Attachment of Rod-Like (BAR) Proteins and Membrane Shape

Previous studies have shown that cellular function depends on rod-like membrane proteins, among them Bin/Amphiphysin/Rvs (BAR) proteins may curve the membrane leading to physiologically important membrane invaginations and membrane protrusions. The membrane shaping induced by BAR proteins has a major role in various biological processes such as cell motility and cell growth. Different models of binding of BAR domains to the lipid bilayer are described. The binding includes hydrophobic insertion loops and electrostatic interactions between basic amino acids at the concave region of the BAR domain and negatively charged lipids. To shed light on the elusive binding dynamics, a novel experiment is proposed to expand the technique of single-molecule AFM for the traction of binding energy of a single BAR domain

Interaction between macroions mediated by divalent rod-like ions

Attractive interactions between identical like-charged macroions in aqueous multivalent salt solution arise due to ion-ion correlations. The mean-field level Poisson-Boltzmann (PB) theory does not predict such behavior for point-like structureless ions. Various multivalent ions, such as certain DNA condensing agents or short stiff polyelectrolytes, do have an internal, often rod-like, structure. Applying PB theory to the generic case of divalent rod-like salt ions, we find attraction between like-charged macroions above a critical distance between the two individual charges of the rod-like ions. We calculate this distance analytically within linearized PB theory. Numerical results for the non-linear PB theory indicate strong enhancement of the tendency to mediate attractive interactions

Computer Determination of Contact Stress Distribution and Size of Weight Bearing Area in the Human Hip Joint

The mathematical models and the corresponding computer program for determination of the hip joint contact force, the contact stress distribution, and the size of the weight bearing area from a standard anteroposterior radiograph are described. The described method can be applied in clinical practice t

Vesiculation of biological membrane driven by curvature induced frustrations in membrane orientational ordering

Dalija Jesenek,1 Šarká Perutková,2 Wojciech Góźdź,3 Veronika Kralj-Iglič,4 Aleš Iglič,2,5 Samo Kralj1,61Condensed Matter Physics Department, Jožef Stefan Institute, Ljubljana, Slovenia; 2Laboratory of Biophysics, Faculty of Electrical Engineering, University of Ljubljana, Ljubljana, Slovenia; 3Department of Complex Systems and Chemical Processing of Information, Institute of Physical Chemistry, Polish Academy of Sciences, Warsaw, Poland; 4Laboratory of Clinical Biophysics, Faculty of Health Studies, University of Ljubljana, Ljubljana, Slovenia; 5Laboratory of Clinical Biophysics, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia; 6Department of Physics, Faculty of Natural Sciences and Mathematics, University of Maribor, Maribor, SloveniaAbstract: Membrane budding often leads to the formation and release of microvesicles. The latter might play an important role in long distance cell-to-cell communication, owing to their ability to move with body fluids. Several mechanisms exist which might trigger the pinching off of globular buds from the parent membrane (vesiculation). In this paper, we consider the theoretical impacts of topological defects (frustrations) on this process in the membranes that exhibit global in-plane orientational order. A Landau–de Gennes theoretical approach is used in terms of tensor orientational order parameters. The impact of membrane shapes on position and the number of defects is analyzed. In studied cases, only defects with winding numbers m = ±1/2 appear, where we refer to the number of defects with m = 1/2 as defects, and with m = –1/2 as anti-defects. It is demonstrated that defects are attracted to regions with maximal positive Gaussian curvature, K. On the contrary, anti-defects are attracted to membrane regions exhibiting minimal negative values of K. We show on membrane structures exhibiting spherical topology that the coexistence of regions with K > 0 and K < 0 might trigger formation of defect–anti-defect pairs for strong enough local membrane curvatures. Critical conditions for triggering pairs are determined in several demonstrative cases. Then the additionally appeared anti-defects are assembled at the membrane neck, where K < 0. Consequent strong local fluctuations of membrane constituent anisotropic molecules might trigger membrane fission neck rupture, enabling a membrane fission process and the release of membrane daughter microvesicles (ie, vesiculation).Keywords: structural transitions, topological defects, membrane microvesicles, membrane curvature, membrane fission, vesiculatio

Self-assembly of linear aggregates on curved membranes

Recent experiments evidence the strong influence that linear aggregation of beta-sheet peptides can have on the conformation and stability of lipid membranes. We have therefore studied in the dilute limit the self-assembly of one-dimensional aggregates bound to a fluid-like membrane of prescribed curvatures. Each aggregate is characterized by its persistence length and an interaction potential with the membrane. For strong adsorption of flexible aggregates the bending stiffness of the composite membrane grows linearly with the total concentration of aggregate-forming units. For weak adsorption of rigid aggregates the dependence is cubic for which we show —based on a hydrophobic matching hypothesis— that the aggregates can significantly contribute to or even dominate the bending stiffness. We also show how the membrane curvature affects the orientational and size distribution of the aggregates

Normal red blood cells' shape stabilized by membrane's in-plane ordering

Red blood cells (RBCs) are present in almost all vertebrates and their main function is to transport oxygen to the body tissues. RBCs' shape plays a significant role in their functionality. In almost all mammals in normal conditions, RBCs adopt a disk-like (discocyte) shape, which optimizes their flow properties in vessels and capillaries. Experimentally measured values of the reduced volume (v) of stable discocyte shapes range in a relatively broad window between v ~ 0.58 and 0.8. However, these observations are not supported by existing theoretical membrane-shape models, which predict that discocytic RBC shape is stable only in a very narrow interval of v values, ranging between v ~ 0.59 and 0.65. In this study, we demonstrate that this interval is broadened if a membrane's in-plane ordering is taken into account. We model RBC structures by using a hybrid Helfrich-Landau mesoscopic approach. We show that an extrinsic (deviatoric) curvature free energy term stabilizes the RBC discocyte shapes. In particular, we show on symmetry grounds that the role of extrinsic curvature is anomalously increased just below the nematic in-plane order-disorder phase transition temperature

The role of obesity, biomechanical constitution of the pelvis and contact joint stress in progression of hip osteoarthritis

SummaryObjectiveThe aim of our study was to explore whether earlier hip arthroplasty for idiopathic osteoarthritis (OA) might be explained by enlarged contact stress in the hip joint, and to what amount can that be attributed to obesity and biomechanical constitution of the pelvis.MethodFifty subjects were selected from a list of consecutive recipients of hip endoprosthesis due to idiopathic OA; standard pelvic radiographs made years prior to surgery were the main selection criteria. For 65 hips resultant hip force and peak contact hip stress normalized to the body weight (R/Wb and pmax/Wb) were determined from the radiographs with the HIPSTRESS method. Body weight and body mass index (BMI) were obtained with an interview. Regression analysis was used to correlate parameters of obesity (body weight, BMI), biomechanical constitution of the pelvis (R/Wb, pmax/Wb) and mechanical loading within the hip joint (R, pmax) with age at hip arthroplasty.ResultsYounger age at hip arthroplasty was associated with higher body weight (P=0.009), higher peak contact hip stress normalized to the body weight – pmax/Wb (P=0.019), higher resultant hip force – R (P=0.027) and larger peak contact hip stress – pmax (P<0.001), but not with BMI (P=0.121) or R/Wb (P=0.614).ConclusionOur results suggest that enlarged contact stress (pmax) plays an important role in rapid progression of hip OA with both obesity (increased body weight) and unfavorable biomechanical constitution of the pelvis (greater pmax/Wb) contributing