Micro-Raman and micro-transmission imaging of epitaxial graphene grown on the Si and C faces of 6H-SiC

Micro-Raman and micro-transmission imaging experiments have been done on epitaxial graphene grown on the C- and Si-faces of on-axis 6H-SiC substrates. On the C-face it is shown that the SiC sublimation process results in the growth of long and isolated graphene ribbons (up to 600 μm) that are strain-relaxed and lightly p-type doped. In this case, combining the results of micro-Raman spectroscopy with micro-transmission measurements, we were able to ascertain that uniform monolayer ribbons were grown and found also Bernal stacked and misoriented bilayer ribbons. On the Si-face, the situation is completely different. A full graphene coverage of the SiC surface is achieved but anisotropic growth still occurs, because of the step-bunched SiC surface reconstruction. While in the middle of reconstructed terraces thin graphene stacks (up to 5 layers) are grown, thicker graphene stripes appear at step edges. In both the cases, the strong interaction between the graphene layers and the underlying SiC substrate induces a high compressive thermal strain and n-type doping

Properties of Graphene: A Theoretical Perspective

In this review, we provide an in-depth description of the physics of monolayer and bilayer graphene from a theorist's perspective. We discuss the physical properties of graphene in an external magnetic field, reflecting the chiral nature of the quasiparticles near the Dirac point with a Landau level at zero energy. We address the unique integer quantum Hall effects, the role of electron correlations, and the recent observation of the fractional quantum Hall effect in the monolayer graphene. The quantum Hall effect in bilayer graphene is fundamentally different from that of a monolayer, reflecting the unique band structure of this system. The theory of transport in the absence of an external magnetic field is discussed in detail, along with the role of disorder studied in various theoretical models. We highlight the differences and similarities between monolayer and bilayer graphene, and focus on thermodynamic properties such as the compressibility, the plasmon spectra, the weak localization correction, quantum Hall effect, and optical properties. Confinement of electrons in graphene is nontrivial due to Klein tunneling. We review various theoretical and experimental studies of quantum confined structures made from graphene. The band structure of graphene nanoribbons and the role of the sublattice symmetry, edge geometry and the size of the nanoribbon on the electronic and magnetic properties are very active areas of research, and a detailed review of these topics is presented. Also, the effects of substrate interactions, adsorbed atoms, lattice defects and doping on the band structure of finite-sized graphene systems are discussed. We also include a brief description of graphane -- gapped material obtained from graphene by attaching hydrogen atoms to each carbon atom in the lattice.Comment: 189 pages. submitted in Advances in Physic

Human Hsp70/Hsp90 Organizing Protein (Hop) D456G Is a Mixture of Monomeric and Dimeric Species

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Hop is a tetratricopeptide repeat domain (TPR)-containing co-chaperone that is able to directly associate with both Hsp70 and Hsp90. Previous data showed that the TPR2A-domain is the primary site for dimerization and that the TPR2B-domain may also play a role in dimerization. We present Hop-D456G, a mutant within the TPR2B-domain, that is a mixture of monomeric and dimeric species.174492498Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fogarty International Center [NIH-R03TW007437]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fogarty International Center [NIH-R03TW007437

The Stability of Wild-type and Deletion Mutants of Human C-terminus Hsp70-interacting Protein (CHIP)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Carboxyl terminus of Hsp70 interacting protein (CHIP) is a dimeric co-chaperone involved in providing an appropriate balance between the synthesis and degradation of proteins, which is essential for normal cellular growth and function. Previous work has shown that CHIP, but not its isolated domains, has chaperone activity that is enhanced by heat. In this work, we investigate how heat and urea affect the stability of its domains. We found that the deletion mutant containing the TPR domain, which binds to chaperones Hsp70 or Hsp90, was monomeric and showed similar folding and stability to WT, while the mutant containing the U-box ubiquitin ligase domain was dimeric but had very low stability. The deletion mutants appeared to maintain most of their structure compared to the WT protein, but the regions around the tryptophan residues, which are at the interface of the domains in the WT structure, appeared to be more unfolded, which indicated that the region of contact between domains is likely important for the chaperone function.205524529Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Human mitochondrial import receptor Tom70 functions as a monomer

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The mitochondrial import receptor Tom70 (translocase of the mitochondrial outer membrane 70) interacts with chaperone-preprotein complexes through two domains: one that binds Hsp70 (heat-shock protein 70)/Hsc70 (heat-shock cognate 70) and Hsp90, and a second that binds preproteins. The oligomeric state of Tom70 has been controversial, with evidence for both monomeric and homodimeric forms. In the present paper, we report that the functional state of human Tom70 appears to be a monomer with mechanistic implications for its function in mitochondrial protein import. Based on analytical ultracentrifugation, cross-linking, size-exclusion chromatography and multi-angle light scattering, we found that the soluble cytosolic fragment of human Tom70 exists in equilibrium between monomer and dimer. A point mutation introduced at the predicted dimer interface increased the percentage of monomeric Tom70. Although chaperone docking to the mutant was the same as to the wild-type, the mutant was significantly more active in preprotein targeting. Cross-linking also demonstrated that the mutant formed stronger contacts with preprotein. However, cross-linking of full-length wild-type Tom70 on the mitochondrial membrane showed little evidence of homodimers. These results indicate that the Tom70 monomers are the functional form of the receptor, whereas the homodimers appear to be a minor population, and may represent an inactive state.4293553563Canadian Institutes of Health Research [MOP-68825]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Canadian Institutes of Health Research [MOP-68825

Human hnRNP Q re-localizes to cytoplasmic granules upon PMA, thapsigargin, arsenite and heat-shock treatments

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Eukaryotic gene expression is regulated on different levels ranging from pre-mRNA processing to translation. One of the most characterized families of RNA-binding proteins is the group of hnRNPs: heterogenous nuclear ribonucleoproteins. Members of this protein family play important roles in gene expression control and mRNAs metabolism. In the cytoplasm, several hnRNPs proteins are involved in RNA-related processes and they can be frequently found in two specialized structures, known as GW-bodies (GWbs), previously known as processing bodies: PBs, and stress granules, which may be formed in response to specific stimuli. GWbs have been early reported to be involved in the mRNA decay process, acting as a site of mRNA degradation. In a similar way, stress granules (SGs) have been described as cytoplasmic aggregates, which contain accumulated mRNAs in cells under stress conditions and present reduced or inhibited translation. Here, we characterized the hnRNP Q localization after different stress conditions. hnRNP Q is a predominantly nuclear protein that exhibits a modular organization and several RNA-related functions. Our data suggest that the nuclear localization of hnRNP Q might be modified after different treatments, such as: PMA, thapsigargin, arsenite and heat shock. Under different stress conditions, hnRNP Q can fully co-localize with the endoplasmatic reticulum specific chaperone, BiP. However, under stress, this protein only co-localizes partially with the proteins: GW182 - GWbs marker protein and TIA-1 stress granule component. (C) 2009 Elsevier Inc. All rights reserved.3156968980Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)LNLSFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPESP [05/00235-1

DNA and heparin chaperone the refolding of purified recombinant replication protein A subunit 1 from Leishmania amazonensis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Replication protein A (RPA) is a single-stranded DNA-binding protein that has been implicated in DNA metabolism and telomere maintenance. Subunit 1 of RPA from Leishmania amazonensis (LaRPA-1) has previously been affinity-purified oil a column containing a G-rich telomeric DNA. LaRPA-1 binds and co-localizes with parasite telomeres in vivo. Here we describe the purification and characterization of native recombinant LaRPA-1 (rLaRPA-1). The protein was initially re-solubilized from inclusion bodies by using urea. After dialysis, rLaRPA-1 was soluble but contaminated with DNA, which was removed by an anion-exchange chromatography of the protein solubilized ill Urea. However, rLaRPA-1 precipitated after dialysis to remove urea. To investigate whether the contaminating DNA was involved in chaperoning the refolding of rLaRPA-1, salmon sperm DNA or heparin was added to the solution before dialysis. The addition of either of these Substances prevented the precipitation of rLaRPA-1. The resulting rLaRPA-1 was soluble, correctly folded, and able to bind telomeric DNA. This is the first report showing the characterization of rLaRPA1 and of the importance of additives in chaperoning the refolding of this protein. The availability of rLaRPA-1 should be helpful in assessing the importance of this protein as a potential drug target. (C) 2008 Elsevier B.V. All rights reserved.17902119125UNICEF/UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases [ID A50762]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fogarty International Center [NIH-R03TW007437]FAPESRFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)UNICEF/UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases [ID A50762]FAPESP [06/58175-7]Fogarty International Center [NIH-R03TW007437

Structural studies of human purine nucleoside phosphorylase: Towards a new specific empirical scoring function

Human purine nucleoside phosphorylase (HsPNP) is a target for inhibitor development aiming at T-cell immune response modulation. In this work, we report the development of a new set of empirical scoring functions and its application to evaluate binding affinities and docking results. To test these new functions, we solved the structure of HsPNP and 2-mercapto-4(3H)-quinazolinone (HsPNP:MQU) binary complex at 2.7 A resolution using synchrotron radiation, and used these functions to predict ligand position obtained in Clocking Simulations. We also employed molecular dynamics simulations to analyze HsPNP in two conditions, as apoenzyme and in the binary complex form, in order to assess the structural features responsible for stability. Analysis of the Structural differences between systems provides explanation for inhibitor binding. The use of these scoring functions to evaluate binding affinities and molecular docking results may be used to guide future efforts on virtual screening focused on HsPNP. (c) 2008 Elsevier Inc. All rights reserved.4791283