Cell Dimensionsa Research Articles

A Structural Determinant for the Control of PIP2 Sensitivity in G Protein-gated Inward Rectifier K+ Channels

Inward rectifier K+ (Kir) channels are activated by phosphatidylinositol-(4,5)-bisphosphate (PIP2), but G protein-gated Kir (KG) channels further require either G protein βγ subunits (Gβγ) or intracellular Na+ for their activation. To reveal the mechanism(s) underlying this regulation, we compared the crystal structures of the cytoplasmic domain of KG channel subunit Kir3.2 obtained in the presence and the absence of Na+. The Na+-free Kir3.2, but not the Na+-plus Kir3.2, possessed an ionic bond connecting the N terminus and the CD loop of the C terminus. Functional analyses revealed that the ionic bond between His-69 on the N terminus and Asp-228 on the CD loop, which are known to be critically involved in Gβγ- and Na+-dependent activation, lowered PIP2 sensitivity. The conservation of these residues within the KG channel family indicates that the ionic bond is a character that maintains the channels in a closed state by controlling the PIP2 sensitivity.

Peroxisomal Plant 3-Ketoacyl-CoA Thiolase Structure and Activity Are Regulated by a Sensitive Redox Switch

The breakdown of fatty acids, performed by the beta-oxidation cycle, is crucial for plant germination and sustainability. beta-Oxidation involves four enzymatic reactions. The final step, in which a two-carbon unit is cleaved from the fatty acid, is performed by a 3-ketoacyl-CoA thiolase (KAT). The shortened fatty acid may then pass through the cycle again (until reaching acetoacetyl-CoA) or be directed to a different cellular function. Crystal structures of KAT from Arabidopsis thaliana and Helianthus annuus have been solved to 1.5 and 1.8 A resolution, respectively. Their dimeric structures are very similar and exhibit a typical thiolase-like fold; dimer formation and active site conformation appear in an open, active, reduced state. Using an interdisciplinary approach, we confirmed the potential of plant KATs to be regulated by the redox environment in the peroxisome within a physiological range. In addition, co-immunoprecipitation studies suggest an interaction between KAT and the multifunctional protein that is responsible for the preceding two steps in beta-oxidation, which would allow a route for substrate channeling. We suggest a model for this complex based on the bacterial system.

Potassium-activated GTPase Reaction in the G Protein-coupled Ferrous Iron Transporter B

FeoB is a prokaryotic membrane protein responsible for the import of ferrous iron (Fe(2+)). A defining feature of FeoB is that it includes an N-terminal 30-kDa soluble domain with GTPase activity, which is required for iron transport. However, the low intrinsic GTP hydrolysis rate of this domain appears to be too slow for FeoB either to function as a channel or to possess an active Fe(2+) membrane transport mechanism. Here, we present crystal structures of the soluble domain of FeoB from Streptococcus thermophilus in complex with GDP and with the GTP analogue derivative 2'-(or -3')-O-(N-methylanthraniloyl)-beta,gamma-imidoguanosine 5'-triphosphate (mant-GMPPNP). Unlike recent structures of the G protein domain, the mant-GMPPNP-bound structure shows clearly resolved, active conformations of the critical Switch motifs. Importantly, biochemical analyses demonstrate that the GTPase activity of FeoB is activated by K(+), which leads to a 20-fold acceleration in its hydrolysis rate. Analysis of the structure identified a conserved asparagine residue likely to be involved in K(+) coordination, and mutation of this residue abolished K(+)-dependent activation. We suggest that this, together with a second asparagine residue that we show is critical for the structure of the Switch I loop, allows the prediction of K(+)-dependent activation in G proteins. In addition, the accelerated hydrolysis rate opens up the possibility that FeoB might indeed function as an active transporter.

Dimerization and Protein Binding Specificity of the U2AF Homology Motif of the Splicing Factor Puf60

PUF60 is an essential splicing factor functionally related and homologous to U2AF(65). Its C-terminal domain belongs to the family of U2AF (U2 auxiliary factor) homology motifs (UHM), a subgroup of RNA recognition motifs that bind to tryptophan-containing linear peptide motifs (UHM ligand motifs, ULMs) in several nuclear proteins. Here, we show that the Puf60 UHM is mainly monomeric in physiological buffer, whereas its dimerization is induced upon the addition of SDS. The crystal structure of PUF60-UHM at 2.2 angstroms resolution, NMR data, and mutational analysis reveal that the dimer interface is mediated by electrostatic interactions involving a flexible loop. Using glutathione S-transferase pulldown experiments, isothermal titration calorimetry, and NMR titrations, we find that Puf60-UHM binds to ULM sequences in the splicing factors SF1, U2AF65, and SF3b155. Compared with U2AF65-UHM, Puf60-UHM has distinct binding preferences to ULMs in the N terminus of SF3b155. Our data suggest that the functional cooperativity between U2AF65 and Puf60 may involve simultaneous interactions of the two proteins with SF3b155.

Crystal Structure of Human Estrogen-related Receptor α in Complex with a Synthetic Inverse Agonist Reveals Its Novel Molecular Mechanism

Inverse agonists of the constitutively active human estrogen-related receptor alpha (ERRalpha, NR3B1) are of potential interest for several disease indications (e.g. breast cancer, metabolic diseases, or osteoporosis). ERRalpha is constitutively active, because its ligand binding pocket (LBP) is practically filled with side chains (in particular with Phe(328), which is replaced by Ala in ERRbeta and ERRgamma). We present here the crystal structure of the ligand binding domain of ERRalpha (containing the mutation C325S) in complex with the inverse agonist cyclohexylmethyl-(1-p-tolyl-1H-indol-3-ylmethyl)-amine (compound 1a), to a resolution of 2.3A(.) The structure reveals the dramatic multiple conformational changes in the LBP, which create the necessary space for the ligand. As a consequence of the new side chain conformation of Phe(328) (on helix H3), Phe(510)(H12) has to move away, and thus the activation helix H12 is displaced from its agonist position. This is a novel mechanism of H12 inactivation, different from ERRgamma, estrogen receptor (ER) alpha, and ERbeta. H12 binds (with a surprising binding mode) in the coactivator groove of its ligand binding domain, at a similar place as a coactivator peptide. This is in contrast to ERRgamma but resembles the situation for ERalpha (raloxifene or 4-hydroxytamoxifen complexes). Our results explain the novel molecular mechanism of an inverse agonist for ERRalpha and provide the basis for rational drug design to obtain isotype-specific inverse agonists of this potential new drug target. Despite a practically filled LBP, the finding that a suitable ligand can induce an opening of the cavity also has broad implications for other orphan nuclear hormone receptors (e.g. the NGFI-B subfamily).

Structural and Biophysical Coupling of Heparin and Activin Binding to Follistatin Isoform Functions

Follistatin (FS) regulates transforming growth factor-beta superfamily ligands and is necessary for normal embryonic and ovarian follicle development. Follistatin is expressed as two splice variants (FS288 and FS315). Previous studies indicated differences in heparin binding between FS288 and FS315, potentially influencing the physiological functions and locations of these isoforms. We have determined the structure of the FS315-activin A complex and quantitatively compared heparin binding by the two isoforms. The FS315 complex structure shows that both isoforms inhibit activin similarly, but FS315 exhibits movements within follistatin domain 3 (FSD3) apparently linked to binding of the C-terminal extension. Surprisingly, the binding affinities of FS288 and FS315 for heparin are similar at lower ionic strengths with FS315 binding decreasing more sharply as a function of salt concentration. When bound to activin, FS315 binds heparin similarly to the FS288 isoform, consistent with the structure of the complex, in which the acidic residues of the C-terminal extension cannot interact with the heparin-binding site. Activin-induced binding of heparin is unique to the FS315 isoform and may stimulate clearance of FS315 complexes.

The Molecular Basis of Glyphosate Resistance by an Optimized Microbial Acetyltransferase

GAT is an N-acetyltransferase from Bacillus licheniformis that was optimized by gene shuffling for acetylation of the broad spectrum herbicide, glyphosate, forming the basis of a novel mechanism of glyphosate tolerance in transgenic plants (Castle, L. A., Siehl, D. L., Gorton, R., Patten, P. A., Chen, Y. H., Bertain, S., Cho, H. J., Duck, N., Wong, J., Liu, D., and Lassner, M. W. (2004) Science 304, 1151-1154). The 1.6-A resolution crystal structure of an optimized GAT variant in ternary complex with acetyl coenzyme A and a competitive inhibitor, 3-phosphoglyerate, defines GAT as a member of the GCN5-related family of N-acetyltransferases. Four active site residues (Arg-21, Arg-73, Arg-111, and His-138) contribute to a positively charged substrate-binding site that is conserved throughout the GAT subfamily. Structural and kinetic data suggest that His-138 functions as a catalytic base via substrate-assisted deprotonation of the glyphosate secondary amine, whereas another active site residue, Tyr-118, functions as a general acid. Although the physiological substrate is unknown, native GAT acetylates D-2-amino-3-phosphonopropionic acid with a kcat/Km of 1500 min-1 mM-1. Kinetic data show preferential binding of short analogs to native GAT and progressively better binding of longer analogs to optimized variants. Despite a 200-fold increase in kcat and a 5.4-fold decrease in Km for glyphosate, only 4 of the 21 substitutions present in R7 GAT lie in the active site. Single-site revertants constructed at these positions suggest that glyphosate binding is optimized through substitutions that increase the size of the substrate-binding site. The large improvement in kcat is likely because of the cooperative effects of additional substitutions located distal to the active site.

Structure of Human Eg5 in Complex with a New Monastrol-based Inhibitor Bound in the R Configuration

Drugs that target mitotic spindle proteins have been proven useful for tackling tumor growth. Eg5, a kinesin-5 family member, represents a potential target, since its inhibition leads to prolonged mitotic arrest through the activation of the mitotic checkpoint and apoptotic cell death. Monastrol, a specific dihydropyrimidine inhibitor of Eg5, shows stereo-specificity, since predominantly the (S)-, but not the (R)-, enantiomer has been shown to be the biologically active compound in vitro and in cell-based assays. Here, we solved the crystal structure (2.7A) of the complex between human Eg5 and a new keto derivative of monastrol (named mon-97), a potent antimitotic inhibitor. Surprisingly, we identified the (R)-enantiomer bound in the active site, and not, as for monastrol, the (S)-enantiomer. The absolute configuration of this more active (R)-enantiomer has been unambiguously determined via chemical correlation and x-ray analysis. Unexpectedly, both the R- and the S-forms inhibit Eg5 ATPase activity with IC(50) values of 110 and 520 nM (basal assays) and 150 nm and 650 nm (microtubule-stimulated assays), respectively. However, the difference was large enough for the protein to select the (R)- over the (S)-enantiomer. Taken together, these results show that in this new monastrol family, both (R)- and (S)-enantiomers can be active as Eg5 inhibitors. This considerably broadens the alternatives for rational drug design.

Unveiling a Hidden Folding Intermediate in c-Type Cytochromes by Protein Engineering

Several investigators have highlighted a correlation between the basic features of the folding process of a protein and its topology, which dictates the folding pathway. Within this conceptual framework we proposed that different members of the cytochrome c (cyt c) family share the same folding mechanism, involving a consensus partially structured state. Pseudomonas aeruginosa cyt c(551) (Pa cyt c(551)) folds via an apparent two-state mechanism through a high energy intermediate. Here we present kinetic evidence demonstrating that it is possible to switch its folding mechanism from two to three state, stabilizing the high energy intermediate by rational mutagenesis. Characterization of the folding kinetics of one single-site mutant of the Pa cyt c(551) (Phe(7) to Ala) indeed reveals an additional refolding phase and a fast unfolding process which are explained by the accumulation of a partially folded species. Further kinetic analysis highlights the presence of two parallel processes both leading to the native state, suggesting that the above mentioned species is a non obligatory on-pathway intermediate. Determination of the crystallographic structure of F7A shows the presence of an extended internal cavity, which hosts three "bound" water molecules and a H-bond in the N-terminal helix, which is shorter than in the wild type protein. These two features allow us to propose a detailed structural interpretation for the stabilization of the native and especially the intermediate states induced by a single crucial mutation. These results show how protein engineering, x-ray crystallography and state-of-the-art kinetics concur to unveil a folding intermediate and the structural determinants of its stability.

A Comparative Study of Uracil-DNA Glycosylases from Human and Herpes Simplex Virus Type 1

Uracil-DNA glycosylase (UNG) is the key enzyme responsible for initiation of base excision repair. We have used both kinetic and binding assays for comparative analysis of UNG enzymes from humans and herpes simplex virus type 1 (HSV-1). Steady-state fluorescence assays showed that hUNG has a much higher specificity constant (k(cat)/K(m)) compared with the viral enzyme due to a lower K(m). The binding of UNG to DNA was also studied using a catalytically inactive mutant of UNG and non-cleavable substrate analogs (2'-deoxypseudouridine and 2'-alpha-fluoro-2'-deoxyuridine). Equilibrium DNA binding revealed that both human and HSV-1 UNG enzymes bind to abasic DNA and both substrate analogs more weakly than to uracil-containing DNA. Structure determination of HSV-1 D88N/H210N UNG in complex with uracil revealed detailed information on substrate binding. Together, these results suggest that a significant proportion of the binding energy is provided by specific interactions with the target uracil. The kinetic parameters for human UNG indicate that it is likely to have activity against both U.A and U.G mismatches in vivo. Weak binding to abasic DNA also suggests that UNG activity is unlikely to be coupled to the subsequent common steps of base excision repair.

Pseudomonas aeruginosa LD-Carboxypeptidase, a Serine Peptidase with a Ser-His-Glu Triad and a Nucleophilic Elbow*

LD-Carboxypeptidases (EC 3.4.17.13) are named for their ability to cleave amide bonds between l- and d-amino acids, which occur naturally in bacterial peptidoglycan. They are specific for the link between meso-diaminopimelic acid and d-alanine and therefore degrade GlcNAc-MurNAc tetrapeptides to the corresponding tripeptides. As only the tripeptides can be reused as peptidoglycan building blocks, ld-carboxypeptidases are thought to play a role in peptidoglycan recycling. Despite the pharmaceutical interest in peptidoglycan biosynthesis, the fold and catalytic type of ld-carboxypeptidases are unknown. Here, we show that a previously uncharacterized open reading frame in Pseudomonas aeruginosa has ld-carboxypeptidase activity and present the crystal structure of this enzyme. The structure shows that the enzyme consists of an N-terminal beta-sheet and a C-terminal beta-barrel domain. At the interface of the two domains, Ser(115) adopts a highly strained conformation in the context of a strand-turn-helix motif that is similar to the "nucleophilic elbow" in alphabeta-hydrolases. Ser(115) is hydrogen-bonded to a histidine residue, which is oriented by a glutamate residue. All three residues, which occur in the order Ser-Glu-His in the amino acid sequence, are strictly conserved in naturally occurring ld-carboxypeptidases and cannot be mutated to alanines without loss of activity. We conclude that ld-carboxypeptidases are serine peptidases with Ser-His-Glu catalytic triads.

New magnetic materials obtained by ion-exchange reactions from non-magnetic layeredperovskites

New layered magnetic materials,(MCl)Ca2Ta3O10 (M = Cu,Fe), have been prepared by ion-exchange reactions of non-magnetic perovskite derivatives,ACa2Ta3O10 (A = Rb,Li), in corresponding anhydrous molten salts. Powder x-ray diffraction patterns of theproducts are successfully indexed assuming tetragonal symmetry with cell dimensionsa = 3.829 Å andc = 15.533 Å for Cu,and a = 3.822 Å andc = 15.672 Å for Fe. Beingseparated by the Ca2Ta3O10 triple-layer perovskite slabs, the transition-metal chloride (MCl) network provides atwo-dimensional magnetic lattice. Magnetic susceptibility measurements show that(CuCl)Ca2Ta3O10 is in an antiferromagnetic state below 8 K, while(FeCl)Ca2Ta3O10 has two anomalies at 91 and 125 K, suggesting successive phase transitions due togeometrical spin frustration.

Synthesis of [(C5H5Y (η2-PzMe2)(η-PzMe2)]2 and [Y(η2-PzMe2)2(η-PzMe2)(η-THF)]2 and the insertion of Me2SiO into the Y-N bond

3,5-Dimethylpyrazole (HPzMe2) reacted with (C5H5)3Y in THF to yield dinuclear complexes [(C5H5)Y-(η2-PzMe2)(η-PzMe2)]2 (I) and [Y(η2-PzMe2)2(η-PzMe2)-(η-THF)]2 (II), revealing a new method for synthesizing tris(pyrazolate) complexes of lanthanide metals. The X-ray crystallographic analysis showed that complex II crystallizes in space groupP ·· − , with unit cell dimensionsa = 1.0798(1),b = 1.0818(1),c = 1.1313(1) nm, α = 76.914(2)°, β = 68.940(2)°, γ= 60.510(2)°,V= 1.0715(2) nm3, Z= 1. The finalR factor is 0.0445. The investigation results showed that Me2SiO can only be inserted into the Y-N (bridging) bond of complex I to form [(C5H5)Y(η2-PzMe2)(η-OSiMe2 PzMe2)]2 (III), but cannot be inserted into the Y-N (bridging) bond of complex II due to the bulky crowding of the tetraple bridge structure.

Crystal and Electronic Structures and Linear Optics of Strontium Pyroborate

The compound Sr2B2O5has been synthesized by high temperature solution reaction. It crystallizes in the monoclinic space groupP21/cwith cell dimensionsa=7.719(4),b=5.341(1),c=11.873(2)Å,β=92.71(2)°,V=488.9(3) Å3, andZ=4,Dcalc=3.76 g/cm3. The structure comprises SrO7and SrO6polyhedra and B2O5groups. The electronic structure has been calculated by the INDO/S method for this compound, and the dynamic refractive indices have been obtained in terms of INDO/SCI following combination with the sum-over-states method. The calculated energy gap is 4.26 eV between the upper valence band and lower conduction band, and the calculated average refractive index is 1.791 at a wavelength of 1.065 μm. The charge transfers from O2−anion orbitals to Sr2+cation orbitals make the significant contributions to linear polarizability in terms of analyses of atomic state density contributing to the valence and conduction bands.

The crystal and molecular structures of some nickel(ll)bis(O-alkyldithiocarbonate)s and nickel(II)bis(N,N-dialkyldithiocarbamate)s: an evaluation of the coordination potential of 1,1-dithiolate ligands in their nickel(II) complexes

AbstractThe crystal and molecular structures of four complexes of the general formula Ni(S2COR)2and two with the general formula Ni(S2CNR2)2have been determined. The brown crystals of [Ni(S2COMe)2], investigated at 293 K, are monoclinic, space groupP21/cwith unit cell dimensionsa= 6.357(4) Å,b= 13.755(10) Å,c= 10.566(3) Å,β= 97.20(3)°,Z= 4 andDx= 1.979 Mg m−3. The brown crystals of [Ni(S2COiBu)2], (293 K) are triclinic, space groupP{unk] with unit cell dimensionsa= 8.224(7) Å,b= 8.722(3) Å,c= 6.139(4) Å,α= 98.99(4)°,β= 105.36(5)°,γ= 109.10(4)°,Z= 1 andDx= 1.534 Mg m−3. Crystals of brown [Ni(S2COHex)2], (200 K) are triclinic, space groupP[unk] with unit cell dimensionsa= 7.566(2) Å,b= 10.713(4) Å,c= 6.779(2) Å,α= 97.73(3)°,β= 111.22(2)°,γ= 103.19(2)°,Z= 1 andDx= 1.417 Mg m−3. Crystals of brown [Ni(S2COCy)2], (200 K) are triclinic, space groupP[unk] with unit cell dimensionsa= 9.89(1) Å,b= 10.102(7) Å,c= 9.850(7) Å,α= 110.83(5)°, β= 107.19(7)°,γ= 87.28(9)°,Z= 2 andDx= 1.550 Mg m−3. Crystals of brown [Ni(S2CNCy2)2], (200 K) are triclinic, space groupP[unk] with unit cell dimensionsa= 11.551(5) Å,b= 14.651 (7) Å,c= 9.872(5) Å,α= 102.46(5)°,β= 114.78(3)°,γ= 89.65(4)°,Z= 2 andDx= 1.287 Mg m−3. The colorless crystals of [Ni(S2CN(Et)Cy)2] (200 K) are monoclinic, space groupP21/cwith unit cell dimensionsa= 8.534(4) Å,b= 12.087(4) Å,c= 11.109(4) Å,β= 95.54(3)°,Z= 2 andDx= 1.349 Mg m−3. The structures were solved by direct methods and each refined by a full-matrix least-squares procedure to finalR= 0.047 using 1149 reflections for [Ni(S2COMe)2]; toR= 0.040 using 1239 reflections for [Ni(S2COiBu)2]; toR= 0.050 using 1664 reflections for [Ni(S2COHex)2]; to finalR= 0.035 for 2956 reflections for [Ni(S2COCy)2]; to finalR= 0.055 for 3468 reflections for [Ni(S2CNCy2)2]; and to finalR= 0.031 for 1827 reflections for [Ni(S2CN(Et)Cy)2]. A systematic evaluation of the coordination geometries in these and related complexes indicate that there is little variation in the Ni-atom geometries which are invariably square planar, defined by a S4donor set. Further, there is no apparent systematic variation in the Ni–S bond distances that can be correlated with the nature of the individual xanthate (−S2COR) and dithiocarbamate C(−S2CNR2) ligands as moderated by the electronic/steric profiles of R. Rather, variations in the Ni–S bond distances are ascribed to i) intramolecular interactions between the sulfur atoms and the R substituents and, ii) intermolecular forces.

Crystallization and Preliminary X-Ray Analysis of Active Site-Inhibited Human Coagulation Factor VIIa (des-Gla)

Human coagulation factor VIIai that lacks the Gla domain (residues 1–44) has been prepared, purified, and crystallised. First, recombinant factor VII was activated to form factor VIIa, the active site was then inhibited with 1,5-dansyl-Glu-Gly-Arg-chloromethyl ketone, and finally the Gla domain was removed by chymotryptic digestion, yielding factor VIIai (des-Gla). After further purification single crystals suitable for x-ray analysis were obtained by vapour diffusion. Crystals of factor VIIai (des-Gla) belong to the tetragonal space groupP41212 orP43212 with unit cell dimensionsa=b= 94.85 Å,c= 114.30 Å, contain one molecule per asymmetric unit, and diffract to 2.3-Å resolution when exposed to synchrotron radiation.

Thermal Behavior of Zinc Phenylphosphonate and Structure Determination ofγ-Zn2P2O7from X-Ray Powder Diffraction Data

The thermal behavior of zinc phenylphosphonate has been studied by temperature-dependent X-ray powder diffraction and thermo-gravimetry in the temperature range 19–600°C. The different phases occurring during the decomposition have been identified, i.e., the anhydrous phase and the three successive polymorphic varieties of Zn2P2O7. The first one is amorphous,δ-Zn2P2O7is poorly crystalline, andγ-Zn2P2O7is a metastable phase. The last transforms into theβvariety at higher temperature. The crystal structure ofγ-Zn2P2O7has been solvedab initiofrom powder diffraction data collected with conventional monochromatic X-rays. The symmetry is orthorhombic with the cell dimensionsa=4.9504(5) Å,b=13.335(2) Å,c=16.482(3) Å, space groupPbcm,Z=8. The structure consists of infinite corrugated chains of ZnO5trigonal bipyramids, running along [001]. These chains are linked together by P2O7groups in the two other directions. The P2O4−7anions display low angles and an eclipsed conformation, contrary to theαandβphases.

Synthesis, Crystal Structure, and Properties of Polymeric Rb12Nb6Se35, a Novel Ternary Niobium Selenide Consisting of Infinite Anionic Chains Built Up by Nb2Se11Units Containing an Uncommon Se4−3-Fragment

Rb12Nb6Se35is the first ternary niobium polyselenide composed of infinite anionic chains. These are well separated by rubidium cations. It crystallizes in the orthorhombic space groupPbcnwith unit cell dimensionsa=8.5811(1) Å,b=13.7152(1) Å,c=56.5225(4) Å, andZ=4. The least-squares refinement againstF2with anisotropic displacement parameters for all atoms yieldsR1=5.78 and wR2=12.81. The anionic polymeric chains are arranged in layers parallel to the (010) plane, and successive planes are rotated by 35° against each other. Nb2Se11units composed of two face-sharing NbSe7pentagonal bipyramids are the building blocks of the structure. They are interconnected by Se2−2and Se2−3polyanions, giving rise to infinite1∞[Nb6Se35]12−chains. Within the Nb2Se11units an unusual nearly linear Se3fragment is found which must be formulated as Se4−3.

Preliminary Crystallographic Study of GlutathioneS-Transferase Fused with the Nuclear Matrix Targeting Signal of the Transcription Factor AML-1/CBF-α2

A glutathioneS-transferase fused with the nuclear matrix targeting signal (GST–NMTS) of AML-1/CBF-α2 has been crystallized by the vapor diffusion method using polyethylene glycol (PEG) as the precipitant. The NMTS is a 31-amino-acid signal peptide that can target the AML-1/CBF-α2 protein to the nuclear matrix. The crystal belongs to tetragonal space groupP43212 with unit cell dimensionsa=b= 93.4 Å,c= 57.6 Å. There is one GST-fusion protein per asymmetric unit. Crystals diffracted to at least 2.7 Å and are appropriate for structure determination.

Synthesis and Structure Determination of La8Ti10S24O4

The new compound La8Ti10S24O4has been prepared from a mixture of La2Ti2O7and La2O3(in a 5:1 ratio) heated at 1200°C under a H2S gas flow. This new quaternary phase was obtained due to an incomplete sulfidizing process. Single-crystal X-ray diffraction studies show that La8Ti10S24O4crystallizes in space groupP4/mmm, withZ=1, in a cell of dimensionsa=b=10.421 Å andc=8.384 Å. Least-squares refinement converged to values ofR=0.045 andRw=0.048. The structure can be viewed as a stacking of two types of layers along the c→ axis. These layers are built up from infinite rutile-like chains (Ti octahedra) that cross perpendicularly. La atoms, in a tricapped prismatic coordination, are located in tunnels that develop parallel to the c→ direction.