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Two very polarized views exist for understanding the cellular plasma membrane (PM). For some, it is the simple fluid described by the original Singer–Nicolson fluid mosaic model. For others, due to the presence of thousands of molecular species that extensively interact with each other, the PM forms various clusters and domains that are constantly changing and therefore, no simple rules exist that can explain the structure and molecular dynamics of the PM. In this article, we propose that viewing the PM from its two predominant components, cholesterol and actin filaments, provides an excellent and transparent perspective of PM organization, dynamics, and mechanisms for its functions. We focus on the actin-induced membrane compartmentalization and lipid raft domains coexisting in the PM and how they interact with each other to perform PM functions. This view provides an important update of the fluid mosaic model.

Dysregulated mitochondrial fusion and fission has been implicated in the pathogenesis of numerous diseases. We have identified a novel function of the p53 family protein TAp73 in regulating mitochondrial dynamics. TAp73 regulates the expression of Optic atrophy 1, a protein responsible for controlling mitochondrial fusion, cristae biogenesis and electron transport chain function. Disruption of this axis results in a fragmented mitochondrial network and an impaired capacity for energy productionviaoxidative phosphorylation. Owing to the role of OPA1 in modulating cytochromecrelease, TAp73-/-cells also display an increased sensitivity to apoptotic cell death, e.g.,viaBH3-mimetics. We also show that the TAp73/OPA1 axis has functional relevance in the upper airway, where TAp73 expression is essential for multiciliated cell differentiation and function. Consistently, ciliated epithelial cells ofTrp73-/-(global p73 KO) mice display decreased expression of OPA1 and perturbations of the mitochondrial network, which may drive multiciliated cell loss. In support of this,Trp73andOPA1gene expression is decreased in COPD patients, a disease characterised by alterations in mitochondrial dynamics. We therefore highlight a potential mechanism involving the loss of p73 in COPD pathogenesis. This work also adds to the growing body of evidence for growth-promoting roles of TAp73 isoforms.

Exposure to brake abrasion dust (BAD) reduces the phagocytic capacity of macrophages, possibly contributing to increased risk of airway infections in polluted regions. The mechanisms that underlie this toxicity remain to be characterised and, considering that pre-exposure of respiratory bacteria to alternative traffic-related particulates enhances their dissemination into the lungs of mice, may include changes in the virulence of pathogens themselves. Dual proteomic screening (TMT-labelled UPLC-MS) was performed for RAW 264.7 monocyte-derived macrophages and S.aureus (USA300) following 24h exposures to BAD (0-16 ug/ml). In S.aureus, expression of agr-regulated, anti-leukocytic virulence factors (lipases, staphopains, hemolysins) increased in a dose-dependent manner as well as proteins required for epithelial invasion (serine proteases) and antibiotic resistance. RAW 264.7 exhibited a predominantly adaptive response following exposures, enhancing expression of proteins required for metal homeostasis, NFkB-mediated inflammation and endosomal maturation. However, disrupted expression of proteins required for electron transport chain activity and Fe-S cluster synthesis accompanied significant dose-dependent reductions in ATP production (60-82%, p< 0.001) while transition electron microscopy (TEM) detected disrupted mitochondrial membrane morphology. TEM also identified reductions in pseudopodia length in exposed macrophages (54% shorter than control, p< 0.05), highlighting a mechanism by which BAD exposure may decrease the incidence of host-pathogen interactions. These data highlight dual mechanisms by which BAD emissions could impair bacterial phagocytosis and enhance susceptibility to airway infections. Through avoidance and suppression of host anti-microbial mechanisms by the bacteria and, as actin polymerisation depends on ATP availability, loss of mitochondrial function and downstream pseudopodia projection in macrophages.

Single-molecule intramolecular dynamics were successfully measured for three variants of the SARS-CoV-2 spike protein, alpha: B.1.1.7, delta: B.1.617, omicron: B.1.1.529, with a time resolution of 100 microseconds using X-rays and we compared the results in respects to the magnitude and directions of motions for three variants. The largest 3-D intramolecular movement (=40 mrad2/ms) were observed for the omicron variant with and without ACE2 receptor binding. The smallest movement (=20 mrad2/ms) was observed in the alpha variant. A more detailed analysis of the intramolecular motions revealed that the intramolecular motion distribution state of the three variants showed a complete difference in binding and nonbinding to the ACE2 receptor. Interestingly, in the spike variant without ACE2 receptors, the alpha and delta variants showed a clockwise bias in the direction of rotational motions, while only the omicron variant showed an anticlockwise bias in rotational motion. However, when the ACE2 receptor was bound, all variants exhibited an anticlockwise-biased rotational motion. This information is very important for early assessment of the cell invasion process and the infectivity of the variants.