Characterization of Mixed Monolayers of Phosphatidylcholine and a Dicationic Gemini Surfactant SS-1 with a Langmuir Balance: Effects Of DNA

AbstractMonolayers of a cationic gemini surfactant, 2,3-dimethoxy-1,4-bis(N-hexadecyl-N;N-dimethyl-ammonium)butane dibromide (abbreviated as SS-1) and its mixtures with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) were studied using a Langmuir balance. More specifically, we measured the force-area (π-A) curves and determined the elastic area compressibility modulus (Cs−1) as a function of lateral packing pressure and the mole fraction of the cationic lipid (XSS-1), with and without DNA in the subphase. Both SS-1 and POPC exhibited smooth compression isotherms, indicating their monolayers to be in the liquid expanded state. Even low contents (XSS-1<0.05) of SS-1 in a POPC monolayer condensed the film dramatically, up to 20% at 30mN/m. This effect is suggested to reflect reorientation of the P−-N+ dipole of the POPC headgroup. Accordingly, the magnitude of the condensing effect diminishes with XSS-1 and is not observed for mixed films of dioleoylglycerol and SS-1. Reorientation of the P−-N+ dipole is further supported by the pronounced increase in monolayer dipole potential ψ due to SS-1. The presence of DNA in the subphase affected the mixed POPC/SS-1 monolayers differently depending on the constituent lipid stoichiometry as well as on the DNA/SS-1 charge ratio. At a DNA concentration of 0.63μM (in base pairs) condensation of neat POPC monolayers was evident, and this effect remained up to XSS-1<0.5, corresponding to DNA/SS-1 charge ratio of 1.25. An expansion due to DNA, evident as an increase in ΔA/molecule, was observed at XSS-1>0.5. At a higher concentration of DNA (1.88μM base pairs) in the subphase corresponding to DNA/SS-1 charge ratio of 3.75 at XSS-1=0.5, condensation was observed at all values of XSS-1

The SARS-CoV-2 spike protein binds and modulates estrogen receptors

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) protein binds angiotensin-converting enzyme 2 as its primary infection mechanism. Interactions between S and endogenous proteins occur after infection but are not well understood. We profiled binding of S against >9000 human proteins and found an interaction between S and human estrogen receptor alpha (ER alpha). Using bioinformatics, supercomputing, and experimental assays, we identified a highly conserved and functional nuclear receptor coregulator (NRC) LXD-like motif on the S2 sub-unit. In cultured cells, S DNA transfection increased ER alpha cytoplasmic accumulation, and S treatment induced ER-dependent biological effects. Non-invasive imaging in SARS-CoV-2-infected hamsters localized lung pathology with increased ER alpha lung levels. Postmortem lung experiments from infected hamsters and humans confirmed an increase in cytoplasmic ER alpha and its colocalization with S in alveolar macrophages. These findings describe the discovery of a S-ER alpha interaction, imply a role for S as an NRC, and advance knowledge of SARS-CoV-2 biology and coronavirus disease 2019 pathology

On the proton-bound noble gas dimers (Ng-H-Ng)+ and (Ng-H-Ng')+ (Ng, Ng'= He-Xe): relationships between structure, stability, and bonding character

The structure, stability, and bonding character of fifteen (Ng-H-Ng)+ and (Ng-H-Ng')+ (Ng, Ng' = He-Xe) compounds were explored by theoretical calculations performed at the coupled cluster level of theory. The nature of the stabilizing interactions was, in particular, assayed using a method recently proposed by the authors to classify the chemical bonds involving the noble-gas atoms. The bond distances and dissociation energies of the investigated ions fall in rather large intervals, and follow regular periodic trends, clearly referable to the difference between the proton affinity (PA) of the various Ng and Ng'. These variations are nicely correlated with the bonding situation of the (Ng-H-Ng)+ and (Ng-H-Ng')+. The Ng-H and Ng'-H contacts range, in fact, between strong covalent bonds to weak, non-covalent interactions, and their regular variability clearly illustrates the peculiar capability of the noble gases to undergo interactions covering the entire spectrum of the chemical bond.3n