Conserved Central Domains Control the Quaternary Structure of Type I and Type II Hsp40 Molecular Chaperones

Hsp40s play an essential role in protein metabolism by regulating the polypeptide binding and release cycle of Hsp70. The Hsp40 family is large and specialized family members direct Hsp70 to perform highly specific tasks. Type I and Type II Hsp40s, such as yeast Ydj1 and Sis1, are homodimers that dictate functions of cytosolic Hsp70, but how they do so is unclear. Type I Hsp40s contain a conserved centrally located Cysteine-rich domain that is replaced by a Glycine and Methionine rich region in Type II Hsp40s, but the mechanism by which these unique domains influence Hsp40 structure and function is unknown. This is the case because high-resolution structures of full-length forms of these Hsp40s have not been solved. To fill this void we built low-resolution models of the quaternary structure of Ydj1 and Sis1 with information obtained from biophysical measurements of protein shape, small angle X-ray scattering and ab initio protein modeling. Low resolution models were also calculated for the chimeric Hsp40s YSY and SYS, in which the central domains of Ydj1 and Sis1 were exchanged. Similar to their human homologs, Ydj1 and Sis1 each has a unique shape with major structural differences apparently being the orientation of the J-domains relative to the long axis of the dimers. Central domain swapping in YSY and SYS correlates with the switched ability of YSY and SYS to perform unique functions of Sis1 and Ydj1, respectively. Models for the mechanism by which the conserved Cysteine-rich domain and Glycine and Methionine rich region confer structural and functional specificity to Type I and Type II Hsp40s are discussed

On the formation and accessibility of gold nanoparticles confined in SBA-15 mesoporous molecular sieve

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Mesoporous molecular sieves containing metal nanoparticles inside their pores have been lately studied as promising oxidation catalysts. Articles usually claim that confined particles are less prone to sintering and metal leaching. Furthermore, the pores limit nanoparticle growth during the process of preparation of the catalyst. In this work, we addressed some questions that are still to be answered, such as: how are the metal nanoparticles formed within the pores? Are these particles accessible to the organic molecules in catalytic reactions? For this purpose, SBA-15 samples containing Au nanoparticles were prepared and characterized. FTIR, TG/MS, XRD and XPS gave some insights on the formation of Au nanoparticles, while N-2 adsorption and SAXS were useful to address the accessibility question. It was observed that Au-SBA-15, in spite of having a pore size distribution similar of that of SBA-15, has a lower pore volume and half of the surface area. SAXS experimental data was interpreted with the aid of a theoretical model, and it was possible to demonstrate that the presence of metal induced changes on the lattice parameter and pore dimensions of SBA-15. The results strongly indicate that the pores were filled. TEM images reveal the presence of very small Au nanoparticles inside the pores of the material, and also larger particles on its external walls. Au-SBA-15 is thus a material that is very dissimilar from its precursor, pure-silica SBA-15, and so its adsorption properties must be carefully evaluated. (c) 2015 Elsevier Inc. All rights reserved.Mesoporous molecular sieves containing metal nanoparticles inside their pores have been lately studied as promising oxidation catalysts. Articles usually claim that confined particles are less prone to sintering and metal leaching. Furthermore, the pores2108693Fundação 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)FAPESP [2011/12521-0, 2013/11298-0

A biophysical study of DNA condensation mediated by histones and protamines

The compaction of long DNA strands into confined spaces such as the nuclei of eukaryotic cells is an essential phenomenon towards the emergence of elaborated forms of life. Histones and protamines are the major nucleoproteins involved in this task participating in the formation of chromatin in somatic and germinative cells, respectively. In addition to a fundamental understanding of critical biological processes, DNA condensation also holds strong potential in biotechnology. Herein, we investigate the mesoscale structure of complexes formed between DNA and histones or protamines. A sophisticated set of biophysical methods encompassing steady-state fluorimetry, small-angle X-ray scattering and infrared nano spectroscopy was used to unveil both the self-assembly and molecular interactions of these complexes. We explored the fluorescence of a molecular rotor, thioflavin T, to investigate the accessibility of ligands in the inter-base environment of DNA strands. AFM-based infrared spectroscopy was used for the first time to probe the vibrational signature of individual DNA/nucleoprotein nano assemblies and disclose secondary-structure features. Our results show that protamines form highly compact structures in which DNA folding hinders access to the inter-base spacing. These assemblies exhibit diversified secondary-structure conformations, with the presence of -sheets stabilizing the packing. In contrast, histone-based complexes are characterized by fibrillar nano assemblies exhibiting larger inter strands separations and access to guest molecules that intercalate between bases. The findings presented here may help the understanding of DNA condensation mediated by these two major nucleoproteins and may assist the optimization of gene vehicles based on these promising nano assemblies.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP, 19/20907-