An ubiquitous and conserved proteolytic system regulates the stability of mitochondrial inner membrane proteins. Two AAA proteases with catalytic sites at opposite membrane surfaces form a membrane-integrated quality control system and exert crucial functions during the biogenesis of mitochondria. Their activity is modulated by another membrane-protein complex that is composed of prohibitins. Peptides generated upon proteolysis in the matrix space are transported across the inner membrane by an ATP-binding cassette transporter. The function of these conserved components is discussed in the present review.
Eukaryotic AAA proteases form a conserved family of membrane-embedded ATP-dependent proteases but have been analyzed functionally only in the yeast Saccharomyces cerevisiae. Here, we have identified two novel members of this protein family in the filamentous fungus Neurospora crassa, which were termed MAP-1 and IAP-1. Both proteins are localized to the inner membrane of mitochondria. They are part of two similar-sized high molecular mass complexes, but expose their catalytic sites to opposite membrane surfaces, namely, the intermembrane and the matrix space. Disruption of iap-1 by repeat-induced point mutation caused a slow growth phenotype at high temperature and stabilization of a misfolded inner membrane protein against degradation. IAP-1 could partially substitute for functions of its yeast homolog Yme1, demonstrating functional conservation. However, respiratory growth at 37 degrees C was not restored. Our results identify two components of the quality control system of the mitochondrial inner membrane in N. crassa and suggest that AAA proteases with catalytic sites exposed to opposite membrane surfaces are present in mitochondria of all eukaryotic cells.
Tcm62p, distantly related to chaperonins, is required for the assembly of succinate dehydrogenase in mitochondria of Saccharomyces cerevisiae and was proposed to exert chaperone activity. We demonstrate here crucial functions of Tcm62p under heat stress. It ensures mitochondrial gene expression at elevated temperatures and prevents heat-aggregation of the ribosomal subunit Var1p. Similar to chaperonins, Tcm62p forms a high molecular mass protein complex of approximately 850 kDa in the mitochondrial matrix space. These results suggest a more general chaperone function of Tcm62p in mitochondria.z 2000 Federation of European Biochemical Societies.
Please refer to abstract number 4. This abstract was originally submitted as a poster, and on the basis of its scientific interest and merit, was chosen by the colloquium organisers to be presented as an oral communication, as well as a poster subunit 111 of cytochrome oxidase affecting the complex B12 Mitochondria1 AAA proteases: Control of biogenesis and maintenance of respiratory chain complexes
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.