Theoretical analysis of an energy barrier model for the electrical properties of a biological membrane yields new results. Discontinuities at the membrane-solution interfaces are crucial and receive careful attention, as does the polarization charge density due to electroneutral but polarized ion distributions. The topics explored include the equilibrium and time-dependent Nernst potential, the resting potential, the capacitance-resistance equation for membrane voltage, and large electrical effects on osmosis (bulk volume flow). The generalization of Nernst–Hartley salt diffusion to the diffusion of mixed salts as a necessary tool is accomplished. The electric field inside the membrane is especially strong at the membrane-solution interfaces. The analysis of the resting potential differs from the Goldman–Hodgkin–Katz formulation but predicts realistic numerical values for animal cells and also captures the effect of switching sodium and potassium ion permeabilities. An analysis of the physical basis of bulk water flow in the presence of impermeant and permeant ions, that is, Donnan osmosis, reveals large ion charge effects that have not previously been considered. The equation derived here for Donnan osmotic flow helps to explain why the action of the sodium pump is essential for the prevention of excessive osmotic stress on cellular membranes.

While the structure of proteins can now be predicted from sequence with high certainty, the prediction of protein functional dynamics remains to be achieved. Progress towards this goal will require a much larger experimental database of the relationships among sequence, dynamics, and function than currently available. Dynamic transitions that are key to protein function and turnover remain difficult to access and characterize because they have significantly higher free energy than the folded states of proteins and hence are not populated. To access these higher free energy states, proteins must be perturbed. High temperatures often lead to aggregation, while chemical denaturants, because they interact with the entire protein backbone, tend to smooth protein conformational landscapes. In contrast, high hydrostatic pressure represents a continuous and reversible variable that can perturb protein structure locally around internal cavities, leading to partial structural disruption, populating these higher energy states sufficiently for their characterization.

Single-particle electron cryomicroscopy (cryo-EM) has enabled rapid advances in our understanding of membrane protein structure and function. The primary goal during the development of cryo-EM was to perform experiments equivalent to X-ray crystallography, but without needing to crystallize the protein of interest first. However, exciting recent progress in single-particle cryo-EM has come from relaxing assumptions and constraints related to the homogeneity of samples. These assumptions and constraints, which were necessary for crystallization, include that all molecules imaged have the same composition and are in the same conformation, that the specimen consists of only one species, and that the specimen is derived from a solution of isolated protein particles. Here, I discuss the study of membrane protein complexes within lipid bilayers by single-particle cryo-EM. I point out the value and recently achieved capability of studying membrane proteins in lipid vesicles, and in particular endogenous membrane proteins in vesicles prepared from their native lipid bilayer.

Octahedral transition metal complexes are increasingly recognised as useful tools for the development of complex cations that recognise and interact with specific DNA sequences and higher-order DNA topologies. The versatility and diversity of these complexes is particularly due to their rich photophysical and electrochemical properties at the octahedral metal centre, which can be modulated by changing the surrounding ligands. While X-ray crystallography provides uniquely direct structural information on metal-DNA binding, it is one of several essential approaches; solution-state methods such as NMR and complementary biophysical studies are critical for defining predominant binding modes in solution and in biologically relevant environments. Here, we present an overview of the different binding modes of some of these octahedral transition metal complexes with DNA, emphasising the structural and biophysical studies employed to understand metal complex–DNA interactions.

Intrinsically disordered proteins (IDPs) and disordered regions of folded proteins (IDRs) perform a plethora of cellular functions involving interactions with a variety of proteins, DNA, and RNA. Their flexibility enables them to interact with different cellular components. They can adopt molten globule as well as extended statistical coil structures depending on their amino acid residue sequence. They are generally more enriched in polar and charged residues, which generally facilitate solvation. This review article asks to what extent water as a solvent affects local (on a residue level) and global properties (size, Flory exponents) of IDPs. It introduces various aspects of protein hydration in the folded state as a benchmark and reference. The results of experimental and computational studies on short model peptides reveal how local structural propensities of residues are determined by water–backbone and water–side chain interactions. Ramachandran plots of individual amino acid residues are side-chain and neighbor-dependent. For unfolded oligo-peptides and IDPs (IDRs) the article discusses the intricated relationship between IDP hydration and global parameters (i.e., radius of gyration), which involves multiple parameters such as net charge, charge distribution, hydrophobicity, and the ionic strength of the aqueous solution. A review of experimental work that explored the strength of water–protein interactions and their influence on water dynamics reveals significant differences between water binding to folded and disordered proteins. Finally, The role of water in liquid–liquid mixing of short peptides and IDPs is delineated, which can lead to gelation and the formation of membrane-less droplets.