Protein condensates as flexible platforms for membrane traffic

Dynamic Duos: Coacervate-Lipid Membrane Interactions in Regulating Membrane Transformation and Condensate Size

Biomolecular condensates interfacing with lipid membranes is crucial for several key cellular functions. However, the role of lipid membranes in regulating condensates in cells remains obscure. Here, in-depth interactions between condensates and lipid membranes are probed and unraveled by employing cell-mimetic systems like Giant unilamellar vesicles (GUVs). An unprecedented influence of the coacervate size and their electrostatic interaction with lipid membranes is revealed on the membrane properties and deformation. Importantly, these findings demonstrate that the large relative size of coacervates and minimal electrostatic interaction strength with membranes allow for budding transitions at the interface. Membranes act as nucleation site for coacervates when the charge-charge interaction is high, giving a wrinkled vesicle surface appearance. Molecular diffusion property of lipids, quantified using Fluorescence recovery after photobleaching (FRAP), is modulated at the coacervate-membrane interaction site restricting the coarsening of coacervates. Notably, these results reveal coacervate droplets are intertwined in between membrane folds and invaginations discerned using Transmission electron microscopy (TEM) and high-resolution imaging, which further controls the dimension of droplets resembling size distributions observed in cells. Finally, these findings provide mechanistic insights of lipid bilayers controlling condensate sizes that play a prominent role in comprehending nucleation and localization of cellular condensates.

Lysosome Functions in Atherosclerosis: A Potential Therapeutic Target

Lysosomes in mammalian cells are recognized as key digestive organelles, containing a variety of hydrolytic enzymes that enable the processing of both endogenous and exogenous substrates. These organelles digest various macromolecules and recycle them through the autophagy-lysosomal system. Recent research has expanded our understanding of lysosomes, identifying them not only as centers of degradation but also as crucial regulators of nutrient sensing, immunity, secretion, and other vital cellular functions. The lysosomal pathway plays a significant role in vascular regulation and is implicated in diseases such as atherosclerosis. During atherosclerotic plaque formation, macrophages initially engulf large quantities of lipoproteins, triggering pathogenic responses that include lysosomal dysfunction, foam cell formation, and subsequent atherosclerosis development. Lysosomal dysfunction, along with the inefficient degradation of apoptotic cells and the accumulation of modified low-density lipoproteins, negatively impacts atherosclerotic lesion progression. Recent studies have highlighted that lysosomal dysfunction contributes critically to atherosclerosis in a cell- and stage-specific manner. In this review, we discuss the mechanisms of lysosomal biogenesis and its regulatory role in atherosclerotic lesions. Based on these lysosomal functions, we propose that targeting lysosomes could offer a novel therapeutic approach for atherosclerosis, shedding light on the connection between lysosomal dysfunction and disease progression while offering new insights into potential anti-atherosclerotic strategies.

The conserved protein adaptors CALM/AP180 and FCHo1/2 cooperatively recruit Eps15 to promote the initiation of clathrin-mediated endocytosis in yeast

Clathrin-mediated endocytosis (CME) is a critical trafficking process that begins when an elaborate endocytic protein network is established at the plasma membrane. Interaction of early endocytic proteins with anionic phospholipids and/or cargo has been suggested to trigger CME initiation. However, the exact mechanism by which CME sites are initiated has not been fully elucidated. In the budding yeast Saccharomyces cerevisiae, higher levels of anionic phospholipids and cargo molecules exist in the newly formed daughter cell compared to the levels in the mother cell during polarized growth. Taking advantage of this asymmetry, we quantitatively compared CME proteins in S. cerevisiae mother versus daughter cells, observing differences in the dynamics and composition of key endocytic proteins. Our results show that CME site initiation occurs preferentially on regions of the plasma membrane with a relatively higher density of endocytic cargo and/or acidic phospholipids. Furthermore, our combined live cell-imaging and yeast genetics analysis provided evidence for a molecular mechanism in which CME sites are initiated when Yap1801 and Yap1802 (yeast CALM/AP180) and Syp1 (yeast FCHo1/2) coordinate with anionic phospholipids and cargo molecules to trigger Ede1 (yeast Eps15)-centric CME initiation complex assembly at the plasma membrane.

Protein condensates in the the secretory pathway: Unraveling biophysical interactions and function

The emergence of phase separation phenomena among macromolecules has identified biomolecular condensates as fundamental cellular organizers. These condensates concentrate specific components and accelerate biochemical reactions without relying on membrane boundaries. Although extensive studies have revealed a large variety of nuclear and cytosolic membraneless organelles, we are witnessing a surge in the exploration of protein condensates associated with the membranes of the secretory pathway, such as the endoplasmic reticulum and the Golgi apparatus. This review focuses on protein condensates in the secretory pathway and discusses their impact on the organization and functions of this cellular process. Moreover, we explore the modes of condensate-membrane association and the biophysical and cellular consequences of protein condensate interactions with secretory pathway membranes.

Ion channel trafficking implications in heart failure

Heart failure (HF) is recognized as an epidemic in the contemporary world, impacting around 1%-2% of the adult population and affecting around 6 million Americans. HF remains a major cause of mortality, morbidity, and poor quality of life. Several therapies are used to treat HF and improve the survival of patients; however, despite these substantial improvements in treating HF, the incidence of HF is increasing rapidly, posing a significant burden to human health. The total cost of care for HF is USD 69.8 billion in 2023, warranting a better understanding of the mechanisms involved in HF. Among the most serious manifestations associated with HF is arrhythmia due to the electrophysiological changes within the cardiomyocyte. Among these electrophysiological changes, disruptions in sodium and potassium currents' function and trafficking, as well as calcium handling, all of which impact arrhythmia in HF. The mechanisms responsible for the trafficking, anchoring, organization, and recycling of ion channels at the plasma membrane seem to be significant contributors to ion channels dysfunction in HF. Variants, microtubule alterations, or disturbances of anchoring proteins lead to ion channel trafficking defects and the alteration of the cardiomyocyte's electrophysiology. Understanding the mechanisms of ion channels trafficking could provide new therapeutic approaches for the treatment of HF. This review provides an overview of the recent advances in ion channel trafficking in HF.