More Like this

1. Semipermeable Mixed Phospholipid-Fatty Acid Membranes Exhibit K+/Na+ Selectivity in the Absence of Proteins

   https://doi.org/10.3390/life10040039  

   Zhou, Xianfeng; Dalai, Punam; Sahai, Nita (April 2020, Life)

   Two important ions, K+ and Na+, are unequally distributed across the contemporary phospholipid-based cell membrane because modern cells evolved a series of sophisticated protein channels and pumps to maintain ion gradients. The earliest life-like entities or protocells did not possess either ion-tight membranes or ion pumps, which would result in the equilibration of the intra-protocellular K+/Na+ ratio with that in the external environment. Here, we show that the most primitive protocell membranes composed of fatty acids, that were initially leaky, would eventually become less ion permeable as their membranes evolved towards having increasing phospholipid contents. Furthermore, these mixed fatty acid-phospholipid membranes selectively retain K+ but allow the passage of Na+ out of the cell. The K+/Na+ selectivity of these mixed fatty acid-phospholipid semipermeable membranes suggests that protocells at intermediate stages of evolution could have acquired electrochemical K+/Na+ ion gradients in the absence of any macromolecular transport machinery or pumps, thus potentially facilitating rudimentary protometabolism. 

   more » « less
2. Hybrid Protocells Based on Coacervate‐Templated Fatty Acid Vesicles Combine Improved Membrane Stability with Functional Interior Protocytoplasm

   https://doi.org/10.1002/smll.202406671  

   Lee, Jessica; Pir_Cakmak, Fatma; Booth, Richard; Keating, Christine_D (October 2024, Small)

   Abstract Prebiotically‐plausible compartmentalization mechanisms include membrane vesicles formed by amphiphile self‐assembly and coacervate droplets formed by liquid–liquid phase separation. Both types of structures form spontaneously and can be related to cellular compartmentalization motifs in today's living cells. As prebiotic compartments, they have complementary capabilities, with coacervates offering excellent solute accumulation and membranes providing superior boundaries. Herein, protocell models constructed by spontaneous encapsulation of coacervate droplets by mixed fatty acid/phospholipid and by purely fatty acid membranes are described. Coacervate‐supported membranes form over a range of coacervate and lipid compositions, with membrane properties impacted by charge–charge interactions between coacervates and membranes. Vesicles formed by coacervate‐templated membrane assembly exhibit profoundly different permeability than traditional fatty acid or blended fatty acid/phospholipid membranes without a coacervate interior, particularly in the presence of magnesium ions (Mg²⁺). While fatty acid and blended membrane vesicles are disrupted by the addition of Mg²⁺, the corresponding coacervate‐supported membranes remain intact and impermeable to externally‐added solutes. With the more robust membrane, fluorescein diacetate (FDA) hydrolysis, which is commonly used for cell viability assays, can be performed inside the protocell model due to the simple diffusion of FDA and then following with the coacervate‐mediated abiotic hydrolysis to fluorescein. 

   more » « less
3. Physical insights into biological memory using phospholipid membranes

   https://doi.org/10.1140/epje/s10189-023-00391-7  

   Bolmatov, Dima; Collier, C Patrick; Katsaras, John; Lavrentovich, Maxim O (January 2024, The European Physical Journal E)

   Electrical signals may propagate along neuronal membranes in the brain, thus enabling communication between nerve cells. In doing so, lipid bilayers, fundamental scaffolds of all cell membranes, deform and restructure in response to such electrical activity. These changes impact the electromechanical properties of the membrane, which then physically store biological memory. This memory can exist either over a short or long period of time. Traditionally, biological memory is defined by the strengthening or weakening of transmissions between individual neurons. Here, we show that electrical stimulation may also alter the properties of the lipid membrane, thus pointing toward a novel mechanism for memory storage. Furthermore, based on the analysis of existing electrophysiological data, we study molecular mechanisms underlying the long-term potentiation in phospholipid membranes. Finally, we examine possible relationships between the memory capacitive properties of lipid membranes, neuronal learning, and memory. 

   more » « less
4. Creating cross-linked lamellar block copolymer supporting layers for biomimetic membranes

   https://doi.org/10.1039/C8FD00044A  

   Lang, Chao; Shen, Yue-xiao; LaNasa, Jacob A.; Ye, Dan; Song, Woochul; Zimudzi, Tawanda J.; Hickner, Michael A.; Gomez, Enrique D.; Gomez, Esther W.; Kumar, Manish; et al (January 2018, Faraday Discussions)

   The long-standing goal in membrane development is creating materials with superior transport properties, including both high flux and high selectivity. These properties are common in biological membranes, and thus mimicking nature is a promising strategy towards improved membrane design. In previous studies, we have shown that artificial water channels can have excellent water transport abilities that are comparable to biological water channel proteins, aquaporins. In this study, we propose a strategy for incorporation of artificial channels that mimic biological channels into stable polymeric membranes. Specifically, we synthesized an amphiphilic triblock copolymer, poly(isoprene)– block –poly(ethylene oxide)– block –poly(isoprene), which is a high molecular weight synthetic analog of naturally occurring lipids in terms of its self-assembled structure. This polymer was used to build stacked membranes composed of self-assembled lamellae. The resulting membranes resemble layers of natural lipid bilayers in living systems, but with superior mechanical properties suitable for real-world applications. The procedures used to synthesize the triblock copolymer resulted in membranes with increased stability due to the crosslinkability of the hydrophobic domains. Furthermore, the introduction of bridging hydrophilic domains leads to the preservation of the stacked membrane structure when the membrane is in contact with water, something that is challenging for diblock lamellae that tend to swell, and delaminate in aqueous solutions. This new method of membrane fabrication offers a practical model for making channel-based biomimetic membranes, which may lead to technological applications in reverse osmosis, nanofiltration, and ultrafiltration membranes. 

   more » « less
5. Rapid and Sequential Dual Oxime Ligation Enables De Novo Formation of Functional Synthetic Membranes from Water‐Soluble Precursors

   https://doi.org/10.1002/anie.202200549  

   Flores, Judith; Brea, Roberto J.; Lamas, Alejandro; Fracassi, Alessandro; Salvador‐Castell, Marta; Xu, Cong; Baiz, Carlos R.; Sinha, Sunil K.; Devaraj, Neal K. (June 2022, Angewandte Chemie International Edition)

   Abstract Cell membranes define the boundaries of life and primarily consist of phospholipids. Living organisms assemble phospholipids by enzymatically coupling two hydrophobic tails to a soluble polar head group. Previous studies have taken advantage of micellar assembly to couple single‐chain precursors, forming non‐canonical phospholipids. However, biomimetic nonenzymatic coupling of two alkyl tails to a polar head‐group remains challenging, likely due to the sluggish reaction kinetics of the initial coupling step. Here we demonstrate rapid de novo formation of biomimetic liposomes in water using dual oxime bond formation between two alkyl chains and a phosphocholine head group. Membranes can be generated from non‐amphiphilic, water‐soluble precursors at physiological conditions using micromolar concentrations of precursors. We demonstrate that functional membrane proteins can be reconstituted into synthetic oxime liposomes from bacterial extracts in the absence of detergent‐like molecules. 

   more » « less