The Role of Cell Membranes in Cell Traffic

The cell membrane plays an important role in cell traffic because it functions to secrete various molecules. The selective transport system allows the movement of molecules into or out of the cell compartment. By controlling the movement of substances from one compartment to another, membranes exert a strong influence on metabolic pathways. Cell membranes are composed of proteins and lipids with a very important function in maintaining the rhythm of circulation and cell transport. In addition, the cell membrane also plays a role in maintaining the integrity and relationship, and communication of cells.

Estudo do uso de códons nos vírus da Dengue, Zika e Chikungunya com foco em terapia por inibição seletiva de tRNAs contra arboviroses

O vírus da dengue (DENV), o vírus da Zika (ZIKV) e o vírus da chikungunya (CHIKV) são espécies que apresentam relevância clínica para a saúde pública. Porém, ainda não existe um tratamento específico ou vacina disponível para esses arbovírus. Nesse contexto, é fundamental encontrar novos alvos terapêuticos que possam auxiliar estratégias e tratamentos mais eficientes. A metodologia de codon usage tem demonstrado bons resultados para encontrar alvos para terapias que visam inibidores de tradução. Este estudo buscou analisar o uso de códons e o equilíbrio entre a abundância relativa dos RNAs transportadores (tRNAs) para encontrar alvos terapêuticos que irão estimular novas alternativas de tratamento para infecções causadas pelos DENV, ZIKV e CHIKV. Para tanto, foi replicada uma estratégia computacional, assumindo uma terapia hipotética de inibição seletiva de tRNA (Selective Transport RNA Inhibition Therapy - STRIT), onde foi estabelecido um índice de potencial terapêutico (T-score) para encontrar potenciais espécies de tRNA que poderiam ser inibidas seletivamente para atenuar a replicação viral na célula hospedeira. Foram identificados os cinco códons com maior frequência relativa vírus/hospedeiro (mais relevantes para o vírus) nas seis espécies de arbovírus, notando que todos terminam com purinas A ou G. Os códons GGA (Glicina), AGA (Arginina) e ATA (Isoleucina) são relevantes em todos os flavivirus (ZIKV, DENV-1, DENV-2, DENV-3, DENV-4), mas não no alphavirus CHIKV, onde os códons ACG (Treonina) e CCG (Prolina) são os mais relevantes. Posteriormente, selecionando os cinco códons com maiores T-score nas seis espécies virais (30 códons em total) encontramos apenas 11 códons diferentes, todos terminados com A ou G. Agrupados segundo o nucleotídeo na primeira posição do códon estes 11 códons são: (AGA, ACA, ATA, ACG), (GGA, GCA, GTA, GCG), (CTA, CCG) e (TGG). No agrupamento, notamos outro fato intrigante: que 10 dos 11 códons mais bem ranqueados por T-score, terminam com GA, CA, TA ou CG. Nosso método identificou as espécies de tRNA (através da identificação do códon cognato com maior T-score), cuja inibição funcional por qualquer método específico a anticódon, poderia ter potenciais efeitos terapêuticos em células infectadas pelo vírus da Dengue, Zika e Chikungunya causando a inibição da tradução das proteínas do vírus sem ter um efeito deletério na sobrevivência das células hospedeiras durante o período da infeção. A predominância absoluta dos nucleotídeos A e G na terceira posição dos 11 códons com maior T-score, que por sua vez indica uma preferência dos arbovírus por 11 espécies de tRNA com C ou T na primeira posição do anticódon, abre um novo espaço de pesquisa na interação vírus-hospedeiro.

The Selective Transport of Ions in Charged Nanopore with Combined Multi-Physics Fields

The selective transport of ions in nanopores attracts broad interest due to their potential applications in chemical separation, ion filtration, seawater desalination, and energy conversion. The ion selectivity based on the ion dehydration and steric hindrance is still limited by the very similar diameter between different hydrated ions. The selectivity can only separate specific ion species, lacking a general separation effect. Herein, we report the highly ionic selective transport in charged nanopore through the combination of hydraulic pressure and electric field. Based on the coupled Poisson–Nernst–Planck (PNP) and Navier–Stokes (NS) equations, the calculation results suggest that the coupling of hydraulic pressure and electric field can significantly enhance the ion selectivity compared to the results under the single driven force of hydraulic pressure or electric field. Different from the material-property-based ion selective transport, this method endows the general separation effect between different kinds of ions. Through the appropriate combination of hydraulic pressure and electric field, an extremely high selectivity ratio can be achieved. Further in-depth analysis reveals the influence of nanopore diameter, surface charge density and ionic strength on the selectivity ratio. These findings provide a potential route for high-performance ionic selective transport and separation in nanofluidic systems.

Characterizing Binding Interactions That Are Essential for Selective Transport through the Nuclear Pore Complex

Specific macromolecules are rapidly transported across the nuclear envelope via the nuclear pore complex (NPC). The selective transport process is facilitated when nuclear transport receptors (NTRs) weakly and transiently bind to intrinsically disordered constituents of the NPC, FG Nups. These two types of proteins help maintain the selective NPC barrier. To interrogate their binding interactions in vitro, we deployed an NPC barrier mimic. We created the stationary phase by covalently attaching fragments of a yeast FG Nup called Nsp1 to glass coverslips. We used a tunable mobile phase containing NTR, nuclear transport factor 2 (NTF2). In the stationary phase, three main factors affected binding: the number of FG repeats, the charge of fragments, and the fragment density. We also identified three main factors affecting binding in the mobile phase: the avidity of the NTF2 variant for Nsp1, the presence of nonspecific proteins, and the presence of additional NTRs. We used both experimentally determined binding parameters and molecular dynamics simulations of Nsp1FG fragments to create an agent-based model. The results suggest that NTF2 binding is negatively cooperative and dependent on the density of Nsp1FG molecules. Our results demonstrate the strengths of combining experimental and physical modeling approaches to study NPC-mediated transport.

Accurate Determination of Electrical Potential on Ion Exchange Membranes in Reverse Electrodialysis

Reverse electrodialysis is a promising membrane technology to generate energy from controlled mixing of water streams of different salinities. Electrical potentials generate on the ion exchange membranes (IEMs) when selective transport of cations and anions across the membranes driven by concentration difference. The accurate determination of the potentials developed on the IEMs is critical to fairly assess the feasibility of the technology. The Nernst–Planck–Poisson (NPP) equations for IEMs (the membranes with fixed charge) were solved numerically with the boundary updating scheme. The validity of this numerical method was verified by the identical values of Donnan potential obtained with the well-established analytical methods. The suitability and applicability of the classic Teorell–Meyer–Siever (TMS) model were assessed by comparison to the simulation results from the numerical method.

Monolayer graphene membranes for molecular separation in high-temperature harsh organic solvents

The excellent thermal and chemical stability of monolayer graphene makes it an ideal material for separations at high temperatures and in harsh organic solvents. Here, based on understanding of solvent permeation through nanoporous graphene via molecular dynamics simulation, a resistance model was established to guide the design of a defect-tolerant graphene composite membrane consisting of monolayer graphene on a porous supporting substrate. Guided by the model, we experimentally engineered polyimide (PI) supporting substrates with appropriate pore size, permeance, and excellent solvent resistance and investigated transport across the resulting graphene-covered membranes. The cross-linked PI substrate could effectively mitigate the impacts of leakage through defects across graphene to allow selective transport without defect sealing. The graphene-covered membrane showed pure solvent permeance of 24.1 L m−2 h−1 bar−1 and stable rejection (∼90%) of Allura Red AC (496.42 g mol−1) in a harsh polar solvent, dimethylformamide (DMF), at 100 °C for 10 d.