The Design and Structure of Outer Membrane Receptors from Peroxisomes, Mitochondria, and Chloroplasts

Molecular characterization, targeting and expression analysis of chloroplast and mitochondrion protein import components in Nicotiana benthamiana

Improved bioinformatics tools for annotating gene function are becoming increasingly available, but such information must be considered theoretical until further experimental evidence proves it. In the work reported here, the genes for the main components of the translocons of the outer membrane of chloroplasts (Toc) and mitochondria (Tom), including preprotein receptors and protein-conducting channels of N. benthamiana, were identified. Sequence identity searches and phylogenetic relationships with functionally annotated sequences such as those of A. thaliana revealed that N. benthamiana orthologs mainly exist as recently duplicated loci. Only a Toc34 ortholog was found (NbToc34), while Toc159 receptor family was composed of four orthologs but somewhat different from those of A. thaliana. Except for NbToc90, the rest (NbToc120, NbToc159A and NbToc159B) had a molecular weight of about 150 kDa and an acidic domain similar in length. Only two orthologs of the Tom20 receptors, NbTom20-1 and NbTom20-2, were found. The number of the Toc and Tom receptor isoforms in N. benthamiana was comparable to that previously reported in tomato and what we found in BLAST searches in other species in the genera Nicotiana and Solanum. After cloning, the subcellular localization of N. benthamiana orthologs was studied, resulting to be identical to that of A. thaliana receptors. Phenotype analysis after silencing together with relative expression analysis in roots, stems and leaves revealed that, except for the Toc and Tom channel-forming components (NbToc75 and NbTom40) and NbToc34, functional redundancy could be observed either among Toc159 or mitochondrial receptors. Finally, heterodimer formation between NbToc34 and the NbToc159 family receptors was confirmed by two alternative techniques indicating that different Toc complexes could be assembled. Additional work needs to be addressed to know if this results in a functional specialization of each Toc complex.

Bnip3 in mitophagy: Novel insights and potential therapeutic target for diseases of secondary mitochondrial dysfunction

The present review is a summary of the recent literature concerning Bnip3 expression, function, and regulation, along with its implications in mitochondrial dysfunction, disorders of mitophagy homeostasis, and development of diseases of secondary mitochondrial dysfunction. As a member of the Bcl-2 family of cell death-regulating factors, Bnip3 mediates mPTP opening, mitochondrial potential, oxidative stress, calcium overload, mitochondrial respiratory collapse, and ATP shortage of mitochondria from multiple cells. Recent studies have discovered that Bnip3 regulates mitochondrial dysfunction, mitochondrial fragmentation, mitophagy, cell apoptosis, and the development of lipid disorder diseases via numerous cellular signaling pathways. In addition, Bnip3 promotes the development of cardiac hypertrophy by mediating inflammatory response or the related signaling pathways of cardiomyocytes and is also responsible for raising abnormal mitophagy and apoptosis progression through multiple molecular signaling pathways, inducing the pathogenesis and progress of hepatocellular carcinoma (HCC). Different molecules regulate Bnip3 expression at both the transcriptional and post-transcriptional level, leading to mitochondrial dysfunction and unbalance of mitophagy in hepatocytes, which promotes the development of non-alcoholic fatty liver disease (NAFLD). Thus, Bnip3 plays an important role in mitochondrial dysfunction and mitophagy homeostasis and has emerged as a promising therapeutic target for diseases of secondary mitochondrial dysfunction.