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Energy to Drive Translocation

Energy to Drive Translocation

Mitochondrial protein import is powered by two distinct energy sources: ATP hydrolysis and electrochemical potential across the inner membrane. Newly synthesized precursors are bound by cytosolic chaperones of the Hsp70 family, which guide them to the import receptors on the mitochondrial surface. Utilizing the energy of ATP hydrolysis, Hsp70 chaperones transfer these precursors to the TOM receptors on the mitochondrial outer membrane.
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Molecular Chaperones and Protein Folding

Molecular Chaperones and Protein Folding

The native conformation of a protein is formed by interactions between the side chains of its constituent amino acids. When the amino acids cannot form these interactions, the protein cannot fold by itself and needs chaperones. Notably, chaperones do not relay any additional information required for the folding of polypeptides; the native conformation of a protein is determined solely by its amino acid sequence. Chaperones catalyze protein folding without being a part of the folded protein.
The...

Molecular Chaperones and Protein Folding

Molecular Chaperones and Protein Folding

The native conformation of a protein is formed by interactions between the side chains of its constituent amino acids. When the amino acids cannot form these interactions, the protein cannot fold by itself and needs chaperones. Notably, chaperones do not relay any additional information required for the folding of polypeptides; the native conformation of a protein is determined solely by its amino acid sequence. Chaperones catalyze protein folding without being a part of the folded protein.
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Mitochondrial Precursor Proteins

Mitochondrial Precursor Proteins

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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Mitochondrial Protein Sorting

Mitochondrial Protein Sorting

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...

Translocation of Proteins into the Mitochondria

Translocation of Proteins into the Mitochondria

Mitochondrial precursors are translocated to the internal subcompartments via independent mechanisms involving distinct protein machineries called translocases.
Sorting of outer membrane proteins:
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Understanding the functional interplay between mammalian mitochondrial Hsp70 chaperone machine components.

Arvind Vittal Goswami¹, Balasubramanyam Chittoor, Patrick D'Silva

¹Department of Biochemistry, Indian Institute of Science, Bangalore 560012, Karnataka, India.

The Journal of Biological Chemistry

|April 16, 2010

Summary

Human mitochondrial Hsp70 (mtHsp70) chaperone machinery components were reconstituted and analyzed. Human mtHsp70 shows unique interactions and regulation, with Hsp70 escort protein (Hep) playing a key role.

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Area of Science:

Mitochondrial biology
Molecular chaperones
Protein import

Background:

Mitochondrial biogenesis relies on cytosolic protein import.
The mitochondrial heat shock protein 70 (mtHsp70) machinery is crucial and conserved in eukaryotes.
Functional characterization of human mtHsp70 components across eukaryotic families is incomplete.

Purpose of the Study:

To reconstitute and analyze the in vitro biochemical functions of the human mtHsp70 chaperone machine.
To investigate the functional interactions among human mtHsp70, J-proteins, GrpE, and Hsp70 escort protein (Hep).
To compare the functional properties of human mtHsp70 with its yeast counterpart.

Main Methods:

Reconstitution of the mtHsp70 chaperone machine components (Hsp70/J-protein/GrpE/Hep).
In vitro biochemical analysis of component interactions and functions.
Characterization of human mtHsp70 binding specificity and ATPase activity regulation.

Main Results:

Human mtHsp70 exhibits distinct sequence-specific interactions with mitochondrial client proteins compared to yeast Ssc1.
The helical lid of human mtHsp70 is dispensable for P5 peptide binding.
Human Hsp70 escort protein (Hep) uniquely stimulates mtHsp70 ATPase activity and prevents client protein aggregation.
Hep interacts with the C-terminus of mtHsp70, distinct from client or J-protein binding, and its interaction is regulated by the helical lid.
Hep binding to the ATPase domain is mutually exclusive with J-proteins, promoting ATPase stimulation.

Conclusions:

The human mtHsp70 machinery possesses unique regulatory mechanisms and client interactions.
Hsp70 escort protein (Hep) plays a multifaceted role in mtHsp70 function, distinct from J-proteins.
Understanding these mechanisms provides insights into mitochondrial protein import and potential links to diseases like myelodysplastic syndrome.