Biological membrane | EPFL Graph Search

A biological membrane, biomembrane or cell membrane is a selectively permeable membrane that separates the interior of a cell from the external environment or creates intracellular compartments by serving as a boundary between one part of the cell and another. Biological membranes, in the form of eukaryotic cell membranes, consist of a phospholipid bilayer with embedded, integral and peripheral proteins used in communication and transportation of chemicals and ions. The bulk of lipids in a cell membrane provides a fluid matrix for proteins to rotate and laterally diffuse for physiological functioning. Proteins are adapted to high membrane fluidity environment of the lipid bilayer with the presence of an annular lipid shell, consisting of lipid molecules bound tightly to the surface of integral membrane proteins. The cell membranes are different from the isolating tissues formed by layers of cells, such as mucous membranes, basement membranes, and serous membranes. Composition

Single-molecule motions of oligoarginine transporter conjugates on the plasma membrane of Chinese hamster ovary cells

Hui Wang

To explore the real-time dynamic behavior of molecular transporters of the cell-penetrating-peptide (CPP) type on a biological membrane, single fluorescently labeled oligoarginine conjugates were imaged interacting with the plasma membrane of Chinese hamster ovary (CHO) cells. The diffusional motion on the membrane, characterized by single-molecule diffusion coefficient and residence time (tau R), defined as the time from the initial appearance of a single-molecule spot on the membrane (from the solution) to the time the single molecule disappears from the imaging focal plane, was observed for a fluorophore-labeled octaarginine (a model guanidinium-rich CPP) and compared with the corresponding values observed for a tetraarginine conjugate (negative control), a lipid analogue, and a fluorescently labeled protein conjugate (transferrin-Alexa594) known to enter the cell through endocytosis. Imaging of the oligoarginine conjugates was enabled by the use of a new high-contrast fluorophore in the dicyanomethylenedihydrofuran family, which brightens upon interaction with the membrane at normal oxygen concentrations. Taken as a whole, the motions of the octaarginine conjugate single molecules are highly heterogeneous and cannot be described as Brownian motion with a single diffusion coefficient. The observed behavior is also different from that of lipids, known to penetrate cellular membranes through passive diffusion, conventionally involving lateral diffusion followed by membrane bilayer flip-flop. Furthermore, while the octaarginine conjugate behavior shares some common features with transferrin uptake (endocytotic) processes, the two systems also exhibit dissimilar traits when diffusional motions and residence times of single constructs are compared. Additionally, pretreatment of cells with cytochalasin D, a known actin filament disruptor, produces no significant effect, which further rules out unimodal endocytosis as the mechanism of uptake. Also, the involvement of membrane potential in octaarginine-membrane interaction is supported by significant changes in the motion with high [K(+)] treatment. In sum, this first study of single transporter motion on the membrane of a living cell indicates that the mode by which the octaarginine transporter penetrates the cell membrane appears to either be a multimechanism uptake process or a mechanism different from unimodal passive diffusion or endocytosis.

2008

Monitoring the Cellular Cholesterol Distribution via nanoSIMS Imaging

Mustafa Demir

Cholesterol is a very important lipid, manufactured by all animal cells for their use. About 20-25% of total daily cholesterol production occurs in the liver; other sites that have higher synthesis rate are intestine, adrenal glands and reproductive organs. It is not only produced in the body cells but also it can be obtained from dietary sources as well. Presence of cholesterol is very crucial for animal cells, since it is the building block of cellular membranes provide membrane fluidity over the range of physiological temperatures; within the cell membrane, it also functions to regulate intracellular transport, cell signaling and nerve conduction. Moreover, it is a precursor for synthesis vitamin D and and steroid hormones. Cholesterol is such an important biological molecule for animal cells, yet it has been a real challenge so far, to understand distribution of cholesterol within the biological membranes. In our study, via using 13C labeled cholesterol, we are able to monitor incorporated cholesterol in cellular structures, with the help of combination of Electron Microscopy imaging and nanoSIMS imaging. Our aim in this study is to address a really fundamental question, what is the distribution gradient of cholesterol, through different layers of cellular membranes.

2015

Monitoring the Cellular Cholesterol Distribution via NanoSIMS Imaging

Mustafa Demir

Cholesterol is a very crucial lipid for animal cells, since it is the building block of cellular membranes, control fluidity of membranes, regulate intracellular transport, cell signalling, nerve conduction and serve as a precursor for synthesis of vitamin D and steroid hormones. Cholesterol is such an important biological molecule for animal cells, yet it has been a real challenge so far, to understand distribution of cholesterol within the biological membranes. In our study, using ultra-high resolution ion microprobe (NanoSIMS) imaging enables us to detect incorporated cholesterol in cells, introduced as 13C labeled cholesterol, in nanometer scale. Then, we are able to monitor the localization of detected cholesterol in cellular structures by combining NanoSIMS (Secondary Ion Mass Spectrometry) with electron microscopy. Our aim in this study is to determine level of incorporated cholesterol in cellular membranes, secretion and endocytic systems, by the help of NanoSIMS imaging combined with electron microscopy.

2015

Single-molecule motions of oligoarginine transporter conjugates on the plasma membrane of Chinese hamster ovary cells

Hui Wang

2008