scholarly journals Protein diffusion on membrane domes, tubes and pearling structures

2020 ◽  
Author(s):  
R. Rojas Molina ◽  
S. Liese ◽  
A. Carlson
Keyword(s):  
Diffusion Time ◽  
Simple Relationship ◽  
Half Time ◽  
Protein Diffusion ◽  
Protein Distribution ◽  
Membrane Morphology ◽  
Complex Shapes ◽  
Membrane Geometry ◽  
Shape Complexity ◽  
Membrane Shape

AbstractDiffusion is a fundamental mechanism for protein distribution in cell membranes. These membranes often exhibit complex shapes, which range from shallow domes to elongated tubular or pearl-like structures. Shape complexity of the membrane influences the diffusive spreading of proteins and molecules. Despite the importance membrane geometry plays in these diffusive processes, it is challenging to establish the dependence between diffusion and membrane morphology. We solve the diffusion equation numerically on various curved shapes representative for experimentally observed membrane shapes. Our results show that membrane necks become diffusion barriers. We determine the diffusive half time, i.e., the time that is required to reduce the amount of proteins in the budded region by one half and find a quadratic relation between the diffusive half time and the averaged mean curvature of the membrane shape. Our findings thus help to estimate the characteristic diffusive time scale based on the simple measure for membrane morphology.Significance statementDiffusion is an integral process for distributing proteins throughout biological membranes. These membranes can have complex shapes and structures, often featuring elongated shapes such as tubes and like a necklace of pearls. The diffusion process on these shapes is significantly different from the well studied planar substrate. We use numerical simulations to understand how the characteristic diffusion time is a function of membrane shape, where we find the diffusion of proteins on strongly curved shapes is significantly slower than on planar membranes. Our results provide a simple relationship to estimate the characteristic diffusion time of proteins on membranes based on its mean and Gaussian curvature.

scholarly journals Curvature-driven feedback on aggregation-diffusion of proteins in lipid bilayers

2021 ◽  
Author(s):  
Arijit Mahapatra ◽  
David Saintillan ◽  
Padmini Rangamani
Keyword(s):  
Lipid Bilayers ◽  
Protein Interactions ◽  
Cell Biology ◽  
Protein Diffusion ◽  
Protein Distribution ◽  
Plane Flow ◽  
Out Of Plane ◽  
Membrane Bending ◽  
Curvature Driven ◽  
And Diffusion

AbstractMembrane bending is an extensively studied problem from both modeling and experimental perspectives because of the wide implications of curvature generation in cell biology. Many of the curvature generating aspects in membranes can be attributed to interactions between proteins and membranes. These interactions include protein diffusion and formation of aggregates due to protein-protein interactions in the plane of the membrane. Recently, we developed a model that couples the in-plane flow of lipids and diffusion of proteins with the out-of-plane bending of the membrane. Building on this work, here, we focus on the role of explicit aggregation of proteins on the surface of the membrane in the presence of membrane bending and diffusion. We develop a comprehensive framework that includes lipid flow, membrane bending energy, the entropy of protein distribution, and an explicit aggregation potential and derive the governing equations. We compare this framework to the Cahn-Hillard formalism to predict the regimes in which the proteins form patterns on the membrane. We demonstrate the utility of this model using numerical simulations to predict how aggregation and diffusion, coupled with curvature generation, can alter the landscape of membrane-protein interactions.

scholarly journals The evolution of bacterial shape complexity by a curvature-inducing module

2020 ◽  
Author(s):  
Nicholas R. Martin ◽  
Edith Blackman ◽  
Benjamin P. Bratton ◽  
Thomas M. Bartlett ◽  
Zemer Gitai
Keyword(s):  
Vibrio Cholerae ◽  
Cell Shape ◽  
Native Species ◽  
Morphological Complexity ◽  
The Core ◽  
Complex Shapes ◽  
Cell Shapes ◽  
Shape Complexity

AbstractBacteria can achieve a staggering diversity of cell shapes that promote critical functions like growth, motility, and virulence1-4. Previous studies suggested that bacteria establish complex shapes by co-opting the core machineries essential for elongation and division5,6. In contrast, we discovered a two-protein module, CrvAB, that can curve bacteria autonomously of the major elongation and division machinery by forming a dynamic, asymmetrically-localized structure in the periplasm. CrvAB is essential for curvature in its native species, Vibrio cholerae, and is sufficient to curve multiple heterologous species spanning 2.5 billion years of evolution. Thus, modular shape determinants can promote the evolution of morphological complexity independently of existing cell shape regulation.

Head-Raising Method of Snake Robots Based on the Bézier Curve

Robotica ◽  
2020 ◽  
pp. 1-21
Author(s):  
Yunhu Zhou ◽  
Yuanfei Zhang ◽  
Fenglei Ni ◽  
Hong Liu
Keyword(s):  
Control Strategy ◽  
Bézier Curve ◽  
Bezier Curve ◽  
Discretization Method ◽  
Backbone Curve ◽  
Degree Elevation ◽  
Snake Robot ◽  
Complex Shapes ◽  
Shape Complexity ◽  
Snake Robots

SUMMARY For acquiring a broad view in an unknown environment, we proposed a control strategy based on the Bézier curve for the snake robot raising its head. Then, an improved discretization method was developed to accommodate the backbone curves with more complex shapes. Besides, in order to determine the condition of using the improved discretization method, energy of framed space curve is introduced originally to estimate the shape complexity of the backbone curve. At last, based on degree elevation of the Bézier curve, an obstacle avoidance strategy of the head-raising motion was proposed and validated through simulation.

Phenomenological model relating cell shape to water reabsorption in proximal nephron

1978 ◽  
Vol 234 (4) ◽  
pp. F308-F317 ◽  
Author(s):  
D. J. Welling ◽  
L. W. Welling ◽  
J. J. Hill
Keyword(s):  
Proximal Tubule ◽  
Phenomenological Model ◽  
Cell Shape ◽  
Serum Proteins ◽  
Water Movement ◽  
Diffusion Constant ◽  
Simple Relationship ◽  
Protein Diffusion ◽  
Flow Parameters ◽  
Morphologic Data

If the complex pattern of intercellular channels in proximal tubule is determined in part by the forces of large transepithelial water flow, the shape of the cells is an indicator of the type and magnitude of the forces required for water movement and the routes of that flow. To test this thesis, morphologic data and volume flow parameters for rabbit proximal tubule are related generally by a mass balance equation. If the intercellular boundaries are assumed to be highly deformable and to respond to changes in hydrostatic pressure, the solution to that equation is a simple relationship between cell shape and the forces required for water movement. The resulting phenomenological model suggests an important new role for peritubular serum proteins and can be used to compute reasonable values for cell wall hydraulic conductivity, intercellular protein diffusion constant, and a channel fluid osmolality not more than 1% greater than that of luminal fluid. It is concluded that quantitative morphologic studies may serve as a powerful means for evaluating and understanding transport phenomena in the nephron.

scholarly journals Unraveling nanotopography of cell surface receptors

2019 ◽  
Author(s):  
Christian Franke ◽  
Tomas Chum ◽  
Zuzana Kvicalova ◽  
Daniela Glatzova ◽  
Alvaro Rodriguez ◽  
...  
Keyword(s):  
Cell Surface ◽  
Single Molecule ◽  
Plasma Membranes ◽  
Immobilized Cells ◽  
Complex Surface ◽  
Protein Distribution ◽  
Detection Scheme ◽  
Surface Receptors ◽  
Membrane Morphology ◽  
Simplified Algorithm

Cells communicate with their environment via surface receptors, but nanoscopic receptor organization with respect to complex cell surface morphology remains unclear. This is mainly due to a lack of accessible, robust and high-resolution methods. Here, we present an approach for mapping the topography of receptors at the cell surface with nanometer precision. The method involves coating glass coverslips with glycine, which preserves the fine membrane morphology while allowing immobilized cells to be positioned close to the optical surface. We developed an advanced and simplified algorithm for the analysis of single-molecule localization data acquired in a biplane detection scheme. These advancements enable direct and quantitative mapping of protein distribution on ruffled plasma membranes with near isotropic 3D nanometer resolution. As demonstrated successfully for CD4 and CD45 receptors, the described workflow is a straightforward quantitative technique to study molecules and their interactions at the complex surface nanomorphology of differentiated metazoan cells.

scholarly journals Membrane Shape Modulates Transmembrane Protein Distribution

2014 ◽  
Vol 28 (2) ◽  
pp. 212-218 ◽  
Author(s):  
Sophie Aimon ◽  
Andrew Callan-Jones ◽  
Alice Berthaud ◽  
Mathieu Pinot ◽  
Gilman E.S. Toombes ◽  
...  
Keyword(s):  
Transmembrane Protein ◽  
Protein Distribution ◽  
Membrane Shape

Meridional Circulation, Turbulence, and Diffusion Processes in Stars

1976 ◽  
Vol 32 ◽  
pp. 109-116 ◽  
Author(s):  
S. Vauclair
Keyword(s):  
Convection Zone ◽  
Diffusion Processes ◽  
Meridional Circulation ◽  
Diffusion Time ◽  
Work In Progress ◽  
First Results ◽  
Stellar Envelopes ◽  
And Diffusion ◽  
Turbulence And Diffusion ◽  
Hr Diagram

This paper gives the first results of a work in progress, in collaboration with G. Michaud and G. Vauclair. It is a first attempt to compute the effects of meridional circulation and turbulence on diffusion processes in stellar envelopes. Computations have been made for a 2 Mʘstar, which lies in the Am - δ Scuti region of the HR diagram.Let us recall that in Am stars diffusion cannot occur between the two outer convection zones, contrary to what was assumed by Watson (1970, 1971) and Smith (1971), since they are linked by overshooting (Latour, 1972; Toomre et al., 1975). But diffusion may occur at the bottom of the second convection zone. According to Vauclair et al. (1974), the second convection zone, due to He II ionization, disappears after a time equal to the helium diffusion time, and then diffusion may happen at the bottom of the first convection zone, so that the arguments by Watson and Smith are preserved.

Transmission Electron Diffraction Analysis by Computer

1970 ◽  
Vol 28 ◽  
pp. 40-41
Author(s):  
R.A. Ploc ◽  
G.H. Keech
Keyword(s):  
Electron Diffraction ◽  
Input Data ◽  
Reciprocal Lattice ◽  
Computer Programme ◽  
Transmission Electron Diffraction ◽  
Usual Procedure ◽  
Transmission Electron ◽  
Complex Shapes ◽  
Computer Input ◽  
Diffraction Effects

An unambiguous analysis of transmission electron diffraction effects requires two samplings of the reciprocal lattice (RL). However, extracting definitive information from the patterns is difficult even for a general orthorhombic case. The usual procedure has been to deduce the approximate variables controlling the formation of the patterns from qualitative observations. Our present purpose is to illustrate two applications of a computer programme written for the analysis of transmission, selected area diffraction (SAD) patterns; the studies of RL spot shapes and epitaxy.When a specimen contains fine structure the RL spots become complex shapes with extensions in one or more directions. If the number and directions of these extensions can be estimated from an SAD pattern the exact spot shape can be determined by a series of refinements of the computer input data.

Freeze fracture imaging and computer simulation of liposome structure: Membrane geometry and defects

1983 ◽  
Vol 41 ◽  
pp. 646-647
Author(s):  
Joseph A. Zasadzinski
Keyword(s):  
Liquid Crystalline ◽  
Freeze Fracture ◽  
Continuum Theory ◽  
Closed Surfaces ◽  
Straight Line ◽  
Low Weight ◽  
Concentric Spheres ◽  
Membrane Geometry ◽  
Dupin Cyclides ◽  
Limiting Case

At low weight fractions, many surfactant and biological amphiphiles form dispersions of lamellar liquid crystalline liposomes in water. Amphiphile molecules tend to align themselves in parallel bilayers which are free to bend. Bilayers must form closed surfaces to separate hydrophobic and hydrophilic domains completely. Continuum theory of liquid crystals requires that the constant spacing of bilayer surfaces be maintained except at singularities of no more than line extent. Maxwell demonstrated that only two types of closed surfaces can satisfy this constraint: concentric spheres and Dupin cyclides. Dupin cyclides (Figure 1) are parallel closed surfaces which have a conjugate ellipse (r1) and hyperbola (r2) as singularities in the bilayer spacing. Any straight line drawn from a point on the ellipse to a point on the hyperbola is normal to every surface it intersects (broken lines in Figure 1). A simple example, and limiting case, is a family of concentric tori (Figure 1b).To distinguish between the allowable arrangements, freeze fracture TEM micrographs of representative biological (L-α phosphotidylcholine: L-α PC) and surfactant (sodium heptylnonyl benzenesulfonate: SHBS)liposomes are compared to mathematically derived sections of Dupin cyclides and concentric spheres.

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