Molecular dynamics simulation of adhesion forces in a dipalmitoylphosphatidylcholine membrane

Adhesion forces of Dipalmitoylphosphatidylcholine ( DPPC) membrane in the gel phase are investigated by molecular dynamics ( MD) simulation. In the simulations, individual DPPC molecules are pulled out of DPPC membranes with different rates and we get the maximum adhesion forces of DPPC membrane. We find that the maximum adhesion forces increase with pull rate, from about 400 to 700 pN when pull rates are from 0.001 to 0.03 nm/ps. We analyze the relationship between pull rate and adhesion forces of different origins using Brownian dynamics and notice that viscosity of solvent plays an important role in adhesion forces. Then we simulate the motion of a single DPPC molecule in solvent and it elucidates that the maximum drag force is almost linear with respect to the pull rate. We use Stokes' relation to describe the motion of a single DPPC molecule and deduce the effective length of a DPPC molecule. Conformational analyses indicate that the free energy variation of a DPPC molecule inside and outside of the DPPC membrane is an essential part of adhesion energy.

Deformation Of Pdms Membrane And Microcantilever By A Water Droplet: Comparison Between Mooney-Rivlin And Linear Elastic Constitutive Models

In this paper, we studied the role of vertical component Of Surface tension of a water droplet on the deformation of membranes and microcantilevers (MCLs) widely used in lab-on-a-chip and micro-and nano-electromechanical system (MEMS/NEMS). Firstly, a membrane made of a rubber-like material, poly(dimethylsiloxane) (PDMS), was considered. The deformation was investigated using the Mooney-Rivlin (MR) model and the linear elastic constitutive relation, respectively. By comparison between the numerical solutions with two different models, we found that the simple linear elastic model is accurate enough to describe such kind of problem, which would be quite convenient for engineering applications. Furthermore, based on small-deflection beam theory, the effect of a liquid droplet on the deflection of a MCL was also studied. The free-end deflection of the MCL was investigated by considering different cases like a cylindrical droplet, a spherical droplet centered on the MCL and a spherical droplet arbitrarily positioned on the MCL. Numerical simulations demonstrated that the deflection might not be neglected, and showed good agreement with our theoretical analyses. (C) 2008 Elsevier Inc. All rights reserved.

Elastic deformation of soft membrane with finite thickness induced by a sessile liquid droplet

In this paper, the role of vertical component of Surface tension of a droplet on the elastic deformation of a finite-thickness flexible membrane was theoretically analyzed using Hankel transformation. The vertical displacement at the Surface was derived and can be reduced to Lester's or Rusanov's solutions when the thickness is infinite. Moreover, some Simulations of the effect of a liquid droplet on a membrane with a finite thickness were made. The numerical results showed that there exists a saturated membrane thickness of the order of millimeter, when the thickness of a membrane is larger than such a value, the membrane can be regarded as a half-infinite body. Further numerical calculations for soft membrane whose thickness is far below the saturated thickness were made. By comparison between the maximum vertical displacement of an ultrathin soft membrane and a half-infinite body, we found that Lester's or Rusanov's solutions for a half-infinite body cannot correctly describe Such cases. In other words, the thickness of a soft membrane has great effect on the surface deformation of the ultrathin membrane induced by a liquid droplet. (C) 2009 Elsevier Inc. All rights reserved.

Membrane Deformability and Membrane Tension of Single Isolated Mitochondria

Mitochondria dynamics is crucial to many biological processes such as mitochondria fusion and fission, which is highly correlated to the mechanics of single mitochondria. However, the mechanobiological coupling of mitochondria has been poorly understood. Here membrane deformability and membrane tension of individual mitochondria isolated from MtDsRed labeled human embryonic T-Rex-293 kidney cells were measured using a micropipette aspiration assay. The results demonstrated that membrane deformation of isolated mitochondria exhibited an elastic transition phase followed by an equilibrium phase, and mitochondrial membrane tension was proportional to the area compressibility. It was also indicated that mitochondrial membrane deformability was significantly affected by physical chemical factors such as osmotic pressure or pH value, and was further correlated to mitochondrial functionality in different respiratory states and Ca2+ regulation. These findings provide a new insight into understanding the mechanical regulation of mitochondrial physiology.

Constitutive plasma membrane targeting and microdomain localization of Dok5 studied by single-molecule microscopy

In the present study, single-molecule fluorescence microscopy was used to examine the characteristics of plasma membrane targeting and microdomain localization of enhanced yellow fluorescent protein (eYFP)-tagged wild-type Dok5 and its variants in living Chinese hamster ovary (CHO) cells. We found that Dok5 can target constitutively to the plasma membrane, and the PH domain is essential for this process. Furthermore, single-molecule trajectories analysis revealed that Dok5 can constitutively partition into microdomain on the plasma membrane. Finally, the potential mechanism of microdomain localization of Dok5 was discussed. This study provided insights into the characteristics of plasma membrane targeting and microdomain localization of Dok5 in living CHO cells. (C) 2008 Elsevier B.V. All rights reserved.

Direct visualization of the dynamics of membrane-anchor proteins in living cells

Dynamic properties of proteins have crucial roles in understanding protein function and molecular mechanism within cells. In this paper, we combined total internal reflection fluorescence microscopy with oblique illumination fluorescence microscopy to observe directly the movement and localization of membrane-anchored green fluorescence proteins in living cells. Total internal reflect illumination allowed the observation of proteins in the cell membrane of living cells since the penetrate depth could be adjusted to about 80 nm, and oblique illumination allowed the observation of proteins both in the cytoplasm and apical membrane, which made this combination a promising tool to investigate the dynamics of proteins through the whole cell. Not only individual protein molecule tracks have been analyzed quantitatively but also cumulative probability distribution function analysis of ensemble trajectories has been done to reveal the mobility of proteins. Finally, single particle tracking has acted as a compensation for single molecule tracking. All the results exhibited green fluorescence protein dynamics within cytoplasm, on the membrane and from cytoplasm to plasma membrane.

Detection of constitutive homomeric associations of the integrins Mac-1 subunits by fluorescence resonance energy transfer in living cells

Integrins alpha(M)beta(2) plays important role on leukocytes, such as adhesion, migration, phagocytosis, and apoptosis. It was hypothesized that homomeric associations of integrin subunits provide a driving force for integrins activation, and simultaneously inducing the formation of integrins clusters. However, experimental reports on homomeric associations between integrin subunits are still controversial. Here, we proved the homomeric associations of the isolated Mac-1 subunits in living cells using three-channel fluorescence resonance energy transfer (FRET) microscopy and FRET spectra methods. We found that the extent of homomeric associations between beta(2) subunits is higher than alpha(M) subunits. Furthermore, FRET imaging indicated that the extent of homomeric associations of the Mac-1 subunits is higher along the plasma membrane than in the cytoplasm. Finally, we suggested that homomeric associations of the transmernbrane domains or/and cytoplasmic domains may provide the driving force for the formation of constitutive homomeric associations between alpha(M) or beta(2) subunits. (c) 2006 Elsevier Inc. All rights reserved.