Articles Online Now

SIGNIFICANCE Previous work has demonstrated crowdants altered single microtubule (MT) filament elongation rates in vitro based on size- small decreased while large increased and was seen to be correlated to increased viscosity in vivo. Here we examine MT polymerization dynamics with crowdants of different sizes by in vitro reconstitution and relate crowdant size, concentration and viscosity to MT elongation and nucleation. While polymerization rate in presence of nucleating ‘seeds’ changes depending on crowdant molecular weight (size), de novo polymerization without ‘seeds’ increases regardless of crowdant size. Using a combination of quantitative microscopy and simulations, we find this crowdant size-independence emerges from the collective effect of rate limited MT nucleation and diffusion-limited elongation influenced by crowdant size.

SIGNIFICANCE This study demonstrates that synaptic morphology profoundly shapes neurotransmitter diffusion and NMDA receptor activation, directly impacting synaptic efficacy. Our model shows that factors like synaptic cleft curvature, membrane spacing, and surface area-to-volume ratio significantly influence receptor dynamics. Given the dynamic nature of dendritic spines, which change shape and size during synaptic plasticity, our findings illustrate how purely morphological changes in cleft structure can modulate interneuronal communication and signal strength.

SIGNIFICANCE: Amyloid fibrils are a form of protein aggregate associated with many neurological disorders, including Alzheimer’s disease. This has motivated extensive in vitro work to identify the aggregation mechanism as well as the effects of disease-related mutations. However, it can be challenging to extrapolate the results of these experiments to obtain their physiological relevance. Here we show that perturbations like mutations and changes to the solution conditions can have qualitatively different effects on the aggregation rate at different concentrations. Therefore, the concentration regime needs to be established in order to correctly interpret these experiments.

The outer membrane is the defining structure of Gram-negative bacteria. We previously demonstrated that it is a major load-bearing component of the cell envelope and is therefore critical to the mechanical robustness of the bacterial cell. Here, to determine the key molecules and moieties within the outer membrane that underlie its contribution to cell envelope mechanics, we measured cell-envelope stiffness across several sets of mutants with altered outer-membrane sugar content, protein content, and electric charge.

Membrane fusion is central to fundamental cellular processes such as exocytosis, when an intracellular machinery fuses membrane-enclosed vesicles to the plasma membrane for contents release. The core machinery components are the SNARE proteins. SNARE complexation pulls the membranes together, but the fusion mechanism remains unclear. A common view is that the complexation energy drives fusion, but how this energy is harvested for fusion is unexplained. Moreover, SNAREs likely fully assemble before fusion.

SIGNIFICANCE Lipid-bilayer membranes compartmentalize biological systems. Similar to translocation through pores, membrane budding controls the exchange of material and information between the compartments. In previous work, an osmotic-pressure difference has been used to drive vesicle-pore translocation; we study translocation driven by the vesicle adhering to a host membrane. Using computer simulations, we predict free, partial-translocated, and complete-translocated states. Our work may help to understand the wrapping of vesicles at plasma membranes supported by a cortical cytoskeleton and the invasion of apicomplexan parasites into their host cells.

The Hsp100 family of protein disaggregases play important roles in maintaining protein homeostasis in cells. E. coli ClpB is an Hsp100 protein that solubilizes protein aggregates. ClpB is proposed to couple the energy from ATP binding and hydrolysis to processively unfold and translocate protein substrates through its axial channel in the hexameric ring structure. However, many of the details of this reaction remain obscure. We have recently developed a transient state kinetics approach to study ClpB catalyzed protein unfolding and translocation.

Photosynthetic organisms rely on a network of light-harvesting protein-pigment complexes to efficiently absorb sunlight and transfer excitation energy to reaction centre proteins where charge separation occurs. In photosynthetic purple bacteria, these complexes are embedded within the cell membrane, with lipid composition affecting complex clustering, thereby impacting inter-complex energy transfer. However, the impact of the lipid bilayer on intra-complex excitation dynamics is less understood.

The mechanically-activated ion channel PIEZO1 is critical to numerous physiological processes, and is activated by diverse mechanical cues. The channel is gated by membrane tension and has been found to be mobile in the plasma membrane. We employed single particle tracking (SPT) of endogenous, tdTomato-tagged PIEZO1 using Total Internal Reflection Fluorescence Microscopy in live cells. Application of SPT unveiled a surprising heterogeneity of diffusing PIEZO1 subpopulations, which we labeled “mobile” and “immobile”.

α-Tocopherol (αtoc, vitamin E) is an essential nutrient sufficiently acquired through a balanced diet. This fat-soluble vitamin is most known for its antioxidative properties, however, its fundamental mechanism of action in cellular membranes remains unknown. To this end, we use time-resolved small angle neutron scattering (TR-SANS) and a contrast matching scheme to determine intervesicular exchange (kex) and intrabilayer flip-flop (kf) rates of αtoc in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) vesicles.

During the active transport of cellular cargo, forces generated by cargo-associated molecular motors propel the cargo along cytoskeletal tracks. However, the forces impact not only the cargo, but also the underlying cytoskeletal filaments. To better understand the interplay between cargo transport and the organization of cytoskeletal filaments, we employ coarse-grained computer simulations to study actin filaments interacting with cargo-anchored myosin motors in a confined domain. We show that cargo transport can lead to the segregation of filaments into domains of preferred filament polarity separated by clusters of aggregated cargoes.