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Biomedical subjects

D Y Sasaki

Publications and source records attributed to D Y Sasaki.

7 recordsLinked to original sources
PubMed2006

Rearrangement of lipid ordered phases upon protein adsorption due to multiple site binding.

This study involves the interactions of proteins with Langmuir monolayers of a metal-chelating lipid, where adsorption is driven by a strong specific interaction between histidines on the proteins and divalent metal ions loaded into the lipid headgroups. A comparison of the structural rearrangement of the lipid film upon adsorption of myoglobin and a synthetic peptide, each of which have multiple histidines, with that upon the adsorption of lysozyme, which has only one histidine, suggests that the lipid rearrangement in the former case is due to the multiplicity of binding sites. The kinetics and manner of rearrangement change with the binding energy and film pressure.

Adsorption↗
PubMed2005

Adsorption of myoglobin to Cu(II)-IDA and Ni(II)-IDA functionalized langmuir monolayers: study of the protein layer structure during the adsorption process by neutron and X-ray reflectivity.

The structure and orientation of adsorbed myoglobin as directed by metal-histidine complexation at the liquid-film interface was studied as a function of time using neutron and X-ray reflectivity (NR and XR, respectively). In this system, adsorption is due to the interaction between iminodiacetate (IDA)-chelated divalent metal ions Ni(II) and Cu(II) and histidine moieties at the outer surface of the protein. Adsorption was examined under conditions of constant area per lipid molecule at an initial pressure of 40 mN/m. Adsorption occurred over a time period of about 15 h, allowing detailed characterization of the layer structure throughout the process. The layer thickness and the in-plane averaged segment volume fraction were obtained at roughly 40 min intervals by NR. The binding constant of histidine with Cu(II)-IDA is known to be about four times greater than that of histidine with Ni(II)-IDA. The difference in interaction energy led to significant differences in the structure of the adsorbed layer. For Cu(II)-IDA, the thickness of the adsorbed layer at low protein coverage was < or = 20 A and the thickness increased almost linearly with increasing coverage to 42 A. For Ni(II)-IDA, the thickness at low coverage was approximately 38 A and increased gradually with coverage to 47 A. The in-plane averaged segment volume fraction of the adsorbed layer independently confirmed a thinner layer at low coverage for Cu(II)-IDA. These structural differences at the early stages are discussed in terms of either different preferred orientations for isolated chains in the two cases or more extensive conformational changes upon adsorption in the case of Cu(II)-IDA. Subphase dilution experiments provided additional insight, indicating that the adsorbed layer was not in equilibrium with the bulk solution even at low coverages for both IDA-chelated metal ions. We conclude that the weight of the evidence favors the interpretation based on more extensive conformational changes upon adsorption to Cu(II)-IDA.

Adsorption↗
PubMed2004

Analysis of myoglobin adsorption to Cu(II)-IDA and Ni(II)-IDA functionalized Langmuir monolayers by grazing incidence neutron and X-ray techniques.

The adsorption of myoglobin to Langmuir monolayers of a metal-chelating lipid in crystalline phase was studied using neutron and X-ray reflectivity (NR and XR) and grazing incidence X-ray diffraction (GIXD). In this system, adsorption is due to the interaction between chelated divalent copper or nickel ions and the histidine moieties at the outer surface of the protein. The binding interaction of histidine with the Ni-IDA complex is known to be much weaker than that with Cu-IDA. Adsorption was examined under conditions of constant surface area with an initial pressure of 40 mN/m. After approximately 12 h little further change in reflectivity was detected, although the surface pressure continued to slowly increase. For chelated Cu2+ ions, the adsorbed layer structure in the final state was examined for bulk myoglobin concentrations of 0.10 and 10 microM. For the case of 10 microM, the final layer thickness was approximately 43 A. This corresponds well to the two thicker dimensions of myoglobin in the native state (44 A x 44 A x 25 A) and so is consistent with an end-on orientation for this disk-shaped protein at high packing density. However, the final average volume fraction of amino acid segments in the layer was 0.55, which is substantially greater than the value of 0.44 calculated for a completed monolayer from the crystal structure. This suggests an alternative interpretation based on denaturation. GIXD was used to follow the effect of protein binding on the crystalline packing of the lipids and to check for crystallinity within the layer of adsorbed myoglobin. Despite the strong adsorption of myoglobin, very little change was observed in the structure of the DSIDA film. There was no direct evidence in the XR or GIXD for peptide insertion into the lipid tail region. Also, no evidence for in-plane crystallinity within the adsorbed layer of myoglobin was observed. For 0.1 microM bulk myoglobin concentration, the average segment volume fraction was only 0.13 and the layer thickness was < or = 25 A. Adsorption of myoglobin to DSIDA-loaded with Ni2+ was examined at bulk concentrations of 10 and 50 microM. At 10 microM myoglobin, the adsorbed amount was comparable to that obtained for adsorption to Cu2+-loaded DSIDA monolayers at 0.1 M. But interestingly, the adsorbed layer thickness was 38 A, substantially greater than that obtained at low coverage with Cu-IDA. This indicates that either there are different preferred orientations for isolated myoglobin molecules adsorbed to Cu-IDA and Ni-IDA monolayer films or else myoglobin denatures to a different extent in the two cases. Either interpretation can be explained by the very different binding energies for individual interactions in the two cases. At 50 microM myoglobin, the thickness and segement volume fraction in the adsorbed layer for Ni-IDA were comparable to the values obtained with Cu-IDA at 10 microM myoglobin.

Adsorption↗
PubMed2002

Biocompatible semiconductor optoelectronics.

We investigate optoelectronic properties of integrated structures comprising semiconductor light-emitting materials for optical probes of microscopic biological systems. Compound semiconductors are nearly ideal light emitters for probing cells and other microorganisms because of their spectral match to the transparency wavelengths of biomolecules. Unfortunately, the chemical composition of these materials is incompatible with the biochemistry of cells and related biofluids. To overcome these limitations, we investigate functionalized semiconductor surfaces and structures to simultaneously enhance light emission and the flow of biological fluids in semiconductor microcavities. We have identified several important materials problems associated with the semiconductor/biosystem interface. One is the biofluid degradation of electroluminescence by ionic diffusion into compound semiconductors. Ions that diffuse into the active region of a semiconductor light emitter can create point defects that degrade the quantum efficiency of the radiative recombination process. In this paper we discuss ways of mitigating these problems using materials design and surface chemistry, and suggest future applications for these materials.

Animals↗
PubMed2001

Self-assembly of mesoscopically ordered chromatic polydiacetylene/silica nanocomposites.

Nature abounds with intricate composite architectures composed of hard and soft materials synergistically intertwined to provide both useful functionality and mechanical integrity. Recent synthetic efforts to mimic such natural designs have focused on nanocomposites, prepared mainly by slow procedures like monomer or polymer infiltration of inorganic nanostructures or sequential deposition. Here we report the self-assembly of conjugated polymer/silica nanocomposite films with hexagonal, cubic or lamellar mesoscopic order using polymerizable amphiphilic diacetylene molecules as both structure-directing agents and monomers. The self-assembly procedure is rapid and incorporates the organic monomers uniformly within a highly ordered, inorganic environment. Polymerization results in polydiacetylene/silica nanocomposites that are optically transparent and mechanically robust. Compared to ordered diacetylene-containing films prepared as Langmuir monolayers or by Langmuir-Blodgett deposition, the nanostructured inorganic host alters the diacetylene polymerization behaviour, and the resulting nanocomposite exhibits unusual chromatic changes in response to thermal, mechanical and chemical stimuli. The inorganic framework serves to protect, stabilize, and orient the polymer, and to mediate its function. The nanocomposite architecture also provides sufficient mechanical integrity to enable integration into devices and microsystems.

Acetylene↗
PubMed2001

Lipid membrane reorganization induced by chemical recognition.

Nanoscale structural reorganization of a lipid bilayer membrane induced by a chemical recognition event has been imaged using in situ atomic force microscopy (AFM). Supported lipid bilayers, composed of distearylphosphatidylcholine (DSPC) and a synthetic lipid functionalized with a Cu(2+) receptor, phase-separate into nanoscale domains that are distinguishable by the 9 A height difference between the two molecules. Upon binding of Cu(2+) the electrostatic nature of the receptor changes, causing a dispersion of the receptor molecules and subsequent shrinking of the structural features defined by the receptors in the membrane. Complete reversibility of the process was demonstrated through the removal of metal ions with EDTA.

Binding Sites↗