Wild-type and mutant (G2019S) leucine-rich repeat kinase 2 (LRRK2) associate with subunits of the translocase of outer mitochondrial membrane (TOM) complex.

Leucine-rich repeat kinase 2 (LRRK2) is important in various cellular processes including mitochondrial homeostasis and mutations in this gene lead to Parkinson's disease (PD). However, the full spectrum of LRRK2's functions remain to be elucidated. The translocase of outer mitochondrial membrane (TOM) complex is essential for the import of almost all nuclear-encoded mitochondrial proteins and is fundamental for cellular survival. Using co-immunoprecipitation, super-resolution structured illumination microscopy (SR-SIM), and 3D virtual reality (VR) assisted co-localization analysis techniques we show that wild-type and mutant (G2019S) LRRK2 associate and co-localize with subunits of the TOM complex, either under basal (dimethyl sulfoxide, DMSO) or stress-induced (carbonyl cyanide m-chlorophenyl hydrazine, CCCP) conditions. Interestingly, LRRK2 interacted with TOM40 under both DMSO and CCCP conditions, and when the PD causing mutation, G2019S was introduced, the association was not altered. Moreover, overexpression of G2019S LRRK2 resulted in the formation of large, perinuclear aggregates that co-localized with the TOM complex. Taken together, this is the first study to show that both WT and mutant LRRK2 associate with the TOM complex subunits. These findings provide additional evidence for LRRK2's role in mitochondrial function which has important implications for its role in PD pathogenesis.

Exome sequencing identifies a novel TTC37 mutation in the first reported case of Trichohepatoenteric syndrome (THE-S) in South Africa.

BACKGROUND: Trichohepatoenteric syndrome (THE-S) or phenotypic diarrhoea of infancy is a rare autosomal recessive disorder characterised by severe infantile diarrhoea, facial dysmorphism, immunodeficiency and woolly hair. It was first described in 1982 in two infants with intractable diarrhoea, liver cirrhosis and abnormal hair structure on microscopy. We report on two siblings from a consanguineous family of Somali descent who, despite extensive clinical investigation, remained undiagnosed until their demise. The index patient died of fulminant cytomegalovirus pneumonitis at 3 months of age. METHODS: Whole exome sequencing (WES) was performed on a premortem DNA sample from the index case. Variants in a homozygous recessive state or compound heterozygous state were prioritized as potential candidate variants using TAPER™. Sanger sequencing was done to genotype the parents, unaffected sibling and a deceased sibling for the variant of interest. RESULTS: Exome sequencing identified a novel homozygous mutation (c.4507C > T, rs200067423) in TTC37 which was confirmed by Sanger sequencing in the index case. The identification of this mutation led to the diagnosis of THE-S in the proband and the same homozygous variant was confirmed in a male sibling who died 4 years earlier with severe chronic diarrhoea of infancy. The unaffected parents and sister were heterozygous for the identified variant. CONCLUSIONS: WES permitted definitive genetic diagnosis despite an atypical presentation in the index case and suggests that severe infection, likely secondary to immunodeficiency, may be a presenting feature. In addition definitive molecular diagnosis allows for genetic counseling and future prenatal diagnosis, and demonstrates the value of WES for post-mortem diagnosis of disorders with a non-specific clinical presentation in which a Mendelian cause is suspected.

Underappreciated Roles of the Translocase of the Outer and Inner Mitochondrial Membrane Protein Complexes in Human Disease.

Mitochondria are critical for cellular survival, and for their proper functioning, translocation of ∼1500 proteins across the mitochondrial membranes is required. The translocase of the outer (TOMM) and inner mitochondrial membrane (TIMM) complexes are major components of this translocation machinery. Through specific processes, preproteins and other molecules are imported, translocated, and directed to specific mitochondrial compartments for their function. In this study, we review the association of subunits of these complexes with human disease. Pathogenic mutations have been identified in the TIMM8A (DDP) and DNAJC19 (TIMM14) genes and are linked to Mohr-Tranebjærg syndrome and dilated cardiomyopathy syndrome (with and without ataxia), respectively. Polymorphisms in TOMM40 have been associated with Alzheimer's disease, frontotemporal lobar degeneration, Parkinson's disease with dementia, dementia with Lewy bodies, nonpathological cognitive aging, and various cardiovascular-related traits. Furthermore, reduced protein expression levels of several complex subunits have been associated with Parkinson's disease, Meniere's disease, and cardiovascular disorders. However, increased mRNA and protein levels of complex subunits are found in cancers. This review highlights the importance of the mitochondrial import machinery in human disease and stresses the need for further studies. Ultimately, this knowledge may prove to be critical for the development of therapeutic modalities for these conditions.

Filamin C: a novel component of the KCNE2 interactome during hypoxia.

AIM: KCNE2 encodes for the potassium voltage-gated channel, KCNE2. Mutations in KCNE2 have been associated with long-QT syndrome (LQTS). While KCNE2 has been extensively studied, the functions of its C-terminal domain remain inadequately described. Here, we aimed to elucidate the functions of this domain by identifying its protein interactors using yeast two-hybrid analysis. METHODS: The C-terminal domain of KCNE2 was used as bait to screen a human cardiac cDNA library for putative interacting proteins. Co-localisation and co-immunoprecipitation analyses were used for verification. RESULTS: Filamin C (FLNC) was identified as a putative interactor with KCNE2. FLNC and KCNE2 co-localised within the cell, however, a physical interaction was only observed under hypoxic conditions. CONCLUSION: The identification of FLNC as a novel KCNE2 ligand not only enhances current understanding of ion channel function and regulation, but also provides valuable information about possible pathways likely to be involved in LQTS pathogenesis.