology to sugar-binding proteins suggests that, in analogy to other 30 kDa haemolymph lipoproteins, it could play a role as an anti-apoptotic factor or function in the immune response of the insect to fungal infections.

Cloning, expression, purification, crystallization and preliminary X-ray diffraction analysis of succinyl-diaminopimelate desuccinylase (Rv1202, DapE) from Mycobacterium tuberculosis.

Succinyl-diaminopimelate desuccinylase from Mycobacterium tuberculosis (DapE, Rv1202) has been cloned, heterologously expressed in Escherichia coli and purified using standard chromatographic techniques. Diffraction-quality crystals were obtained at acidic pH from ammonium sulfate and PEG and diffraction data were collected from two crystals to resolutions of 2.40 and 2.58 Å, respectively. The crystals belonged to the monoclinic space group P2(1), with unit-cell parameters a = 79.7, b = 76.0, c = 82.9 Å, ß = 119°. The most probable content of the asymmetric unit was two molecules of DapE, which would correspond to a solvent content of 56%. Both examined crystals turned out to be pseudo-merohedrally twinned, with twin operator -h, -k, h + l and twin fractions of approximately 0.46 and 0.16, respectively.

Cloning, expression, purification and preliminary X-ray analysis of a putative metagenome-derived lipase.

LipS is a novel thermostable putative lipase that was isolated from a metagenomic library using functional screening methods. The corresponding gene shows high similarity to that encoding a putative but uncharacterized esterase from Symbiobacterium thermophilum IAM14863 (99% nucleotide-sequence similarity). Two different constructs of the recombinant lipase were crystallized. Crystals belonging to space group P4(2)2(1)2 diffracted X-ray radiation to 2.8 Šresolution and crystals belonging to space group P4 diffracted to 2.0 Šresolution. The most probable content of their asymmetric units were two molecules (P4(2)2(1)2) and four or five molecules (P4), respectively.

Single isomorphous replacement phasing of selenomethionine-containing proteins using UV-induced radiation damage.

The most commonly used heavy-atom derivative, selenium, requires the use of a tunable beamline to access the Se K edge for experimental phasing using anomalous diffraction methods, whereas X-ray diffraction experiments for selenium-specific ultraviolet radiation-damage-induced phasing can be performed on fixed-wavelength beamlines or even using in-house X-ray sources. Several nonredundant X-ray diffraction data sets were collected from three different selenomethionine (Mse) derivatized protein crystals at energies far below the absorption edge before and after exposing the crystal to ultraviolet (UV) radiation using 266 nm lasers of flux density 1.7 × 10¹5 photons s⁻¹â€…mm⁻² for 10-50 min. A detailed analysis revealed that significant changes in diffracted intensities were induced by ultraviolet irradiation whilst retaining crystal isomorphism. These intensity changes allowed the crystal structures to be solved by the radiation-damage-induced phasing (RIP) technique. Inspection of the crystal structures and electron-density maps demonstrated that covalent bonds between selenium and carbon at all sites located in the core of the proteins or in a hydrophobic environment were much more susceptible to UV radiation-induced cleavage than other bonds typically present in Mse proteins. The rapid UV radiation-induced bond cleavage opens a reliable new paradigm for phasing when no tunable X-ray source is available. The behaviour of Mse derivatives of various proteins provides novel insights and an initial basis for understanding the mechanism of selenium-specific UV radiation damage.

Cloning, expression, purification and preliminary X-ray analysis of the protein kinase domain of constitutive triple response 1 (CTR1) from Arabidopsis thaliana.

Ethylene, a gaseous plant hormone, is perceived by a group of membrane-bound receptors. Constitutive triple response 1 (CTR1) from Arabidopsis thaliana directly interacts with ethylene receptors and thus links signal reception to the intracellular signalling pathway. The C-terminal protein kinase domain of CTR1 has been crystallized in its wild-type form and as a kinase-dead mutant. The wild-type crystals diffracted X-ray radiation to 3 Šresolution and the crystals of the kinase-dead mutant diffacted to 2.5 Šresolution. The crystals belonged to space groups P4(1)2(1)2 and P4(2)2(1)2, respectively, with two molecules per asymmetric unit in both cases.

Cloning, expression, purification, crystallization and preliminary X-ray diffraction analysis of the regulatory domain of aspartokinase (Rv3709c) from Mycobacterium tuberculosis.

The regulatory domain of Mycobacterium tuberculosis aspartokinase (Mtb-AK, Mtb-Ask, Rv3709c) has been cloned, heterologously expressed in Escherichia coli and purified using standard chromatographic techniques. Screening for initial crystallization conditions using the regulatory domain (AK-ß) in the presence of the potential feedback inhibitor threonine identified four conditions which yielded crystals suitable for X-ray diffraction analysis. From these four conditions five different crystal forms of Mtb-AK-ß resulted, three of which belonged to the orthorhombic system, one to the tetragonal system and one to the monoclinic system. The highest resolution (1.6 Å) was observed for a crystal form belonging to space group P2(1)2(1)2(1), with unit-cell parameters a=53.70, b=63.43, c=108.85 Šand two molecules per asymmetric unit.

Cloning, expression, purification and crystallization as well as X-ray fluorescence and preliminary X-ray diffraction analyses of human ADP-ribosylhydrolase 1.

Human ADP-ribosylhydrolase 1 (hARH1, ADPRH) cleaves the glycosidic bond of ADP-ribose attached to an Arg residue of a protein. hARH1 has been cloned, expressed heterologously in Escherichia coli, purified and crystallized in complex with K(+) and ADP. The orthorhombic crystals contained one monomer per asymmetric unit, exhibited a solvent content of 43% and diffracted X-rays to a resolution of 1.9 A. A prerequisite for obtaining well diffracting crystals was the performance of X-ray fluorescence analysis on poorly diffracting apo hARH1 crystals, which revealed the presence of trace amounts of K(+) in the crystal. Adding K-ADP to the crystallization cocktail then resulted in a crystal of different morphology and with dramatically improved diffraction properties.

Cloning, expression, purification, crystallization and preliminary X-ray crystallographic analysis of interleukin-4-inducing principle from Schistosoma mansoni eggs (IPSE/alpha-1).

The interleukin-4-inducing principle from Schistosoma mansoni eggs (IPSE/alpha-1) triggers the release of large amounts of interleukin-4 from human blood basophils, thus presumably playing an immunomodulatory role during schistosome infection. IPSE/alpha-1 was crystallized and a native X-ray data set was collected to 1.66 A resolution from a single crystal at 100 K using synchrotron radiation. The crystal belonged to space group P6(1) or P6(5), with one molecule per asymmetric unit.

Cloning, expression, purification, crystallization and preliminary X-ray crystallographic analysis of isocitrate dehydrogenase 2 (Rv0066c) from Mycobacterium tuberculosis.

Isocitrate dehydrogenase 2 (Icd-2, Rv0066c) from Mycobacterium tuberculosis was cloned and heterologously expressed in Escherichia coli. The protein was purified by affinity and size-exclusion chromatography and crystallized. A complete data set has been collected and reduced to 3.25 A resolution in space group C2. Preliminary diffraction data analysis suggests a complex packing with at least six molecules in the asymmetric unit.

Structure of mouse ADP-ribosylhydrolase 3 (mARH3).

ADP-ribosylation is a reversible and covalent post-translational modification in which the attachment of ADP-ribose is catalyzed by ADP-ribosyltransferases and the removal of ADP-ribose is catalyzed by ADP-ribosylhydrolases. ADP-ribosylhydrolase 3 from mouse, consisting of 347 amino-acid residues, has been cloned, purified and crystallized. The three-dimensional structure has been resolved at a resolution of 1.8 A. The structure constitutes a compact all-alpha-helical protein with two Mg(2+) ions located in the active-site crevice. A structural comparison of mouse ADP-ribosylhydrolase 3 with its human orthologue shows a high degree of structural similarity. Furthermore, four prokaryotic proteins deposited in the PDB could be identified as being structurally related.

Cloning, expression, purification, crystallization and preliminary X-ray crystallographic analysis of initiation factor 1 from Mycobacterium tuberculosis.

Initiation factor 1 (IF-1; Rv3462c) from Mycobacterium tuberculosis, a component of the 30S initiation complex, was cloned and heterologously expressed in Escherichia coli. The protein was purified by affinity and size-exclusion chromatography and crystallized. A complete data set has been collected to high resolution. The crystals belonged to space group P2(1)2(1)2, with two molecules per asymmetric unit which are related by translational symmetry.

Cloning, expression, purification, crystallization and preliminary X-ray diffraction analysis of human ARH3, the first eukaryotic protein-ADP-ribosylhydrolase.

ADP-ribosylhydrolases catalyze the release of ADP-ribose from ADP-ribosylated proteins via hydrolysis of the glycosidic bond between ADP-ribose and a specific amino-acid residue in a target protein. Human ADP-ribosylhydrolase 3, consisting of 347 amino-acid residues, has been cloned and heterologously expressed in Escherichia coli, purified and crystallized in two different space groups. Preliminary X-ray diffraction studies yielded excellent diffraction data to a resolution of 1.6 A.