Thermodynamic competition between membrane protein oligomeric states

Self-assembly of protein monomers into distinct membrane protein oligomers provides a general mechanism for diversity in the molecular architectures, and resulting biological functions, of membrane proteins. We develop a general physical framework describing the thermodynamic competition between different oligomeric states of membrane proteins. Using the mechanosensitive channel of large conductance as a model system, we show how the dominant oligomeric states of membrane proteins emerge from the interplay of protein concentration in the cell membrane, protein-induced lipid bilayer deformations, and direct monomer-monomer interactions. Our results suggest general physical mechanisms and principles underlying regulation of protein function via control of membrane protein oligomeric state.Comment: 7 pages, 5 figure

Controlling the shape of membrane protein polyhedra

Membrane proteins and lipids can self-assemble into membrane protein polyhedral nanoparticles (MPPNs). MPPNs have a closed spherical surface and a polyhedral protein arrangement, and may offer a new route for structure determination of membrane proteins and targeted drug delivery. We develop here a general analytic model of how MPPN self-assembly depends on bilayer-protein interactions and lipid bilayer mechanical properties. We find that the bilayer-protein hydrophobic thickness mismatch is a key molecular control parameter for MPPN shape that can be used to bias MPPN self-assembly towards highly symmetric and uniform MPPN shapes. Our results suggest strategies for optimizing MPPN shape for structural studies of membrane proteins and targeted drug delivery

Dipoles in thin sheets

A flat elastic sheet may contain pointlike conical singularities that carry a metrical "charge" of Gaussian curvature. Adding such elementary defects to a sheet allows one to make many shapes, in a manner broadly analogous to the familiar multipole construction in electrostatics. However, here the underlying field theory is non-linear, and superposition of intrinsic defects is non-trivial as it must respect the immersion of the resulting surface in three dimensions. We consider a "charge-neutral" dipole composed of two conical singularities of opposite sign. Unlike the relatively simple electrostatic case, here there are two distinct stable minima and an infinity of unstable equilibria. We determine the shapes of the minima and evaluate their energies in the thin-sheet regime where bending dominates over stretching. Our predictions are in surprisingly good agreement with experiments on paper sheets.Comment: 20 pages, 5 figures, 2 table

Stochastic single-molecule dynamics of synaptic membrane protein domains

Motivated by single-molecule experiments on synaptic membrane protein domains, we use a stochastic lattice model to study protein reaction and diffusion processes in crowded membranes. We find that the stochastic reaction-diffusion dynamics of synaptic proteins provide a simple physical mechanism for collective fluctuations in synaptic domains, the molecular turnover observed at synaptic domains, key features of the single-molecule trajectories observed for synaptic proteins, and spatially inhomogeneous protein lifetimes at the cell membrane. Our results suggest that central aspects of the single-molecule and collective dynamics observed for membrane protein domains can be understood in terms of stochastic reaction-diffusion processes at the cell membrane.Comment: Main text (7 pages, 4 figures, 1 table) and supplementary material (3 pages, 3 figures

Determination of Flower Characteristics of Some Kiwifruit Genotypes (Actinidia Spp.) Obtained with Breeding Program

All Actinidia species are dioecious, male and female flowers grow on separate kiwifruit plants. In breeding studies, it is generally desirable to obtain female individuals. However, male plants are also of great importance for pollination. Therefore, it is necessary to examine the flower characteristics of the genotypes obtained by breeding studies. This research was conducted in the kiwifruit breeding plot of Yalova Atatürk Horticultural Central Research Institute for two years. Genotypes obtained from cultivars belonging to Actinidia deliciosa and Actinidia chinensis were used in the research. At the time of flowering, phenological observations of male and female genotypes, which are prominent in the population, have been made and the developmental stages of the flowers have been determined. At least 10 flowers of each genotype were used to determine the morphological characteristics.Number of leaves, number of petals, number of male organs, number of filaments, number of female organs, number of female organs and number of stylus were examined in order to determine flower characteristics. When the data obtained as a result of two years are evaluated; significant differences have been obtained particularly in terms of flowering time, flowering period, the number of stylus, the filament size, the number of female organs and the number of male organs. Female cultivars/genotypes tend to flowering later than male cultivars/genotypes, and female cultivars/genotypes have shorter filament length than male cultivars/genotypes. It has also been clearly observed that ovaries are not functional in male types

Eltrombopag for the treatment of immune thrombocytopenia: The aegean region of Turkey experience

Objective: Immune thrombocytopenia (ITP) is an immune-mediated disease characterized by transient or persistent decrease of the platelet count to less than 100x109/L. Although it is included in a benign disease group, bleeding complications may be mortal. With a better understanding of the pathophysiology of the disease, thrombopoietin receptor agonists, which came into use in recent years, seem to be an effective option in the treatment of resistant cases. This study aimed to retrospectively assess the efficacy, long-term safety, and tolerability of eltrombopag in Turkish patients with chronic ITP in the Aegean region of Turkey. Materials and Methods: Retrospective data of 40 patients with refractory ITP who were treated with eltrombopag in the Aegean region were examined and evaluated. Results: The total rate of response was 87%, and the median duration of response defined as the number of the platelets being over 50x109/L was 19.5 (interquartile range: 5-60) days. In one patient, venous sinus thrombosis was observed with no other additional risk factors due to or related to thrombosis. Another patient with complete response and irregular follow-up for 12 months was lost due to sudden death as the result of probable acute myocardial infarction. Conclusion: Although the responses to eltrombopag were satisfactory, patients need to be monitored closely for overshooting platelet counts as well as thromboembolic events. © 2015 Turkish Society of Hematology. All rights reserved