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Related Concept Videos

Rab Cascades01:25

Rab Cascades

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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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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.
Rab proteins switch between a cytosolic, GDP-bound inactive state and a membrane-anchored, GTP-bound active state. By themselves, Rabs show slow rates of GDP/GTP exchange and GTP hydrolysis. Thus, Rab proteins are considered...
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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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The early endosome containing internalized molecules matures through transformations in its location, morphology, intraluminal pH, and membrane protein composition. Together, these changes result in a more acidic late endosome that contains multiple intraluminal vesicles; therefore, the late endosome is also called a multivesicular body (MVB).
Changes in location
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Intralumenal Vesicles and Multivesicular Bodies01:38

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Intraluminal vesicles (ILVs) are small vesicles 50-80 nm in diameter formed during the maturation of early endosomes. A specialized endosome containing numerous ILVs is called a multivesicular body (MVB). ILVs contain internalized molecules such as antigens, nucleic acids, proteins, and metabolites. Some of these molecules are released from the MVBs inside exosomes and are transported to other cells. Other MVBs contain molecules that are retained in the ILVs and are later degraded within the...
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Vesicle budding is orchestrated by distinct cytosolic proteins such as adaptor proteins, coat proteins, and GTPases. To initiate vesicle budding, membrane-bending proteins containing crescent-shaped BAR domains bind to the lipid heads in the bilayer and distort the membrane to form a protein-coated vesicle bud. Adaptors proteins such as AP2 for clathrin-coated vesicles can nucleate on the deformed membrane. Finally, coat proteins such as clathrin or COPI and COPII assemble into a coat forming...
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Endosomal maturation is controlled by the trimeric Bulli-Mon1-Ccz1 Rab7 GEF complex and the Rab5 GTPase-activating

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Researchers found GAPsec, a novel GTPase-activating protein (GAP), is essential for endosomal maturation in fruit flies. Its inactivation impairs endosome-lysosome fusion, highlighting coordinated Rab protein regulation for cellular waste clearance.

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Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • The endolysosomal system degrades cellular waste via lysosomes.
  • Endosome maturation and fusion with lysosomes are critical steps.
  • This process is regulated by tethering complexes (CORVET, HOPS) and Rab GTPases (Rab5, Rab7).

Purpose of the Study:

  • To identify novel regulators of endosomal maturation.
  • To investigate the role of GTPase-activating proteins (GAPs) in endosomal trafficking.
  • To understand the function of Rab5 regulation in fruit fly nephrocytes.

Main Methods:

  • Genetic screening in Drosophila melanogaster (fruit fly) nephrocytes.
  • Identification and characterization of novel GTPase-activating proteins (GAPs).
  • Analysis of endosomal morphology and trafficking using microscopy.

Main Results:

  • GAPsec was identified as a novel Rab5 GTPase-activating protein (GAP).
  • GAPsec is required for proper endosomal maturation in fruit fly nephrocytes.
  • Inactivation of GAPsec leads to enlarged, dysfunctional endosomes that fail to fuse with lysosomes.

Conclusions:

  • Coordinated regulation of Rab GTPases by GAPs is crucial for efficient endosomal trafficking.
  • GAPsec plays a vital role in regulating Rab5 activity during endosome maturation.
  • Dysfunctional endosomal maturation due to impaired Rab regulation hinders cellular waste degradation.