Inner membrane

About: Inner membrane is a research topic. Over the lifetime, 3780 publications have been published within this topic receiving 220481 citations.

Enzymatic properties of the inner and outer membranes of rat liver mitochondria

Abstract: Treatment of rat liver mitochondria with digitonin followed by differential centrifugation was used to resolve the intramitochondrial localization of both soluble and particulate enzymes. Rat liver mitochondria were separated into three fractions: inner membrane plus matrix, outer membrane, and a soluble fraction containing enzymes localized between the membranes plus some solublized outer membrane. Monoamine oxidase, kynurenine hydroxylase, and rotenone-insensitive NADH-cytochrome c reductase were found primarily in the outer membrane fraction. Succinate-cytochrome c reductase, succinate dehydrogenase, cytochrome oxidase, beta-hydroxybutyrate dehydrogenase, alpha-ketoglutarate dehydrogenase, lipoamide dehydrogenase, NAD- and NADH-isocitrate dehydrogenase, glutamate dehydrogenase, aspartate aminotransferase, and ornithine transcarbamoylase were found in the inner membrane-matrix fraction. Nucleoside diphosphokinase was found in both the outer membrane and soluble fractions; this suggests a dual localization. Adenylate kinase was found entirely in the soluble fraction and was released at a lower digitonin concentration than was the outer membrane; this suggests that this enzyme is localized between the two membranes. The inner membrane-matrix fraction was separated into inner membrane and matrix by treatment with the nonionic detergent Lubrol, and this separation was used as a basis for calculating the relative protein content of the mitochondrial components. The inner membrane-matrix fraction retained a high degree of morphological and biochemical integrity and exhibited a high respiratory rate and respiratory control when assayed in a sucrose-mannitol medium containing EDTA.

Loss of a-Type Lamin Expression Compromises Nuclear Envelope Integrity Leading to Muscular Dystrophy

Abstract: The nuclear lamina is a protein meshwork lining the nucleoplasmic face of the inner nuclear membrane and represents an important determinant of interphase nuclear architecture. Its major components are the A- and B-type lamins. Whereas B-type lamins are found in all mammalian cells, A-type lamin expression is developmentally regulated. In the mouse, A-type lamins do not appear until midway through embryonic development, suggesting that these proteins may be involved in the regulation of terminal differentiation. Here we show that mice lacking A-type lamins develop to term with no overt abnormalities. However, their postnatal growth is severely retarded and is characterized by the appearance of muscular dystrophy. This phenotype is associated with ultrastructural perturbations to the nuclear envelope. These include the mislocalization of emerin, an inner nuclear membrane protein, defects in which are implicated in Emery-Dreifuss muscular dystrophy (EDMD), one of the three major X-linked dystrophies. Mice lacking the A-type lamins exhibit tissue-specific alterations to their nuclear envelope integrity and emerin distribution. In skeletal and cardiac muscles, this is manifest as a dystrophic condition related to EDMD.

Coupling of the nucleus and cytoplasm: Role of the LINC complex

Abstract: The nuclear envelope defines the barrier between the nucleus and cytoplasm and features inner and outer membranes separated by a perinuclear space (PNS). The inner nuclear membrane contains specific integral proteins that include Sun1 and Sun2. Although the outer nuclear membrane (ONM) is continuous with the endoplasmic reticulum, it is nevertheless enriched in several integral membrane proteins, including nesprin 2 Giant (nesp2G), an 800-kD protein featuring an NH2-terminal actin-binding domain. A recent study (Padmakumar, V.C., T. Libotte, W. Lu, H. Zaim, S. Abraham, A.A. Noegel, J. Gotzmann, R. Foisner, and I. Karakesisoglou. 2005. J. Cell Sci. 118:3419–3430) has shown that localization of nesp2G to the ONM is dependent upon an interaction with Sun1. In this study, we confirm and extend these results by demonstrating that both Sun1 and Sun2 contribute to nesp2G localization. Codepletion of both of these proteins in HeLa cells leads to the loss of ONM-associated nesp2G, as does overexpression of the Sun1 lumenal domain. Both treatments result in the expansion of the PNS. These data, together with those of Padmakumar et al. (2005), support a model in which Sun proteins tether nesprins in the ONM via interactions spanning the PNS. In this way, Sun proteins and nesprins form a complex that links the nucleoskeleton and cytoskeleton (the LINC complex).

Lipid a modification systems in gram-negative bacteria

Abstract: The lipid A moiety of lipopolysaccharide forms the outer monolayer of the outer membrane of most gram-negative bacteria. Escherichia coli lipid A is synthesized on the cytoplasmic surface of the inner membrane by a conserved pathway of nine constitutive enzymes. Following attachment of the core oligosaccharide, nascent core-lipid A is flipped to the outer surface of the inner membrane by the ABC transporter MsbA, where the O-antigen polymer is attached. Diverse covalent modifications of the lipid A moiety may occur during its transit from the outer surface of the inner membrane to the outer membrane. Lipid A modification enzymes are reporters for lipopolysaccharide trafficking within the bacterial envelope. Modification systems are variable and often regulated by environmental conditions. Although not required for growth, the modification enzymes modulate virulence of some gram-negative pathogens. Heterologous expression of lipid A modification enzymes may enable the development of new vaccines.

Protein import into mitochondria.

Abstract: Mitochondria import many hundreds of different proteins that are encoded by nuclear genes These proteins are targeted to the mitochondria, translocated through the mitochondrial membranes, and sorted to the different mitochondrial subcompartments Separate translocases in the mitochondrial outer membrane (TOM complex) and in the inner membrane (TIM complex) facilitate recognition of preproteins and transport across the two membranes Factors in the cytosol assist in targeting of preproteins Protein components in the matrix partake in energetically driving translocation in a reaction that depends on the membrane potential and matrix-ATP Molecular chaperones in the matrix exert multiple functions in translocation, sorting, folding, and assembly of newly imported proteins