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Mitochondrial Membranes

Mitochondrial Membranes

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,...

Mitochondrial Membranes

Mitochondrial Membranes

Structure of Porins

Structure of Porins

Mitochondria, chloroplasts, and gram-negative bacteria have transmembrane, beta-barrel proteins called porins to mediate the free diffusion of ions and metabolites across the membrane. Mitochondrial porin precursors contain conserved amino acid sequences called beta signals at their C-terminal. Beta signals have a motif of PoXGXXHyXHy (Po-Polar, X-Any amino acid, G-Glycine, Hy-LargeHydrophobic), which are crucial for precursor recognition to initiate precursor assembly. Beta-barrel...

Porin Insertion in the Outer Mitochondrial Membrane

Porin Insertion in the Outer Mitochondrial Membrane

Porins are beta-barrel proteins translocated to the mitochondrial outer membrane through the TOM complex into the intermembrane space. Porin precursors bind TIM chaperones within the intermembrane space and are guided to the Sorting and Assembly Machinery complex or SAM complex on the outer mitochondrial membrane.
Three models describe the assembly of porins by the SAM complex and their insertion into the outer membrane. Model 1 suggests that porins are assembled outside the SAM channel as the...

The Inner Mitochondrial Membrane

The Inner Mitochondrial Membrane

The inner mitochondrial membrane is the primary site of ATP synthesis. The inner membrane domain that forms a smooth layer adjacent to the outer membrane is called the inner boundary membrane. This domain contains membrane transporters that drive metabolites in and out of the mitochondria. In contrast, the inner membrane network that invaginates into the matrix space is called the cristae membrane. This domain accounts for principle mitochondrial function as it accommodates the protein...

Protein Transport into the Inner Mitochondrial Membrane

Protein Transport into the Inner Mitochondrial Membrane

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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Using Scaffold Liposomes to Reconstitute Lipid-proximal Protein-protein Interactions In Vitro

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VDAC-2: Mitochondrial outer membrane regulator masquerading as a channel?

Svetlana Rajkumar Maurya¹, Radhakrishnan Mahalakshmi¹

¹Molecular Biophysics Laboratory, Department of Biological Sciences, Indian Institute of Science Education and Research, Bhopal, India.

The FEBS Journal

|December 29, 2015

Summary

Voltage-dependent anion channels (VDACs) are crucial for cell metabolism and death regulation. This study decodes the unique anti-apoptotic functions of VDAC-2, linking its structure to specific cellular roles beyond simple transport.

Keywords:

apoptosis cysteines mitochondrial outer membrane voltage-dependent anion channel β-barrel proteins

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Area of Science:

Mitochondrial biology
Cellular transport
Apoptosis regulation

Background:

Voltage-dependent anion channels (VDACs) are essential for mitochondrial transport and cellular metabolism.
VDACs play a critical role in regulating apoptosis, the process of programmed cell death.
While VDAC-1's role in apoptosis and homeostasis is established, VDAC-2's function has been debated, though it's known for anti-apoptotic properties in humans.

Purpose of the Study:

To associate functional studies of VDAC-2 with structural data to understand its unique behavior.
To elucidate the specific regulatory functions and anti-apoptotic features of VDAC-2.
To explore VDAC-2's contribution to gametogenesis and other cellular pathways.

Main Methods:

Integration of existing functional data on VDAC-2.
Analysis of structural reports concerning VDAC-2.
Comparative analysis of VDAC-2 structural features against other VDAC isoforms, particularly VDAC-1.

Main Results:

VDAC-2 possesses unique structural features, including a well-structured N-terminus, compact barrel, distinct loop regions, specific transmembrane segments, and abundant thiols.
These structural attributes enable VDAC-2 to perform specialized regulatory functions, confer anti-apoptotic properties, and contribute to gametogenesis.
VDAC-2's structure suggests a primary role in regulating reactive oxygen species, steroidogenesis, and mitochondria-associated endoplasmic reticulum membrane pathways, with ion transport being a secondary function.

Conclusions:

VDAC-2's unique structure dictates its distinct functional roles compared to VDAC-1.
The specific structural characteristics of VDAC-2 underpin its anti-apoptotic activity and involvement in gametogenesis.
Understanding VDAC family structural nuances can guide the development of targeted inhibitors for VDAC-related pathway dysregulation.