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Related Concept Videos

Overview of Secretory Vesicles01:33

Overview of Secretory Vesicles

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Secretory vesicles, also known as dense core vesicles (DCVs), are membrane-bound vesicles that transport secretory proteins, such as hormones or neurotransmitters. Regulated secretory vesicles transport proteins from the trans-Golgi network to the exterior of the cell. Proteins present in regulated secretory vesicles are required to be rapidly exocytosed in large amounts upon a specific stimulus.
Various proteins regulate the aggregation of molecules inside the secretory vesicles. Chromogranins...
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Protein Translocation Machinery on the ER Membrane01:28

Protein Translocation Machinery on the ER Membrane

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The translocon complex situated on the ER membrane is the main gateway for the protein secretory pathway. It facilitates the transport of nascent peptides into the ER lumen and their insertion into the ER membrane.
Sec61 protein conducting channel
In eukaryotes, the translocon complex comprises a core heterotrimeric translocator channel called the Sec61 complex. This channel includes three transmembrane proteins, Sec61α, Sec61β, and Sec61γ, and is the largest subunit of the...
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Role of ER in the Secretory Pathway01:17

Role of ER in the Secretory Pathway

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Eukaryotic cells have a special pathway that enables communication between various intracellular membrane-bound compartments and also with the extracellular environment. This pathway is termed as the secretory pathway.
Components of the secretory pathway
About a third of proteins synthesized in the cell are sorted via the secretory route. They shuffle between different compartments in membrane-bound vesicles until they reach their final destination. The main intracellular compartments involved...
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Vesicular Tubular Clusters01:45

Vesicular Tubular Clusters

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After budding out from the ER membrane, some COPII vesicles lose their coat and fuse with one another to form larger vesicles and interconnected tubules called vesicular tubular clusters or VTCs. These clusters constitute a compartment at the ER-Golgi interface known as ERGIC (Endoplasmic Reticulum Golgi Intermediate Compartment). The ERGIC is a mobile membrane-bound cargo transport system that sorts proteins secreted from ER and delivers them to the Golgi.
With the help of motor proteins such...
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Post-translational Translocation of Proteins to the RER01:27

Post-translational Translocation of Proteins to the RER

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A sizable fraction of proteins destined for ER are first synthesized in the cell cytosol and then transported across the ER membrane–a process called post-translational translocation. Similar to cotranslationally translocated proteins, these proteins also use the Sec translocon complex to enter the ER lumen.
Targeting proteins to the ER
Hsp40 and Hsp70 chaperone molecules bind the translated proteins in the cytosol to prevent their folding. The chaperone binding helps to keep the signal...
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Transport Across the Golgi01:26

Transport Across the Golgi

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While it is unclear how molecules move between adjacent Golgi cisternae, it is apparent that the molecules move from cis- cisterna, the entry face, to the trans- cisterna, the exit face. Experiments initially suggested vesicles that bud from one cisterna and fuse with the next cisterna to transport proteins between the cisternae. This vesicular transport model describes the Golgi apparatus as a relatively static structure with a unique enzyme composition in each cisterna. Molecules are...
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Related Experiment Video

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Investigating Mast Cell Secretory Granules; from Biosynthesis to Exocytosis
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Protein mobility within secretory granules.

Annita Ngatchou Weiss1, Mary A Bittner1, Ronald W Holz1

  • 1Department of Pharmacology, University of Michigan, Ann Arbor, Michigan.

Biophysical Journal
|July 3, 2014
PubMed
Summary

We studied how neuropeptide Y (NPY) and tissue plasminogen activator (tPA) move inside secretory granules. We found tPA moves slower than NPY, contributing to its delayed release, but doesn't fully explain it.

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Area of Science:

  • Cell Biology
  • Biophysics
  • Neuroscience

Background:

  • Neuropeptide Y (NPY) and tissue plasminogen activator (tPA) are released from chromaffin cells at different rates.
  • The molecular basis for these differing release kinetics is not fully understood.

Purpose of the Study:

  • To investigate the intra-granular mobility of NPY and tPA.
  • To correlate protein mobility with their observed release kinetics from secretory granules.

Main Methods:

  • Developed a total internal reflection (TIR) fluorescence microscopy technique to measure protein diffusion within individual secretory granules.
  • Utilized photobleaching and fluorescence recovery after photobleaching (FRAP) to assess mobility of fluorescently labeled NPY and tPA.
  • Performed numerical simulations to model protein diffusion and granule dynamics.

Main Results:

  • Tissue plasminogen activator (tPA)-cerulean exhibited significantly lower mobility within granules compared to neuropeptide Y (NPY)-cerulean.
  • Simulations indicated tPA-cerulean has a diffusion coefficient of 2 × 10⁻¹⁰ cm²/s, suggesting restricted movement.
  • While tPA's low mobility contributes to slow release, it does not solely account for the extended release duration.

Conclusions:

  • Intra-granular mobility is a key factor influencing the differential release rates of NPY and tPA.
  • tPA's restricted diffusion within secretory granules significantly slows its exit post-fusion.
  • Additional mechanisms, potentially involving tPA's role in fusion pore stabilization, are likely involved in its slow release kinetics.