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The Cell Membrane in the Steady State
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Membrane proteins, whether of the integral or peripheral type, perform a variety of functions in addition to those previously mentioned in (1). They act as receptors that mediate various forms of communication or signaling between the cytoplasm and the external environment and as enzymes that partake in the production of substances required for cell functioning. Glycoproteins, which are proteins having covalently bonded carbohydrate chains, are found on the external surface of the membrane and are involved in cell–cell interactions, such as in cell recognition and rejection. These processes are part of the immune response and also allow similar cells to adhere together to form tissues. Proteins on the inner surface of the membrane can be part of the cytoskeleton (Section 1.1.4). It is seen that, far from being a passive envelope that contains the cytoplasm, the cell membrane performs many functions that are vital to the cell.
Functional Study of Lysosomal Nutrient Transporters
Published in Bruno Gasnier, Michael X. Zhu, Ion and Molecule Transport in Lysosomes, 2020
Xavier Leray, Corinne Sagné, Bruno Gasnier
Resident membrane proteins are targeted to the lysosome from the trans-Golgi network either directly via the endosomes or indirectly by default routing to the plasma membrane followed by internalization into the endocytic pathway. In both cases, short sequence motives present in their cytosolic domains are recognized by adaptor proteins that drive their incorporation into protein-coated vesicles which eventually uncoat and fuse with the target membrane (Braulke and Bonifacino, 2009). Mutation of key residues in these motives impairs the recognition step, resulting in default delivery of the mutated protein to the plasma membrane.
Atomic Force Microscopy of Biomembranes
Published in Qiu-Xing Jiang, New Techniques for Studying Biomembranes, 2020
Yi Ruan, Lorena Redondo-Morata, Simon Scheuring
Membrane proteins are proteins that interact with or are inserted in biological membranes. Those embedded in cell membranes serve a critical purpose in the maintenance of many cellular functions, including signal transduction, cell integrity, intracellular and extracellular transport, cell-to-cell communication, etc. In principle, membrane proteins are mainly divided into two categories: peripheral membrane proteins, integral membrane proteins. The former may temporarily or permanently go through lipids, covalent link to lipids, or bind to other proteins in membranes, while the latter are permanently embedded in the membrane. The new features of HS-AFM enable us to analyze dynamics of membrane proteins, such as how single membrane proteins move, how they interact with other membrane proteins, their oligomeric state and conformational changes, etc., we will describe some of these studies in the following.
Protective role of PERK-eIF2α-ATF4 pathway in chronic renal failure induced injury of rat hippocampal neurons
Published in International Journal of Neuroscience, 2023
Qi Chen, Jingjing Min, Ming Zhu, Zhanqin Shi, Pingping Chen, Lingyan Ren, Xiaoyi Wang
The endoplasmic reticulum is one of the most important organelles in eukaryotic cells. It is not only the site for protein translation and synthesis as well as calcium ion storage, but also a participant in the transmission and processing of various cell signals. In addition, one of the major functions of the endoplasmic reticulum is to serve as a site for synthesizing secretory and integral membrane proteins.5,6 When cells are stimulated by hypoxia, an imbalance of calcium ions or a change in their concentration occurs in the internal environment, accompanied with the accumulation of some unfolded proteins in the endoplasmic reticulum, resulting in an imbalance between the structure and function of the endoplasmic reticulum. At this time, the corresponding signal pathway is activated to further trigger the endoplasmic reticulum stress (ERS) response.7 Unfolded protein response activation can be triggered in the following three ways: (1) inhibition of protein translation to prevent the production of more folded proteins; (2) induction of the folding of unfolded proteins by the endoplasmic reticulum chaperone; (3) activation of endoplasmic reticulum associated degradation pathways to remove unfolded proteins accumulated in the endoplasmic reticulum.8 However, under prolonged or severe stress, the unfolded protein response initiates programmed cell death.
Surface-modified polymeric nanoparticles for drug delivery to cancer cells
Published in Expert Opinion on Drug Delivery, 2021
Arsalan Ahmed, Shumaila Sarwar, Yong Hu, Muhammad Usman Munir, Muhammad Farrukh Nisar, Fakhera Ikram, Anila Asif, Saeed Ur Rahman, Aqif Anwar Chaudhry, Ihtasham Ur Rehman
Cell membrane functions as the main barrier for inward and outward movement of bio-entities [33]. Similarly, drug-loaded polymeric nanoparticles are also needed to cross the cell membrane to exhibit their efficiency. The composition, morphology, and functions of cell membrane have attracted scientists to fabricate nanoparticles, whose surfaces mimic cell membrane (Figure 3a). The cell membrane is composed of a phospholipid bilayer with embedded proteins and carbohydrates. Phospholipids consist of hydrophobic phosphate group-containing head linked to the hydrophobic tail of fatty acids. These phospholipids self-assemble into bilayers with hydrophilic regions facing toward outside and inside of the cell, while hydrophobic tails of phospholipids face each other. The incorporation of cholesterol and proteins enhances the stability of the cell membrane. Membrane proteins are inserted throughout the cell membrane asymmetrically. They are arranged in a way that their exterior surfaces can act as receptors for signaling molecules, whereas interior sides change their conformation in response to the binding signal. In some cases, membrane carbohydrates, in the form of glycolipids, work as recognition sites for proteins [34]. Research on biologically inspired nanoparticles has revealed that surface modification of nanoparticles with lipid bilayer or protein/carbohydrate embedding enhances the efficacy of drug-loaded nanoparticles [35], for instance increase in circulation time, improved biocompatibility, low toxicity and immunogenicity [36] and enhanced stability [37].
Recent advances in cell membrane-camouflaged nanoparticles for inflammation therapy
Published in Drug Delivery, 2021
Rongtao Zhang, Siqiong Wu, Qian Ding, Qingze Fan, Yan Dai, Shiwei Guo, Yun Ye, Chunhong Li, Meiling Zhou
Cell membranes and vesicles derived from them are asymmetric phospholipid bilayers that may contain thousands of unique membrane proteins that are essential for their biological functions (van Meer, 2011). Methods commonly used to fuze membranes include extrusion, ultrasonic fusion and electroporation. Recently, nitrogen cavitation has been used to disrupt cells and generate pure, membrane-bound nanovesicles (Gao et al., 2016, 2017). Subsequent differential centrifugation can purify the nanovesicles away from other intracellular contents of the parent cells (Wang et al., 2018). In order to minimize the denaturation of membrane proteins, the extraction and purification of cell membranes must be performed under as mild conditions as possible. To maintain their biological activity, the prepared cell membranes should be used immediately, or they may be aliquoted and stored at −80 °C, sometimes in the presence of protease inhibitors to prevent membrane protein degradation (Gao et al., 2015; Hu et al., 2015). The precise extraction approach depends on whether the source cell contains a nucleus.