Complex Domain Structure Research Articles

Ferromagnetic domain nucleation and growth in colossal magnetoresistive manganite

Colossal magnetoresistance is a dramatic decrease in resistivity caused by applied magnetic fields, and has been the focus of much research because of its potential for magnetic data storage using materials such as manganites. Although extensive microscopy and theoretical studies have shown that colossal magnetoresistance involves competing insulating and ferromagnetic conductive phases, the mechanism underlying the effect remains unclear. Here, by directly observing magnetic domain walls and flux distributions using cryogenic Lorentz microscopy and electron holography, we demonstrate that an applied magnetic field assists nucleation and growth of an ordered ferromagnetic phase. These results provide new insights into the evolution dynamics of complex domain structures at the nanoscale, and help to explain anomalous phase separation phenomena that are relevant for applications. Our approach can also be used to determine magnetic parameters of nanoscale regions, such as magnetocrystalline anisotropy and exchange stiffness, without bulk magnetization results or neutron scattering data.

Structural basis for specific recognition of Lys 63-linked polyubiquitin chains by NZF domains of TAB2 and TAB3

TAB2 and TAB3 activate the Jun N-terminal kinase and nuclear factor-kappaB pathways through the specific recognition of Lys 63-linked polyubiquitin chains by its Npl4 zinc-finger (NZF) domain. Here we report crystal structures of the TAB2 and TAB3 NZF domains in complex with Lys 63-linked diubiquitin at 1.18 and 1.40 A resolutions, respectively. Both NZF domains bind to the distal ubiquitin through a conserved Thr-Phe dipeptide that has been shown to be important for the interaction of the NZF domain of Npl4 with monoubiquitin. In contrast, a surface specific to TAB2 and TAB3 binds the proximal ubiquitin. Both the distal and proximal binding sites of the TAB2 and TAB3 NZF domains recognize the Ile 44-centred hydrophobic patch on ubiquitin but do not interact with the Lys 63-linked isopeptide bond. Mutagenesis experiments show that both binding sites are required to enable binding of Lys 63-linked diubiquitin. We therefore propose a mechanism for the recognition of Lys 63-linked polyubiquitin chains by TAB2 and TAB3 NZF domains in which diubiquitin units are specifically recognized by a single NZF domain.

Analysis of Magnetic Domain Patterns and Vector Hysteresis Loops in Dot/Antidot Structures

Dot and antidot structures have been prepared by means of optical lithography on Co-Fe-Si-B and permalloy thin films with thickness of 100 nm and 50 nm respectively. Magnetic force microscopy has been employed to study their surface magnetization configuration. Vector vibrating sample magnetometry has been exploited to measure hysteresis loops with the application of an in-plane magnetic field directed at different angles with respect to the dot/antidot arrays. Depending on microstructure geometry and chosen material, different and complex domain structures have been observed and discussed with the support of vector magnetization measurements.

Structure and physiological importance of angiotensin converting enzyme domains

Somatic angiotensin converting enzyme (ACE) consists of two homologous catalytic domains (N- and C-domain), each of which bears an active site exhibiting different biochemical properties. The ACE isoforms consisted of one domain were also detected in mammals. Substantial progress in ACE domain research was achieved during the last years, when crystal their structures were determined. The crystal structures of domains in complex with diverse potent ACE inhibitors provided new insights into structure-based differences of the domain active sites. Physiological functions of ACE are not limited by regulation of the cardiovascular system. Recent evidence suggests that the ACE domains may be also involved into control distinct physiological functions. The C-terminal catalytic domain, playing important role in regulation of blood pressure, catalyzes angiotensin I cleavage in vivo. The N-domain contributes to processing of other bioactive peptides for which it exhibits high affinity. Domain-selective inhibitors able to block selectively either the N- or C-domain of ACE have been developed.

Structural Rearrangement Accompanying Ligand Binding in the GAF Domain of CodY from Bacillus subtilis

The GAF domain is a simple module widespread in proteins of diverse function, including cell signalling proteins and transcription factors. Its structure, typically spanning 150 residues, has three tiers: a basal layer of two or more α-helices, a middle layer of β-pleated sheet and a top layer formed by segments of the polypeptide that connect strands of the β-sheet. In structures of GAF domains in complex with their effectors, these polypeptide segments envelop the ligand, enclosing it in a cavity whose base is formed by the β-sheet, such that ligand binding and release must be accompanied by conformational rearrangements of the distal portion of the structure. Descriptions of binding are presently limited by the absence of a GAF domain for which both liganded and unliganded structures are known. Earlier, we solved the crystal structure of the GAF domain of CodY, a branched-chain amino acid and GTP-responsive regulator of the transcription of stationary-phase and virulence genes in Bacillus, in complexes with isoleucine and valine. Here, we report the structure of this domain in its unliganded form, allowing definition of the structural changes accompanying ligand binding. The core of the protein and its dimerisation interface are essentially unchanged, in agreement with circular dichroism spectroscopy experiments that show that the secondary structure composition is unperturbed by ligand binding. There is however extensive refolding of the binding site loops, with up to 15-Å movements of the coiled segment linking β3 and β4, such that the binding pocket is not formed in the absence of the ligand. The implications of these structural rearrangements for ligand affinity and specificity are discussed. Finally, saturation-transfer-difference NMR spectroscopy showed binding of isoleucine but not that of GTP to the GAF domain, suggesting that the two cofactors do not have a common binding site.

Magnetic Reversal Behaviors of Perpendicular Exchange-Coupled Fe/FePt Bilayer Films

Fe top layers with a thickness t Fe between 1 and 15 nm were deposited on textured FePt(001)/Pt(001)/Cr(002) layers to study the associated exchange coupling effect and their switching behaviors. The deposition of a Fe layer does not change the crystalline structure of the FePt layer. Microstructural analysis reveals that the Fe(200) texture is formed epitaxially on the FePt(001) surface. When t Fe = 1 nm, the remanent coercivity (H cr) remains the same as that without a Fe top layer. The lack of reversible magnetization reveals that the Fe layer is thinner than the critical thickness; the strong coupling force throughout the whole Fe layer facilitates the cooperatively magnetic rotation of Fe and FePt layers. Significant exchange spring was observed in the sample with t Fe = 3 and 5 nm, reducing H cr by 14% and 43% (the maximum reduction), respectively. The results are consistent with the theoretical prediction. As t Fe was increased up to 8 and 12 nm, the exchange spring effect disappeared. Although the two films exhibited similarly reduced H cr values of about 1.5 kOe, the reduction of H cr is caused by the tilt of the magnetic moments rather than the exchange spring. This incline of the moments is caused by the weakened exchange coupling and the complex domain structure. The magnetic reversal was further examined by measuring the variation in longitudinal and transverse magnetizations during magnetic field sweeping. The results suggest that at t Fe = 1 and 3 nm, the reversal occurs cooperatively in a single direction. As t Fe is increased to 5 and 8 nm, the moments switch randomly, in a manner that may be related to the increase in the density of the domain wall, observed by MFM. This work demonstrates the feasibility of reducing coercivity through exchange-spring mechanism and provides information on detailed magnetic reversal mechanism in perpendicular exchange coupled FePt.

SH3 Domains of Grb2 Adaptor Bind to PXψPXR Motifs Within the Sos1 Nucleotide Exchange Factor in a Discriminate Manner

Ubiquitously encountered in a wide variety of cellular processes, the Grb2-Sos1 interaction is mediated through the combinatorial binding of nSH3 and cSH3 domains of Grb2 to various sites containing PXpsiPXR motifs within Sos1. Here, using isothermal titration calorimetry, we demonstrate that while the nSH3 domain binds with affinities in the physiological range to all four sites containing PXpsiPXR motifs, designated S1, S2, S3, and S4, the cSH3 domain can only do so at the S1 site. Further scrutiny of these sites yields rationale for the recognition of various PXpsiPXR motifs by the SH3 domains in a discriminate manner. Unlike the PXpsiPXR motifs at S2, S3, and S4 sites, the PXpsiPXR motif at the S1 site is flanked at its C-terminus with two additional arginine residues that are absolutely required for high-affinity binding of the cSH3 domain. In striking contrast, these two additional arginine residues augment the binding of the nSH3 domain to the S1 site, but their role is not critical for the recognition of S2, S3, and S4 sites. Site-directed mutagenesis suggests that the two additional arginine residues flanking the PXpsiPXR motif at the S1 site contribute to free energy of binding via the formation of salt bridges with specific acidic residues in SH3 domains. Molecular modeling is employed to project these novel findings into the 3D structures of SH3 domains in complex with a peptide containing the PXpsiPXR motif and flanking arginine residues at the S1 site. Taken together, this study furthers our understanding of the assembly of a key signaling complex central to cellular machinery.

Structural basis for recruitment of CBP/p300 coactivators by STAT1 and STAT2 transactivation domains

CBP/p300 transcriptional coactivators mediate gene expression by integrating cellular signals through interactions with multiple transcription factors. To elucidate the molecular and structural basis for CBP-dependent gene expression, we determined structures of the CBP TAZ1 and TAZ2 domains in complex with the transactivation domains (TADs) of signal transducer and activator of transcription 2 (STAT2) and STAT1, respectively. Despite the topological similarity of the TAZ1 and TAZ2 domains, subtle differences in helix packing and surface grooves constitute major determinants of target selectivity. Our results suggest that TAZ1 preferentially binds long TADs capable of contacting multiple surface grooves simultaneously, whereas smaller TADs that are restricted to a single contiguous binding surface form complexes with TAZ2. Complex formation for both STAT TADs involves coupled folding and binding, driven by intermolecular hydrophobic and electrostatic interactions. Phosphorylation of S727, required for maximal transcriptional activity of STAT1, does not enhance binding to any of the CBP domains. Because the different STAT TADs recognize different regions of CBP/p300, there is a potential for multivalent binding by STAT heterodimers that could enhance the recruitment of the coactivators to promoters.

Microstructure and tetragonal-to-orthorhombic phase transition ofAFe2As2(A=Sr,Ca)as seen via transmission electron microscopy

The structural properties of the SrFe2As2 and CaFe2As2 compounds have been extensively analyzed by transmission electron microscopy (TEM) from room temperature down to 20K. The experimental results demonstrate that the SrFe2As2 crystal, in consistence with previous x-ray data, has a tetragonal structure at room temperature and undergoes a tetragonal (T)-orthorhombic (O) phase transition at about 210K. Moreover, twinning lamella arising from T-O transition evidently appears in the orthorhombic phase. On the other hand, TEM observations of CaFe2As2 reveal the presence of a pseudo-periodic structural modulation with the periodicity of around 40nm at room temperature. This modulation is likely in connection with the local structural distortions within the Ca layer. In-situ cooling TEM observations of CaFe2As2 reveal the presence of complex domain structures in the low-temperature orthorhombic phase.

Domain Engineering for Enhanced Ferroelectric Properties of Epitaxial (001) BiFeO Thin Films

Adv. Mater. 2009, 21, 817–823 2009 WILEY-VCH Verlag Gm Multiferroic BiFeO3 has attracted great interest due to its promising application tomagnetoelectric devices. In addition, the high remanent polarization and piezoelectric response of BiFeO3 thin films, which are comparable to those of conventional Ti-rich lead zirconia titanate, suggested BiFeO3 as a strong candidate for lead-free nonvolatile memories. BiFeO3 has a rhombohedral perovskite structure with pseudocubic lattice parameters ar1⁄4 3.96 A and ar1⁄4 0.68. Due to this low symmetry, (001)-oriented epitaxial BiFeO3 films possess the rhombohedral distortion along one of the four (111) crystallographic directions of the pseudocubic perovskite unit cell. Thus, eight possible polarization (ferroelectric) variants, which correspond to four structural (ferroelastic) domains, may form in the films, leading to complex domain patterns with both {100} and {101} twin boundaries. Such a complex domain structure can deteriorate the ferroelectric response of the system by external electric field, and complicates the examination of the coupling between magnetic and ferroelectric order parameters in BiFeO3. [3]

TheAedes aegyptilarval transcriptome: a comparative perspective with emphasis on trypsins and the domain structure of peritrophins

The genome sequence of Aedes aegypti was recently reported. A significant amount of Expressed Sequence Tags (ESTs) were sequenced to aid in the gene prediction process. In the present work we describe an integrated analysis of the genomic and EST data, focusing on genes with preferential expression in larvae (LG), adults (AG) and in both stages (SG). A total of 913 genes (5.4% of the transcript complement) are LG, including ion transporters and cuticle proteins that are important for ion homeostasis and defense. From a starting set of 245 genes encoding the trypsin domain, we identified 66 putative LG, AG, and SG trypsins by manual curation. Phylogenetic analyses showed that AG trypsins are divergent from their larval counterparts (LG), grouping with blood-induced trypsins from Anopheles gambiae and Simulium vittatum. These results support the hypothesis that blood-feeding arose only once, in the ancestral Culicomorpha. Peritrophins are proteins that interlock chitin fibrils to form the peritrophic membrane (PM) that compartmentalizes the food in the midgut. These proteins are recognized by having chitin-binding domains with 6 conserved Cys and may also present mucin-like domains (regions expected to be highly O-glycosylated). PM may be formed by a ring of cells (type 2, seen in Ae. aegypti larvae and Drosophila melanogaster) or by most midgut cells (type 1, found in Ae. aegypti adult and Tribolium castaneum). LG and D. melanogaster peritrophins have more complex domain structures than AG and T. castaneum peritrophins. Furthermore, mucin-like domains of peritrophins from T. castaneum (feeding on rough food) are lengthier than those of adult Ae. aegypti (blood-feeding). This suggests, for the first time, that type 1 and type 2 PM may have variable molecular architectures determined by different peritrophins and/or ancillary proteins, which may be partly modulated by diet.

Determination Factors of Strain-relaxed Complex Domain Structure observed in Thick Epitaxial pb(Zr,Ti)O3Films

AbstractCrystal structure change with the temperature was investigated for 3 m-thick (100)/(001)-oriented epitaxial PbTiO3 films grown on SrTiO3 substrates. Complex strain-relaxed domain structure labeled as Type III was observed and directly transformed to the cubic phase at about 490°C. This transition temperature and the lattice parameter (a and c- axes) change with the temperature well agreed with the reported data for the PbTiO3 powders. The volume fraction of the (001) orientations, Vc, was almost independent of the temperature up to the phase transition temperature. The tilting angles of the spots in XRD plan view were almost the same with the estimated ones from the lattice parameters and the Vc. This suggests that the angle of the domains identified by the domain structure in Type III. This structure is mainly determined by the tetragonality, (c/a ratio) and the Vc.

Transition in Domain Morphology of Block Copolymers Undergoing Polymerization

We have studied the dynamics of a morphology transition of domains in a reactive system composed of A−B block copolymer and B monomer, where polymerization occurs at the end of the B subchain of the block copolymer. We propose a new dynamical model for reactive phase separation, where the chain architecture, the chain conformation, and the spatial distribution of the reaction points (reactive chain ends) are taken into account by the use of random phase approximation. Our model is essentially equivalent to the dynamical self-consistent field theory if the system is close to the critical point, but it has an enormous improvement in the computational efficiency. Simulation results show that our modeling is quite useful partially because the inhomogeneity of the spatial distribution of the reactants affects the polymerization and partially because we can perform large-scale and long time simulations because of the high efficiency of our model. We found that as a result of the competition between the phase separation and the polymerization the system shows complex nonequilibrium domain structures that depend on the kinetic pathway of the phase separation and the polymerization.

Experimental evidence of strain relaxed domain structure in (100)/(001)-oriented epitaxial lead titanate thick films grown by metal organic chemical vapor deposition

Epitaxial (100)/(001)-oriented PbTiO3 films with thickness of 2.8 μm were grown on Nb-doped (100) SrTiO3 substrates by pulsed metal organic chemical vapor deposition. Complex domain structures consisting of c-domains (c1) and three types of a-domains (a1, a2, and a3) were observed by piezoresponse force microscopy in conjunction with high-resolution x-ray diffraction analysis. The obtained results suggest that (a2/a3) and (a1/c1) domain configurations represent mostly strain-relaxed structures. This conclusion is in good agreement with theoretical predictions made for thick films [Phys. State., Solidi 37, 329 (1976)].

A desirable wind up

Multiferroic materials have complex domain structures that make precise interpretation of their behaviours difficult. The creation and study of a single-domain multiferroic crystal is thus an exciting development.

Structural aspects of fast copper mobility in Cu 6PS 5Cl—The best solid electrolyte from [formula omitted] series

The structural origin of fast copper conduction in Cu 6PS 5Cl single crystals is discussed. Cu 6PS 5Cl crystallises in the same cubic F 4 ¯ 3 m symmetry as the other Cu 6PS 5 X's, X = Cl , I , Br . However, this phase is stabilised at much lower temperatures (down to 160 K) and is characterised by higher level of disorder in copper substructure. Complex domain structure developing at low temperatures proves that Cu 6PS 5Cl undergoes ferroelastic phase transition (PT) associated with cubic F 4 ¯ 3 m to monoclinic Cc symmetry change. The structural distortion connected with this transformation is very subtle. X-ray diffraction measurements show strong precursor phenomena below 205 K which correspond to the low temperature phase and point out to copper ordering in nano- or microscopic scale above the temperature of ferroelastic phase transition (PT). The pseudopotential based on copper joint probability density function is calculated along diffusion paths at 175 and 435 K.

Study of the low-temperature behavior of a disordered antiferromagnet with random fields by the parallel-tempering method

The parallel-tempering method has been applied to numerically study the thermodynamic behavior of a three-dimensional disordered antiferromagnetic Ising model with random fields at spin concentrations corresponding to regions of both weak and strong structural disorder. An analysis of the low-temperature behavior of the model convincingly shows that in the case of a weakly disordered samples there is realized an antiferromagnetic ordered state, while in the region of strong structural disorder the effects of random magnetic fields lead to the realization of a new phase state of the system with a complex domain structure consisting of antiferromagnetic and ferromagnetic domains separated by regions of a spin-glass phase and characterized by a spinglass ground state.

Complex domain structure in a magnetic film with oblique anisotropy

Analytical formulas have been derived to calculate the distortion of the stripe domain structure in a ferromagnetic film under the action of a bubble domain formed in this film. On the basis of the formulas obtained, an experimentally obtained domain configuration has been calculated. The results of the calculation coincide with the observation data within the experimental error.

Heme Coordination by Staphylococcus aureus IsdE

Staphylococcus aureus is a Gram-positive bacterial pathogen and a leading cause of hospital acquired infections. Because the free iron concentration in the human body is too low to support growth, S. aureus must acquire iron from host sources. Heme iron is the most prevalent iron reservoir in the human body and a predominant source of iron for S. aureus. The iron-regulated surface determinant (Isd) system removes heme from host heme proteins and transfers it to IsdE, the cognate substrate-binding lipoprotein of an ATP-binding cassette transporter, for import and subsequent degradation. Herein, we report the crystal structure of the soluble portion of the IsdE lipoprotein in complex with heme. The structure reveals a bi-lobed topology formed by an N- and C-terminal domain bridged by a single alpha-helix. The structure places IsdE as a member of the helical backbone metal receptor superfamily. A six-coordinate heme molecule is bound in the groove established at the domain interface, and the heme iron is coordinated in a novel fashion for heme transporters by Met(78) and His(229). Both heme propionate groups are secured by H-bonds to IsdE main chain and side chain groups. Of these residues, His(229) is essential for IsdE-mediated heme uptake by S. aureus when growth on heme as a sole iron source is measured. Multiple sequence alignments of homologues from several other Gram-positive bacteria, including the human pathogens pyogenes, Bacillus anthracis, and Listeria monocytogenes, suggest that these other systems function equivalently to S. aureus IsdE with respect to heme binding and transport.

Structural characteristics of [formula omitted] precipitates in Mg–Zn-based alloys

β 1 ′ precipitates in an Mg 97 Zn 2.5 Y 0.5 alloy are shown to have a complex domain structure based on the structure of monoclinic Mg 4 Zn 7 phase. All domains are oriented with [0 1 0]∥[0 0 0 1] Mg and one of the four planar matches with the matrix. Two of these orientations are related to two others by twinning on the (0 0 1) plane of the Mg 4 Zn 7 phase. These orientations are brought about by crystallographic constraints from the matrix. An ordering of the domains creates a new structure.