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Cholesterol plays a crucial role in biomembranes by regulating various properties such as fluidity, rigidity, permeability, and organization of lipid bilayers. The latest version of the Martini model, Martini 3, offers significant improvements in interaction balance, molecular packing, and the inclusion of new bead types and sizes. However, the release of the new model resulted in the need to re-parameterize many core molecules, including cholesterol. Here, we describe the development and validation of a Martini 3 cholesterol model, addressing issues related to its bonded setup, shape, volume and hydrophobicity. The proposed model mitigates some limitations of its Martini 2 predecessor while maintaining or improving overall behavior.

In the erythrocyte membrane, the interactions between glycophorin A (GPA) and Band 3 are associated strongly with the biological function of the membrane and several blood disorders. In this work, using coarse-grained molecular-dynamics simulations, we systematically investigate the effects of cholesterol and phosphatidylinositol-4,5-bisphosphate (PIP2) on the interactions of GPA with Band 3 in the model erythrocyte membranes. We examine the dynamics of the interactions of GPA with Band 3 in different lipid bilayers on the microsecond time scale and calculate the binding free energy between GPA and Band 3. The results indicate that cholesterols thermodynamically favor the binding of GPA to Band 3 by increasing the thickness of the lipid bilayer and by producing an effective attraction between the proteins due to the depletion effect. Cholesterols also slow the kinetics of the binding of GPA to Band 3 by reducing the lateral mobility of the lipids and proteins and may influence the binding sites between the proteins. The anionic PIP2 lipids prefer binding to the surface of the proteins through electrostatic attraction between the PIP2 headgroup and the positively charged residues on the protein surface. Ions in the solvent facilitate PIP2 aggregation, which promotes the binding of GPA to Band 3.

Data for the publication "Martini 3 force field parameters for protein lipidation post-translational modifications" in the Journal of Chemical Theory and Computation Protein lipidations are vital co-translational or post-translational modifications that tether lipid tails to specific protein aminoacids to allow them to anchor to biological membranes, switch their subcellular localizations, and modulate association with other proteins. Such lipidations are thus crucial for multiple biological processes such as signal transduction, protein trafficking and membrane localization, and are implicated in various diseases as well. Examples of such lipid-anchored proteins include the Ras family of proteins that undergo farnesylation, actin and gelsolin, which are myristoylated, phospholipase D, which is palmitoylated, glycosylphosphatidylinositol-anchored proteins and others. Here, we develop parameters for the latest version of the Martini 3 coarse-grained force field for cysteine-targeting farnesylation, geranylgeranylation and palmitoylation as well as the glycine-targeting myristoylation due to the importance of these lipidations in disease and in particular for studying cancer and anti-cancer drug discovery. The parameters are developed using the CHARMM36m all-atom force field parameters as reference. The behavior of the coarse-grained models is consistent with that of the all-atom force field for all lipidations and reproduces key dynamical and structural features such as solvent-accessible surface area, bilayer penetration depth, and cluster representative conformations. The parameters, along with mapping schemes for the popular martinize2 tool, are immediately available for download.

Peripheral myelin protein 2 (P2) plays an important role in the stacking of the myelin membrane and lipid transport. Here we investigate the interactions between P2 and a model myelin membrane using molecular dynamics simulations, focusing on the effect of the L27D mutation and conformational changes in the α2-helix in the lid domain of P2. The L27D mutation weakens the binding of the lid domain of P2 on the membrane. The α2-helix is either folded or unfolded on the membrane. Compared with the α2-helix structure in water, the membrane stabilizes the structure of the α2-helix, whereas the unfolding of the α2-helix reduces the binding affinity of P2 on the membrane. These findings reveal the energetics of the mutant and the structural changes of P2 on the interactions between the protein and the lipid bilayer and help us to understand the microscopic mechanism of the formation of the myelin sheath structure and some neurological disorders.

As the past century has been characterized by waves of viral pandemics, there is an ever-growing role for molecular simulation-based research. In this study, we utilize all-atom molecular dynamics to simulate an enterovirus-D68 capsid and examine the dependency of viral capsid dynamics and properties on AMBER and CHARMM force fields. Out of the six force fields studied, we note that CHARMM36m and CHARMM36 generate secondary structures that are most consistent with protein structural data and sample the largest conformational space. The ion distribution and radius of gyration of the capsid are similar across all force fields investigated.

Past efforts to synthesize and quantify the magnitude and change in carbon dioxide (CO2) fluxes in terrestrial ecosystems across the rapidly warming Arctic–boreal zone (ABZ) have provided valuable information but were limited in their geographical and temporal coverage. Furthermore, these efforts have been based on data aggregated over varying time periods, often with only minimal site ancillary data, thus limiting their potential to be used in large-scale carbon budget assessments. To bridge these gaps, we developed a standardized monthly database of Arctic–boreal CO2 fluxes (ABCflux) that aggregates in situ measurements of terrestrial net ecosystem CO2 exchange and its derived partitioned component fluxes: gross primary productivity and ecosystem respiration. The data span from 1989 to 2020 with over 70 supporting variables that describe key site conditions (e.g., vegetation and disturbance type), micrometeorological and environmental measurements (e.g., air and soil temperatures), and flux measurement techniques. Here, we describe these variables, the spatial and temporal distribution of observations, the main strengths and limitations of the database, and the potential research opportunities it enables. In total, ABCflux includes 244 sites and 6309 monthly observations; 136 sites and 2217 monthly observations represent tundra, and 108 sites and 4092 observations represent the boreal biome. The database includes fluxes estimated with chamber (19 % of the monthly observations), snow diffusion (3 %) and eddy covariance (78 %) techniques. The largest number of observations were collected during the climatological summer (June–August; 32 %), and fewer observations were available for autumn (September–October; 25 %), winter (December–February; 18 %), and spring (March–May; 25 %). ABCflux can be used in a wide array of empirical, remote sensing and modeling studies to improve understanding of the regional and temporal variability in CO2 fluxes and to better estimate the terrestrial ABZ CO2 budget. ABCflux is openly and freely available online (Virkkala et al., 2021b, https://doi.org/10.3334/ORNLDAAC/1934).

The coronavirus disease 19 (COVID-19) pandemic is causing a global health crisis and has already caused a devastating societal and economic burden. The pathogen, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has a high sequence and architecture identity with SARS-CoV, but far more people have been infected by SARS-CoV-2. Here, combining the structural data from cryo-electron microscopy and structure prediction, we constructed bottom-up Martini coarse-grained models of intact SARS-CoV and SARS-CoV-2 envelopes. Microsecond molecular dynamics simulations were performed, allowing us to explore their dynamics and supramolecular organization. Both SARS-CoV and SARS-CoV-2 envelopes present a spherical morphology, with structural proteins forming multiple string-like islands in the membrane and clusters between the heads of spike proteins. Critical differences between the SARS-CoV and SARS-CoV-2 envelopes are the interaction pattern between the spike proteins and the flexibility of the spike proteins. Our models provide structural and dynamic insights into the SARS virus envelopes and could be used for further investigation, such as drug design and membrane fusion and fission processes.