Biology subjects

Weiner, B. G.

Publications and source records attributed to Weiner, B. G..

3 recordsLinked to original sources

bioRxiv2020

Sequence dependence of biomolecular phase separation

Cells are home to a wide variety of biomolecular condensates - phase-separated droplets that lack a membrane. In addition to nonspecific interactions, phase separation depends on specific binding motifs between constituent molecules. Nevertheless, few rules have been established on how these specific, heterotypic interactions drive phase separation. Using lattice-polymer simulations and mean-field theory, we show that the sequence of binding motifs strongly affects a polymers ability to phase separate, influencing both phase boundaries and condensate properties (e.g. viscosity and polymer diffusion). We find that sequences with large blocks of a single motif typically form more inter-polymer bonds which promote phase separation. Notably, the sequence of binding motifs influences phase separation primarily by determining the conformational entropy of self-bonding by single polymers. This contrasts with systems where the molecular architecture primarily affects the energy of the dense phase, providing a new entropy-based mechanism for the biological control of phase separation.

biophysics↗

bioRxiv2020

Decoding the physical principles of two-component biomolecular phase separation

Cells possess a multiplicity of non-membrane bound compartments, which form via liquid-liquid phase separation. These condensates assemble and dissolve as needed to enable central cellular functions. One important class of condensates is those composed of two associating polymer species that form one-to-one specific bonds. What are the physical principles that underlie phase separation in such systems? To address this question, we employed coarse-grained molecular dynamics simulations to examine how the phase boundaries depend on polymer valence, stoichiometry, and binding strength. We discovered a striking phenomenon - for sufficiently strong binding, phase separation is suppressed at rational polymer stoichiometries, which we termed the magic-ratio effect. We further developed an analytical dimer-gel theory that confirmed the magic-ratio effect and disentangled the individual roles of polymer properties in shaping the phase diagram. Our work provides new insights into the factors controlling the phase diagrams of biomolecular condensates, with implications for natural and synthetic systems.

biophysics↗

bioRxiv2019

Spatial Ecology of Territorial Populations

Many ecosystems, from vegetation to biofilms, are composed of territorial populations that compete for both nutrients and physical space. What are the implications of such spatial organization for biodiversity? To address this question, we developed and analyzed a model of territorial resource competition. In the model, all species obey trade-offs inspired by biophysical constraints on metabolism; the species occupy non-overlapping territories while nutrients diffuse in space. We find that the nutrient diffusion time is an important control parameter for both biodiversity and the timescale of population dynamics. Interestingly, fast nutrient diffusion allows the populations of some species to fluctuate to zero, leading to extinctions. Moreover, territorial competition spontaneously gives rise to both multistability and the Allee effect (in which a minimum population is required for survival), so that small perturbations can have major ecological effects. While the assumption of trade-offs allows for the coexistence of more species than the number of nutrients - thus violating the principle of competitive exclusion - overall biodiversity is curbed by the domination of \"oligotroph\" species. Importantly, in contrast to well-mixed models, spatial structure renders diversity robust to inequalities in metabolic trade-offs. Our results suggest that territorial ecosystems can display high biodiversity and rich dynamics simply due to competition for resources in a spatial community.

ecology↗