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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.
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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.
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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.
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A peptide bond covalently attaches amino acids through a dehydration reaction. One amino acid's carboxyl group and another amino acid's amino group combine, releasing a water molecule. The resulting bond is the peptide bond. The products that such linkages form are peptides. As more amino acids join this growing chain, the resulting chain is a polypeptide. Each polypeptide has a free amino group at one end. This end has the N-terminal, or the amino-terminal, and the other end has a free...
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Protein digestion begins in the stomach, where the highly acidic environment can easily disrupt protein structure by exposing the peptide bonds of polypeptide chains. After polypeptide chains are broken into individual amino acids by a series of digestive enzymes, the amino acids are transported to the liver via the bloodstream to produce energy.
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Linear Peptides in Intracellular Applications.

Cristiane R Zuconelli1, Roland Brock2, Merel J W Adjobo-Hermans1

  • 1Department of Biochemistry, Radboud Institute for Molecular Life Sciences, Radboud University Nijmegen Medical Center, Nijmegen, Netherlands.

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Linear, unmodified peptides are surprisingly stable within cells and can modulate intracellular signaling. This challenges the long-held belief that structural modifications are always necessary for therapeutic peptide applications.

Keywords:
Synthetic peptidesbioactive endogenous peptidesintracellular signalingintracellular peptidespeptide deliverypeptide stability

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Cell Biology

Background:

  • Therapeutic peptide development for intracellular use has focused on stability, often assuming unmodified peptides are rapidly degraded.
  • This assumption stems largely from research on peptide degradation during antigen processing, not general intracellular stability.
  • Endogenous peptides, however, demonstrate stability and bioactivity within cells, influencing signaling pathways.

Purpose of the Study:

  • To review the exploration and application of linear, unmodified peptides for intracellular applications.
  • To challenge the prevailing notion that structural modifications are essential for peptide stability and efficacy.
  • To highlight the potential of unmodified peptides in modulating intracellular signaling.

Main Methods:

  • Review of existing literature on intracellular peptide turnover, stability, and bioactivity.
  • Analysis of studies employing synthetic linear, unmodified peptides for intracellular signaling modulation.
  • Examination of techniques used to measure peptide stability and delivery methods.

Main Results:

  • Unmodified linear peptides can exhibit significant stability within cells, contrary to previous assumptions.
  • Synthetic unmodified peptides can reach biologically relevant concentrations and demonstrate desired activity.
  • Endogenous peptides naturally function within cells, modulating signaling pathways without chemical modifications.

Conclusions:

  • Linear, unmodified peptides represent a viable and potentially underestimated class of therapeutic agents for intracellular applications.
  • Future research should focus on understanding the rules governing the stability and predictive design of such peptides.
  • The paradigm for therapeutic peptide design may need re-evaluation to include unmodified linear structures.