European Biophysics Journal最新文献

In the study of protein self-assembly, knowledge of the extent of electrical and hydrophobic interactions is important. In previous work our group deduced an expression for the hydrophobic energy between the monomers of an assembly. This energy decays exponentially with a characteristic distance r_H. The object of this work is to obtain a more precise physical interpretation of r_H. In very simple systems, according to our model, r_H turns out to be the distance between the hydrophobic dipole moment vectors H. As systems become more complex and the action of the electrostatic dipole moment vectors D appear, discrepancies begin to be seen between the values obtained for r_H and the distances between vectors. It is observed that the simple application of Coulomb’s law is not sufficient to explain these discrepancies. We introduce the (D–H) factor into the electrostatic interaction, since proteins interact within an ionic medium. This formulation implies the appearance of an exponential decay factor r_D, which is the thickness of the ionic atmosphere surrounding protein molecules. The distance adopted by two interacting monomers in a protein assembly is affected by both types of interaction and therefore is a function of both r_H and r_D. In a number of cases, the electrostatic interaction between D vectors is repulsive, generating a potential barrier that monomers are able to cross thanks to an overwhelmingly attractive hydrophobic potential well. In other cases both interactions are attractive and the distance between monomers appears as a compromise of both r_H and r_D.

The simulation of analytical ultracentrifugation data in the sedimentation velocity (SV) mode is extremely useful for experimental planning and hypothesis testing. However, undertaking such simulations can be daunting, especially if one is unpracticed in SV analytic software and the underlying hydrodynamic precepts of the method. Recently, to address this need, the software SViMULATE was introduced. This software featured a simple user interface and facile, on-the-fly conversions of familiar macromolecular properties (e.g., molar mass, shape) to the quantities needed for a successful SV simulation (the sedimentation coefficient, s, and the translational diffusion coefficient, D_T). The software offered an easy route to simulate an unlimited number of species, and two experimental modes, normal and difference SV, were enabled. In the current work, features added to SViMULATE since its initial release are detailed. These include new experimental modes: two interacting systems, nonideal sedimentation, flotation, and band (or “analytical zone”) SV. Further, the modeling of polydisperse species as a series of related individual species has been enabled, and more sophisticated radial and time discretizations enhance the numerical stability of the simulation engine. These features significantly expand the scope and utility of the software, and the advances described herein are immediately available in version 1.4.0 of SViMULATE.

After the elastic regime is surpassed, cortical bone exhibits significant microcracking in its post-elastic mechanical behavior. This work develops a thermodynamically consistent, nonlinear constitutive model based on statistical mechanics, designed to predict the stress–strain relationship and the progression of inter-osteon microcracking. To assess the model’s sufficiency, precise tensile and bending tests were performed in comparison to empirical curves that illustrated theoretical predictions of constitutive relationships. Moreover, entropy increases were quantitatively assessed using model parameters refined through experimental data. A large-size sample was utilized, comprising 51 dog-bone-shaped cortical bone specimens from the 4th ribs of various subjects for uniaxial tensile tests, and 15 complete fourth ribs for bending tests. Displacement and strain fields were meticulously recorded using digital image correlation and video analysis. The model demonstrated robustness, accurately fitting the data from all experimental specimens and revealing correlations between constitutive parameters and anthropometric variables. Entropy calculations provide insights into the behavior of the bone under varying strains: microcracking is minimal at low strains with stress nearly proportional to strain, escalating significantly beyond a critical threshold, thus challenging the linear relationship between stress and strain.

Association of a ligand with the binding site of a receptor is usually at least a two-step process - formation of an initial encounter complex followed by a conformational transition of the complex. Consequently, the description of binding by dimeric receptors requires a two-dimensional reaction scheme. An interesting example of a dimeric receptor is the decapping scavenger enzyme, DcpS. It is a critical determinant of mRNA metabolism that hydrolyses the 5’-end (hbox {m}^7)GpppN cap following 3’-end mRNA decay. The DcpS family of proteins function as homodimers with one active site in each protomer. We investigate the binding of substrate and product analogues of the mRNA cap, (hbox {m}^7)Gp((hbox {CH}_2))ppG and (hbox {m}^7)GMP, respectively, by human DcpS wild-type ((hbox {DcpS}^{mathrm {WT/WT}})) and its one-site compromised mutant ((hbox {DcpS}^{mathrm {WT/BC}})) using stopped-flow fluorimetry. Based on observations for the mutant (hbox {DcpS}^{mathrm {WT/BC}}), binding by each active site and for each ligand proceeds through the formation of an encounter complex followed by conformational transitions. In the case of (hbox {DcpS}^{mathrm {WT/WT}}), we show that only two association rate constants, one for the apo-enzyme with both sites empty and the second for the enzyme with one site already occupied, can be determined with satisfactory accuracy from experimental progress curves, even for experimental data with a high signal-to-noise ratio. An interesting and biologically relevant observation is that binding of substrate analogue by one site prevents binding by the remaining empty site, whereas in the case of the (hbox {m}^7)GMP product both sites bind ligand independently of the binding state of the other site.

The self-assembly of the cobaltabis(dicarbollide) (COSAN) anionic boron clusters into micelles above a critical micelle concentration (cmc) of 10–20 mM and its behavior as “sticky nano-ions” facilitating controlled protein aggregation have been previously investigated using scattering techniques. These techniques effectively provide average structural parameters but, when applied to colloidal systems, often rely on models assuming polydispersity or anisotropic shapes. Here, we employed sedimentation velocity analytical ultracentrifugation (SV-AUC), which offers the ability to resolve discrete species. We revisited two key questions: (1) the aggregation behavior of COSAN into micelles, a topic still under debate, and (2) the nature of the protein assemblies induced by COSAN, specifically their size/shape distribution and aggregation number. SV-AUC confirms the cmc of COSAN of 16 mM and reveals that COSAN micelles exhibit low aggregation numbers (8 in water and 14 in dilute salt), consistent with recent hypotheses. It shows that COSAN promotes myoglobin aggregation into discrete oligomeric species with well-defined aggregation numbers, such as dimers, tetramers, and higher-order assemblies, depending on the COSAN-to-protein ratio. COSAN binding could be quantified at the lower COSAN/myoglobin ratios. For example, at ratio 5, myoglobin monomer (25%) binds about two COSANs, dimer (45%) about 14 COSANs, and there are ≈ 30% very large aggregates. These results provide clarity on the discrete nature of COSAN micelle aggregation and protein assembly. This study highlights the complementary role of SV-AUC in understanding supramolecular assemblies, offering useful insights into the behavior of COSAN nano-ions and their interactions with biomacromolecules.

Biomembranes regulate molecular transport essential to cellular function and numerous biomedical applications, such as drug delivery and gene therapy. This study simulates molecular transport through nano-sized multipores in Giant Unilamellar Vesicles (GUVs) using COMSOL Multiphysics. We analyzed the diffusion dynamics of fluorescent probes—including Calcein, Texas-red dextran 3000 (TRD- 3k), TRD- 10k, and Alexa Fluor-labeled soybean trypsin inhibitor (AF-SBTI)—across different pore sizes, and derived rate constants using curve fitting that closely align with experimental data. Additionally, an analytical model based on Fick’s law of diffusion provides further insight into transport efficiency. This approach offers a novel perspective by examining simultaneous transport through multiple nanopores, which better mimics realistic biological environments compared to traditional single-pore studies. We used COMSOL for efficiently simulating large-scale, multi-nanopore systems, particularly in biomedical applications where modeling of complex transport phenomena is essential. This work provides new insights into multipore-mediated transport, critical for optimizing nanopore-based drug delivery and advancing the understanding of cellular transport mechanisms.

Water is central to biological processes not only as a solvent, but also as an agent shaping macromolecular behavior. Insights into water micro assemblies (WMA), defined by transient regions of low-density water (LDW) and high-density water (HDW), have highlighted their potential impact on biological phenomena. LDW, with its structured hydrogen bonding networks and reduced density, stabilizes hydrophobic interfaces and promotes ordered molecular configurations. Conversely, HDW, with its dynamic and flexible nature, facilitates transitions, solute mobility and molecular flexibility. By correlating experimental observations with simulations, we explore the influence of WMA on three key biological processes. In protein folding, LDW may stabilize hydrophobic cores and secondary structures by forming structured exclusion zones, while HDW may introduce dynamic flexibility, promoting the resolution of folding intermediates and leading to dynamic rearrangements. In enzyme catalysis, LDW may form structured hydration shells around active sites stabilizing active sites over longer timescales, while HDW may support substrate access and catalytic flexibility within active sites. In membrane dynamics, LDW may stabilize lipid headgroups, forming structured hydration layers that enhance membrane rigidity and stability, while HDW may ensure the nanosecond-scale flexibility required for vesicle formation and fusion. Across these tree processes, the WMA’s energy contributions, timescales and spatial scales align with the forces and dynamics involved, highlighting the role of LDW and HDW in modulating cellular interactions. This perspective holds implications for the design of lab-on-chip devices, advancements in sensor technologies, development of biomimetic membranes for drug delivery, creation of novel therapeutics and deeper understanding of protein misfolding diseases.

Exocytosis is a fundamental process related to the information exchange in the nervous and endocrine system. Among the various techniques, vesicle impact electrochemical cytometry (VIEC) has emerged as an effective method to mimic the exocytosis process and measure dynamic information about content transfer using nanoscale electrodes. In this article, through analytical models and large scale simulations, we develop scaling laws for the decay time constant ((tau )) for VIEC single-exponential transients. Specifically, our results anticipate a power law dependence of (tau) on the geometric and the transport parameters. This model compares very well with large scale simulations exploring the parameter space relevant for VIEC and with experimental results from literature. Remarkably, such physics-based compact models could allow for novel multi-feature-based self consistent strategies for back extraction of geometric and transport parameters and hence could contribute towards better statistical analysis and understanding of exocytosis transients and events.