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Related Concept Videos

Coat Assembly and GTPases01:33

Coat Assembly and GTPases

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Vesicles incorporate different coat protein subunits in different cell locations, which changes the properties of the coat, such as the shape and geometry of the transport vesicles. Thus, vesicle coat proteins also play a significant role in cargo selection.
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Rab Proteins01:14

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Rab proteins constitute the largest family of monomeric GTPases, of which 70 members are present in humans. Rab proteins and their effectors regulate consecutive stages of vesicle transport such as vesicle transport, docking, and fusion to the correct recipient membrane.
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Rab GTPases act in a regulated cascade during membrane fusion, helping the lipid bilayers mix. The Rab family of proteins are active when bound to GTP, and inactive when bound to GDP. Hence, they act as guanine nucleotide-dependent molecular switches. Rab-GTP recognizes and binds to long or short-range tethering proteins to capture the target vesicle. These tethers coordinate with SNAREs on the vesicle and the target membrane to assemble the trans SNARE complex that locks the mixing bilayers.
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Nuclear protein sorting regulates nucleus composition and gene expression, crucial for determining the fate of a eukaryotic cell. Hence, the entry and exit of molecules across the nuclear envelope is a tightly controlled process. Nuclear protein sorting can be inhibited by one of the following ways: 1) masking cargo signal sequences, 2) modifying the nuclear receptor's affinity for cargo, 3) controlling the nuclear pore size, 4) retaining the cargo during its transit to the cytosol or the...
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Mechanism of Lamellipodia Formation01:31

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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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Ras and Rho are small monomeric GTPases that act downstream of receptor tyrosine kinase (RTK) and regulate various cellular processes. These GTPases switch between active and inactive states by binding to guanine nucleotides.
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Related Experiment Video

Updated: Jun 23, 2025

Automated Imaging and Analysis for the Quantification of Fluorescently Labeled Macropinosomes
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Automated Imaging and Analysis for the Quantification of Fluorescently Labeled Macropinosomes

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Leep2A and Leep2B function as a RasGAP complex to regulate macropinosome formation.

Xiaoting Chao1,2, Yihong Yang1, Weibin Gong1

  • 1Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.

The Journal of Cell Biology
|June 18, 2024
PubMed
Summary
This summary is machine-generated.

Researchers discovered Leep2, a Ras GTPase-activating protein (GAP) complex, which is crucial for regulating macropinocytosis, a cellular process for bulk fluid uptake. Fine-tuning Ras activity via Leep2 is essential for proper macropinosome formation.

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Area of Science:

  • Cell biology
  • Molecular signaling
  • Biochemistry

Background:

  • Macropinocytosis is a conserved cellular process for bulk fluid uptake, essential for nutrient acquisition and environmental sensing.
  • Ras GTPases are central regulators of macropinocytosis, but their upstream regulation and spatiotemporal control remain unclear.
  • Understanding the molecular mechanisms governing Ras signaling in macropinocytosis is critical for deciphering cellular uptake processes.

Purpose of the Study:

  • To identify novel regulators of macropinocytosis using a proteomics-based approach in the model organism Dictyostelium.
  • To elucidate the role of the identified complex in the spatiotemporal regulation of Ras GTPase activity during macropinosome formation.
  • To investigate how modulation of this complex and its target Ras GTPases affects macropinocytic activity.

Main Methods:

  • Proteomics-based screening in Dictyostelium to identify proteins involved in macropinocytosis regulation.
  • Biochemical assays to characterize the function of the identified Leep2 complex as a Ras GTPase-activating protein (GAP).
  • Genetic manipulation (deletion, overexpression) of Leep2 and target Ras GTPases to assess their impact on macropinocytosis.

Main Results:

  • Identification of Leep2 (composed of Leep2A and Leep2B) as a novel RasGAP complex crucial for macropinocytosis.
  • Localization of the Leep2 complex to forming macropinocytic cups and nascent macropinosomes.
  • Demonstration that Leep2 modulates the activity of three Ras family small GTPases, thereby regulating macropinosome formation.
  • Observed impairment of macropinocytosis upon deletion or overexpression of Leep2, or disruption/sustained activation of target Ras GTPases.

Conclusions:

  • The Leep2 complex plays a critical role in the spatiotemporal regulation of Ras signaling during macropinocytosis.
  • Fine-tuning Ras GTPase activity is essential for efficient and controlled macropinosome formation.
  • This study reveals a key regulatory mechanism governing cellular bulk fluid uptake.