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Related Concept Videos

Mechanisms of Membrane-bending01:15

Mechanisms of Membrane-bending

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The living membranes are flexible due to their fluid mosaic nature; however, their bending into different shapes is an active process regulated by specific lipids and proteins. The membrane bending can be transient as seen in vesicles or stable for a long time as in microvilli. Cells regulate the size, location, and duration of the membrane curvature.
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Actin is a family of globular proteins that are highly abundant in eukaryotic cells. It makes up approximately 1-5% of total cell protein concentration. Actin monomers polymerize to form a complex network of polarized filaments, the actin cytoskeleton, that plays a crucial role in many cellular processes, including cell motility, division, endocytosis, and metastasis of cancer cells.
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Filopodia are thin, actin-rich cellular protrusions that play an important role in many fundamental cellular functions. They vary in their occurrence, length, and positioning in different cell types, suggesting their diverse roles.
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The straight or branched structure formation of actin filaments is controlled by nucleating proteins such as the formins and Arp2/3 complex. Formin-mediated assembly results in straight filaments, whereas Arp2/3 protein complex-mediated assembly results in branched actin filaments.
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Cells migrating in response to external stimuli form lamellipodia, which are thin membrane protrusions supported by a mesh of linked, branched, or unbranched actin filaments. These actin filaments interact with myosin motor proteins, creating the dynamic actomyosin complex within the cytoskeleton. Contractility, or the ability to generate contractile stress, is inherent to the actomyosin complex. It helps cells detect the stiffness of the surrounding ECM and exert contractile force for...
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Actin polymerization occurs through the head-to-tail association of binding sites on monomeric actin or G-actin to form filamentous or F-actin. The polymerization can be divided into three phases ̶  nucleation, elongation, and steady-state phase.
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Membrane composition and curvature in SNX9-mediated actin polymerization.

Pankti Vaishnav1,2, Hanae Shimo Kondo1,2, Jonathan R Gadsby1,2

  • 1Gurdon Institute, University of Cambridge, Cambridge CB2 1QN, United Kingdom.

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Sorting nexin 9 (SNX9) is a scaffold protein involved in viral uptake and cancer. This study reveals SNX9

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Area of Science:

  • Biochemistry
  • Cell Biology
  • Molecular Medicine

Background:

  • Sorting nexin 9 (SNX9) is a scaffold protein implicated in viral uptake, inflammation, and cancer progression.
  • SNX9 participates in endocytosis and the formation of mitochondrial-derived vesicles.
  • Its Bin-Amphiphysin-Rvs (BAR)-Phox homology (PX) domains bind phosphoinositides, and its Src homology 3 (SH3) domain interacts with proteins regulating actin polymerization.

Purpose of the Study:

  • To investigate the membrane-binding specificity and actin-remodeling activities of SNX9.
  • To elucidate the structural mechanisms underlying SNX9's functions at the membrane.

Main Methods:

  • Biolayer interferometry to assess binding affinities.
  • Cell-free reconstitution assays to study protein interactions.
  • Superresolution microscopy (3D-STORM) and cryo-electron tomography to visualize SNX9 structures and actin networks.

Main Results:

  • SNX9 exhibits preferential binding to liposomes containing PI(4,5)P2 and PI(3)P over PI(3,4)P2.
  • Actin assembly is dependent on the combined interactions of SNX9's PX-BAR and SH3 domains.
  • SNX9 forms both flat and curved assemblies at actin incorporation sites and builds branched and bundled actin networks.

Conclusions:

  • SNX9 possesses multifunctional capabilities in actin remodeling.
  • Its specific membrane interactions and ability to organize actin networks highlight its critical roles in cellular processes.
  • Understanding SNX9's mechanisms may offer insights into cancer and viral pathogenesis.