bims-cytox1 2021-07-18 papers

Issue of 2021–07–18
three papers selected by
Gavin McStay, Staffordshire University

Mitochondrion. 2021 Jul 09. pii: S1567-7249(21)00086-6. [Epub ahead of print]

Defective Complex III Mitochondrial Respiratory Chain Due to A Novel Variant in CYC1 Gene Masquerades Acute Demyelinating Syndrome or Leber Hereditary Optic Neuropathy.

Erfan Heidari, Maryam Rasoulinezhad, Neda Pak, Mahmoud Reza Ashrafi, Morteza Heidari, Brenda Banwell, Masoud Garshasbi, Ali Reza Tavasoli.

Complex III (CIII) is the third out of five mitochondrial respiratory chain complexes residing at the mitochondrial inner membrane. The assembly of 10 subunits encoded by nuclear DNA and one by mitochondrial DNA result in the functional CIII which transfers electrons from ubiquinol to cytochrome c. Deficiencies of CIII are among the least investigated mitochondrial disorders and thus clinical spectrum of patients with mutations in CIII is not well defined. We report on a 10-year-old girl born to consanguineous Iranian parents presenting with recurrent visual loss episodes and optic nerve contrast enhancement in brain imaging reminiscent of an acquired demyelination syndrome (i.e. optic neuritis or multiple sclerosis), who was ultimately confirmed to have a novel homozygous missense variant of unknown significance, c.949C>T; p.(Arg317Trp) in the CYC1 gene, a nuclear DNA subunit of complex III of the mitochondrial chain. Sanger sequencing confirmed the segregation of this variant with disease in the family. The effect of this variant on the protein structure was shown in-silico. Our findings, not only expand the clinical spectrum due to defects in CYC1 gene but also highlight that mitochondrial respiratory chain disorders could be considered as a potential differential diagnosis in children who present with unusual patterns of acquired demyelination syndromes (ADS). In addition, our results support the hypothesis that mitochondrial disorders might have an overlapping presentation with ADS.

Keywords: CYC1; acquired demyelinating syndrome; complex III deficiency; mitochondrial leukoencephalopathy

DOI: https://doi.org/10.1016/j.mito.2021.07.001

J Cell Sci. 2021 Jul 01. pii: jcs252197. [Epub ahead of print]134(13):

Super-resolution microscopy reveals the arrangement of inner membrane protein complexes in mammalian mitochondria.

Catherine S Palmer, Jieqiong Lou, Betty Kouskousis, Elvis Pandzic, Alexander J Anderson, Yilin Kang, Elizabeth Hinde, Diana Stojanovski.

The mitochondrial inner membrane is a protein-rich environment containing large multimeric complexes, including complexes of the mitochondrial electron transport chain, mitochondrial translocases and quality control machineries. Although the inner membrane is highly proteinaceous, with 40-60% of all mitochondrial proteins localised to this compartment, little is known about the spatial distribution and organisation of complexes in this environment. We set out to survey the arrangement of inner membrane complexes using stochastic optical reconstruction microscopy (STORM). We reveal that subunits of the TIM23 complex, TIM23 and TIM44 (also known as TIMM23 and TIMM44, respectively), and the complex IV subunit COXIV, form organised clusters and show properties distinct from the outer membrane protein TOM20 (also known as TOMM20). Density based cluster analysis indicated a bimodal distribution of TIM44 that is distinct from TIM23, suggesting distinct TIM23 subcomplexes. COXIV is arranged in larger clusters that are disrupted upon disruption of complex IV assembly. Thus, STORM super-resolution microscopy is a powerful tool for examining the nanoscale distribution of mitochondrial inner membrane complexes, providing a 'visual' approach for obtaining pivotal information on how mitochondrial complexes exist in a cellular context.

Keywords: COXIV; Mitochondria; Mitochondrial complexes; Nanoscopy; Protein import; STORM; TIM23

DOI: https://doi.org/10.1242/jcs.252197

Bio Protoc. 2021 Jun 20. 11(12): e4057

Protein Import Assay into Mitochondria Isolated from Human Cells.

Lena M Murschall, Esra Peker, Thomas MacVicar, Thomas Langer, Jan Riemer.

Mitochondria are essential organelles containing approximately 1,500 proteins. Only approximately 1% of these proteins are synthesized inside mitochondria, whereas the remaining 99% are synthesized as precursors on cytosolic ribosomes and imported into the organelle. Various tools and techniques to analyze the import process have been developed. Among them, in vitro reconstituted import systems are of importance to study these processes in detail. These experiments monitor the import reaction of mitochondrial precursors that were previously radiolabeled in a cell-free environment. However, the methods described have been mostly performed in mitochondria isolated from S. cerevisiae. Here, we describe the adaptation of this powerful assay to import proteins into crude mitochondria isolated from human tissue culture cells. Graphic abstract: Overview of the assay to monitor protein import into mitochondria isolated from human cells.

Keywords: Cell-free protein synthesis; Human tissue culture cells; In organello import ; Isolated mitochondria; Radiolabeled proteins

DOI: https://doi.org/10.21769/BioProtoc.4057