Biomedical subjects

Fuyuki Tokumasu

Publications and source records attributed to Fuyuki Tokumasu.

5 recordsLinked to original sources

PubMed2005

Band 3 modifications in Plasmodium falciparum-infected AA and CC erythrocytes assayed by autocorrelation analysis using quantum dots.

The molecular stability of hemoglobin is critical for normal erythrocyte functions, including oxygen transport. Hemoglobin C (HbC) is a mutant hemoglobin that has increased oxidative susceptibility due to an amino acid substitution (beta6: Glu to Lys). The growth of Plasmodium falciparum is abnormal in homozygous CC erythrocytes in vitro, and CC individuals show innate protection against severe P. falciparum malaria. We investigated one possible mechanism of innate protection using a quantum dot technique to compare the distribution of host membrane band 3 molecules in genotypically normal (AA) to CC erythrocytes. The high photostability of quantum dots facilitated the construction of 3D cell images and the quantification of fluorescent signal intensity. Power spectra and 1D autocorrelation analyses showed band 3 clusters on the surface of infected AA and CC erythrocytes. These clusters became larger as the parasites matured and were more abundant in CC erythrocytes. Further, average cluster size (500 nm) in uninfected (native) CC erythrocytes was comparable with that of parasitized AA erythrocytes but was significantly larger (1 microm) in parasitized CC erythrocytes. Increased band 3 clustering may enhance recognition sites for autoantibodies, which could contribute to the protective effect of hemoglobin C against malaria.

Animals↗

PubMed2004

Heterogeneous molecular distribution in supported multicomponent lipid bilayers.

Membrane domains contribute important structural and functional attributes to biological membranes. We describe the heterogeneous nanoscale distribution of lipid molecules within microscale membrane domains in multicomponent lipid bilayers composed of dipalmitoylphosphatidylcholine (DPPC), dilauroylphosphatidylcholine (DLPC), and cholesterol (chol). The lipids were labeled with the fluorescent lipid analogues Bodipy-PC and DiI-C20:0 to identify the distribution of individual membrane components. We used a near-field scanning optical microscope (NSOM) at room temperature to identify the nanoscale structures in the membrane. Simultaneous multicolor NSOM imaging at the emission maxima of the fluorescent analogues revealed a patchy distribution of Bodipy-PC and DiI-C20:0 indicative of phase separations in the bilayer. In a cholesterol-free system (DPPC/DLPC = 1:1), NSOM images proved that the two phosphatidylcholine molecules can coexist in domains at the micrometer level but form nanoscopic patches within the domains; DPPC occurs at the edge of the domains, whereas DLPC is present throughout the domains. In the presence of cholesterol (DPPC/DLPC = 7:3, chol = 18.9%), the two lipid molecules were more miscible but incomplete phase separations also occurred. The average domain sizes were 140-200 nm, well below the resolution capabilities of diffraction-limited light microscopy techniques; the domains were unresolvable by confocal microscopy. Our high-resolution NSOM studies of membrane domain behavior provide a better understanding of complex membrane phase phenomena in multicomponent biological membranes.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2003

Nanoscopic lipid domain dynamics revealed by atomic force microscopy.

Intrinsic heterogeneities, represented as domain formations in biological membranes, are important to both the structure and function of the membranes. We observed domain formations in mixed lipid bilayers of dipalmitoylphosphatidylcholine (DPPC), dilauroylphosphatidylcholine (DLPC), and cholesterol (chol) in a fluid environment using an atomic force microscope (AFM). At room temperature, we demonstrated that both microscopic and nanoscopic domains coexist and the DPPC-rich domain is approximately 1.4 nm higher than the surrounding DLPC-rich membrane areas as a consequence of intrinsic phase differences. DPPC-rich microscopic domains became larger as DPPC concentration increased. In cholesterol-free mixtures, nanoscopic DPPC-rich domain sizes ranged from 26 to 46 nm depending on phospholipid concentration. Domain size varied between 33 and 48 nm in the presence of cholesterol (0 < or = [chol] < or = 40). The nanoscopic domains were markedly fragmented near [chol] = 0.135 and appeared to fuse more readily into microscopic domains at higher and lower [chol]. By phase balance analyses we demonstrated phase behavior differences between a free-vesicle GUV system studied by confocal light microscopy and a supported membrane system studied by AFM. We propose a new three-dimensional phase diagram elucidating the effects of a solid substrate support on lipid phase behavior relevant to complex membrane phase phenomena in biological systems.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2002

Lipid membrane phase behaviour elucidated in real time by controlled environment atomic force microscopy.

Lipids are integral components of all biological membranes. Understanding the physical and chemical properties of these lipids is critical to our understanding of membrane functions. We developed a new atomic force microscope (AFM) approach to visualize in real time the temperature-induced lipid phase transition and domain separation processes in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) membranes and estimate the thermodynamics of the phase transition process. The gel and liquid crystalline phases of DMPC coexisted over a broad temperature range (approximately 10 degrees C). Equal partitioning into two phases occurred at a transition temperature (Tm) of 28.5 degrees C. We developed a mathematical model to analyse AFM-derived DMPC membrane height changes as multi-peak Gaussian distributions. This approach allowed us to estimate the DMPC domain size, N, as 18-75 molecules per leaflet corresponding to a -4.2 nm diameter circular nanodomain. Lipid nanodomains may organize into microdomains or rafts which, in concert with proteins and other lipid components, play an important dynamic role in many biomedically important processes.

Dimyristoylphosphatidylcholine↗

PubMedDate not supplied

Atomic force microscopy of nanometric liposome adsorption and nanoscopic membrane domain formation.

Scanning probe microscopy studies of membrane fusion and nanoscopic structures were performed using hydrated single lipids and lipid mixtures. Extruded vesicles of DMPC and mixtures at various concentrations of DLPC, DPPC and cholesterol were deposited on freshly cleaved mica and studied in a fluid environment by AFM. The nanostructures formed by these extruded liposomes ranged from isolated unilamellar vesicles to flat sheet membranes and were marked influenced by thermodynamic phase behavior. For DMPC membrane, intact bilayers exhibited a phase transition process in agreement with large bilayer patches. In the DLPC, DPPC and cholesterol mixtures, nanoscopic domain diameters ranged from approximately 25 to 48nm with height differences of approximately 1.4nm; all values were lipid composition-dependent. Our data support and extend previous studies of microscopic domains and phase boundaries of the same mixtures in giant unilamellar vesicles determined by confocal light microscopy. Our approach for preparing and utilizing supported membrane structures is potentially relevant to studies of native cell membranes.

Adsorption↗