Shape fluctuations and elastic properties of two-component bilayer membranes

The elastic properties of two-component bilayer membranes are studied using a coarse grain model for amphiphilic molecules. The two species of amphiphiles considered here differ only in their length. Molecular Dynamics simulations are performed in order to analyze the shape fluctuations of the two-component bilayer membranes and to determine their bending rigidity. Both the bending rigidity and its inverse are found to be nonmonotonic functions of the mole fraction $x_{\rm B}$ of the shorter B-amphiphiles and, thus, do not satisfy a simple lever rule. The intrinsic area of the bilayer also exhibits a nonmonotonic dependence on $x_{\rm B}$ and a maximum close to $x_{\rm B} \simeq 1/2$.Comment: To appear on Europhysics Letter

Role of Bilayer Tilt Difference in Equlibrium Membrane Shapes

Lipid bilayer membranes below their main transition have two tilt order parameters, corresponding to the two monolayers. These two tilts may be strongly coupled to membrane shape but only weakly coupled to each other.We discuss some implications of this observation for rippled and saddle phases, spontaneous breaking bilayer tubules, and bicontinuous phases. Tilt difference introduces a lengthscale into the elastic theory of tilted fluid membranes. It can drive an instability of the flat phase; it also provides a simple spontaneous breaking of inversion symmetry seen in some recent experiments

ValuED: A Blockchain-based Trading Platform to EncourageStudent Engagement in Higher Education

The provision of higher education has been changing ever more quickly in the UK and worldwide, as a result of technological, economic, and geopolitical factors. The Covid-19 pandemic has accelerated such changes. The “student experience”—the interaction of students with their institution and with each other—has been changing accordingly, with less face-to-face contact. In this work, we have explored a way to improve student engagement in higher education. We describe “ValuED”, a blockchain-based trading platform using a cryptocurrency. It allows students both to buy and sell goods and services within their university community and to be rewarded for academic engagement. ValuED involves a reputation system to further incentivise participants. We describe the implementation and piloting of this platform and draw conclusions for its future use. The platform’s source code is publicly available

Computational Approaches to Explore Bacterial Toxin Entry into the Host Cell

Many bacteria secrete toxic protein complexes that modify and disrupt essential processes in the infected cell that can lead to cell death. To conduct their action, these toxins often need to cross the cell membrane and reach a specific substrate inside the cell. The investigation of these protein complexes is essential not only for understanding their biological functions but also for the rational design of targeted drug delivery vehicles that must navigate across the cell membrane to deliver their therapeutic payload. Despite the immense advances in experimental techniques, the investigations of the toxin entry mechanism have remained challenging. Computer simulations are robust complementary tools that allow for the exploration of biological processes in exceptional detail. In this review, we first highlight the strength of computational methods, with a special focus on all-atom molecular dynamics, coarse-grained, and mesoscopic models, for exploring different stages of the toxin protein entry mechanism. We then summarize recent developments that are significantly advancing our understanding, notably of the glycolipid–lectin (GL-Lect) endocytosis of bacterial Shiga and cholera toxins. The methods discussed here are also applicable to the design of membrane-penetrating nanoparticles and the study of the phenomenon of protein phase separation at the surface of the membrane. Finally, we discuss other likely routes for future development

How arbitrary is language?

It is a long established convention that the relationship between sounds and meanings of words is essentially arbitrary-typically the sound of a word gives no hint of its meaning. However, there are numerous reported instances of systematic sound meaning mappings in language, and this systematicity has been claimed to be important for early language development. In a large-scale corpus analysis of English, we show that sound-meaning mappings are more systematic than would be expected by chance. Furthermore, this systematicity is more pronounced for words involved in the early stages of language acquisition and reduces in later vocabulary development. We propose that the vocabulary is structured to enable systematicity in early language learning to promote language acquisition, while also incorporating arbitrariness for later language in order to facilitate communicative expressivity and efficiency

A Theoretical Perspective on Parasite-Host Coevolution with Alternative Modes of Infection

We investigate how natural selection shapes the coevolution of parasitism. We discuss the antagonism fuelled by parasites’ necessity to transmit to novel hosts, and host’s desire to minimise virulence. In support, we build a mathematical model which considers the epidemiology and life-history trade-offs faced by an obligate microparasite and its host. Our model allows parasites to be transmitted to new hosts via direct contact (horizontally) or from parent to offspring during birth (vertically). We test the hypothesis that vertical transmission causes virulence to diminish in the long run, and contrary to widely accepted views, find that vertical transmission need not result in benign coevolutionary outcomes in general. However, vertical transmission does promotes benign parasitism whenever: it is cheap for the host to retaliate; horizontal transmission saturates quickly; or the intrinsic growth rate of the host population is low