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Related Concept Videos

Translocation of Proteins into the Mitochondria01:19

Translocation of Proteins into the Mitochondria

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Mitochondrial precursors are translocated to the internal subcompartments via independent mechanisms involving distinct protein machineries called translocases.
Sorting of outer membrane proteins:
Mitochondrial outer membrane proteins are of two types: the transmembrane, beta-barrel porins, and the membrane-anchored, alpha-helical proteins. Beta-barrel porin precursors are translocated by the TOM complex and inserted into the outer mitochondrial membrane by the SAM complex. In contrast,...
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Protein Transport into the Inner Mitochondrial Membrane01:34

Protein Transport into the Inner Mitochondrial Membrane

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Nuclear encoded mitochondrial precursors are imported to the inner membrane in a multistep process involving two separate translocons, TIM22 and TIM23. TIM23 is a cation-selective pore that remains closed by the N terminal segment of the protein. Negative charges on the TIM23 act as a receptor for the incoming precursor, pulling the positively charged matrix-targeting sequence for peptide insertion and translocation.
Transport of mitochondrial precursors across the TIM23 channel is driven by...
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Mitochondrial Protein Sorting01:39

Mitochondrial Protein Sorting

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Mitochondria are double-membrane organelles of the eukaryotes involved in cellular metabolism, signaling, ATP synthesis, and programmed cell death.  Each of these processes requires specific proteins and enzymes that must be correctly sorted to the right mitochondrial subcompartment for the proper functioning of the organelle.
Most of these mitochondrial proteins are encoded by the nucleus and imported to the mitochondria as unfolded or loosely folded precursors. Mitochondrial precursors...
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Mitochondrial Precursor Proteins01:39

Mitochondrial Precursor Proteins

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Mitochondrial precursors are partially unfolded or loosely folded polypeptide chains. Newly synthesized precursors are inhibited from spontaneously folding into their native conformation by the cytosolic chaperones, heat shock proteins 70 (Hsp70), and mitochondrial import stimulation factors (MSFs). Precursors bound to MSFs are guided to the TOM70-TOM37 receptors, while precursors bound to Hsp70  chaperones are targetted to TOM20-TOM22 receptor complexes.
Most of the mitochondrial...
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Calmodulin-dependent Signaling01:16

Calmodulin-dependent Signaling

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Calmodulin (CaM) is a calcium-binding protein in eukaryotes that controls various calcium-regulated cellular processes. It has four calcium-binding sites that bind calcium to form the calcium-calmodulin ( Ca2+-CaM) complex. GPCR stimulation increases the calcium levels in the cells that bind to CaM and induces a conformational change.
The Ca2+-CaM complex does not have enzymatic activity by itself. Instead, the complex binds downstream target proteins, including membrane proteins or enzymes,...
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Mitochondrial Membranes01:45

Mitochondrial Membranes

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A single mitochondrion is a bean-shaped organelle enclosed by a double-membrane system. The outer membrane of mitochondria is smooth and contains many porins - the integral membrane transporters. Porins enable free diffusion of ions and small uncharged molecules through the outer mitochondrial membrane but limit the transport of molecules larger than 5000 Daltons. Further, the outer mitochondrial membrane forms a unique structure called membrane contact sites with other subcellular organelles,...
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Related Experiment Video

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Analyses of Mitochondrial Calcium Influx in Isolated Mitochondria and Cultured Cells
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Analyses of Mitochondrial Calcium Influx in Isolated Mitochondria and Cultured Cells

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Mitochondrial Ca2+ uptake pathways.

Pia A Elustondo1, Matthew Nichols2, George S Robertson2

  • 1Department of Physiology and Biophysics, Faculty of Medicine, Dalhousie University, B3H 4R2, Halifax, NS, Canada.

Journal of Bioenergetics and Biomembranes
|September 26, 2016
PubMed
Summary

Mitochondrial calcium uptake is primarily mediated by the Mitochondrial Calcium Uniporter (MCU). However, even without MCU, mitochondria retain some calcium, suggesting alternative calcium entry pathways exist.

Keywords:
CalciumExchangerInorganic polyphosphateIon channelMitochondriaPermeability transition porePolyhydroxybutyrateUniporter

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Mitochondrial Ca2+ Retention Capacity Assay and Ca2+-triggered Mitochondrial Swelling Assay
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Simultaneous Measurement of Mitochondrial Calcium and Mitochondrial Membrane Potential in Live Cells by Fluorescent Microscopy
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Mitochondrial Ca2+ Retention Capacity Assay and Ca2+-triggered Mitochondrial Swelling Assay
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Simultaneous Measurement of Mitochondrial Calcium and Mitochondrial Membrane Potential in Live Cells by Fluorescent Microscopy
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Area of Science:

  • Cell Biology
  • Biochemistry
  • Physiology

Background:

  • Calcium (Ca2+) is vital for cellular functions, acting as a structural element, signaling molecule, and regulator of cellular processes.
  • Mitochondria utilize Ca2+ for energy production and stress response, with uptake occurring via the uniporter mechanism.
  • The Mitochondrial Calcium Uniporter (MCU) protein is identified as the primary component for mitochondrial Ca2+ uptake.

Purpose of the Study:

  • To review evidence for alternative Ca2+ influx mechanisms into mitochondria.
  • To explore the role of these alternative pathways in mitochondrial Ca2+ signaling.
  • To understand the implications of MCU-independent Ca2+ uptake.

Main Methods:

  • Review of experimental evidence on mitochondrial Ca2+ transport.
  • Analysis of MCU knockout (MCU KO) studies.
  • Discussion of cellular signaling pathways involving calcium.

Main Results:

  • MCU KO studies show reduced but not abolished mitochondrial Ca2+ uptake.
  • Essential cellular functions like muscle contraction and neurotransmission are not abolished in MCU KO.
  • Low but detectable Ca2+ levels persist in MCU KO mitochondria.

Conclusions:

  • The existence of unrecognized pathways for Ca2+ entry into mitochondria is suggested.
  • These alternative pathways may play an integral role in mitochondrial Ca2+ signaling.
  • Further research is needed to identify and characterize these alternative Ca2+ influx mechanisms.