Parallel activation in the ATP supply-demand system lessens the impact of inborn enzyme deficiencies, inhibitors, poisons or substrate shortage on oxidative phosphorylation in vivo

A potential kinetic impact of parallel activation of different steps during an increased energy demand on the effect of inborn enzyme deficiencies, physiological inhibitors, external poisons and substrate shortage on oxidative phosphorylation was studied in the theoretical way. Numerical simulations were performed with the aid of the previously developed computer model of oxidative phosphorylation. It was demonstrated that the parallel activation mechanism diminishes significantly changes in fluxes and metabolite concentrations occurring at a given degree of inactivation of the system by one of the above-mentioned factors. It was also shown that parallel activation decreases greatly the threshold value of the relative activity of oxidative phosphorylation, below which the oxygen consumption flux and ATP turnover flux become significantly affected. Finally, computer simulations predicted that parallel activation leads to a considerable increase in the apparent affinity of oxidative phosphorylation to oxygen, which delays the effect of inhibitors and poisons competing with oxygen for the active centre of cytochrome oxidase. It is concluded that one of possible functions of parallel direct activation of different steps of oxidative phosphorylation is to increase the resistance of the system to a decrease in the concentration/activity of different oxidative phosphorylation complexes.     

Mitochondrial genome content is regulated during nematode development

Growth and development rely on the mitochondrial respiratory chain (MRC) as the major source of ATP. We measured the mitochondrial DNA (mtDNA) copy number of each of the Caenorhabditis elegans developmental stages. Embryos, L1, L2, and L3 larvae all have approximately 25,000 copies of maternally derived mtDNA. The copy number increases fivefold in L4 larvae and a further sixfold in adult hermaphrodites, but only twofold in adult males. The majority of mtDNA in adult worms is germline associated, and germline-deficient mutants show markedly reduced mtDNA contents. With sperm-deficient or oocyte-deficient mutants, we confirm that mtDNA amplification is primarily associated with oocyte production. When mtDNA replication is inhibited, a quantitative and homogeneous arrest as L3 larvae occurs. Thus, mtDNA amplification is a necessary component of normal development and its regulation may involve an energy-sensing decision or checkpoint that can be invoked when mitochondrial energy generation is impaired.     

Cellular localisation of a water-soluble fullerene derivative

Fullerenes are a new class of compounds with potential uses in biology and medicine and many insights were made in the knowledge of their interaction with various biological systems. However, their interaction with organised living systems as well as the site of their potential action remains unclear. In this work, we have demonstrated that a fullerene derivative could cross the external cellular membrane and it localises preferentially to the mitochondria. We propose that our finding supports the potential use of fullerenes as drug delivery agents as their structure mimics that of clathrin known to mediate endocytosis.     

Simulations of membranes and other interfacial systems using P2(1) and Pc periodic boundary conditions

We demonstrate the ease and utility of simulating heterogeneous interfacial systems with P2(1) and Pc periodic boundary conditions which allow, for example, lipids in a membrane to switch leaflets. In preliminary tests, P2(1) was shown to yield equivalent results to P1 in simulations of bulk water, a water/vacuum interface, and pure DPPC bilayers with an equal number of lipids per leaflet; equivalence of Pc and P1 was also demonstrated for the former two systems. P2(1) was further tested in simulations involving the spreading of an octane film on water, and equilibration of a DPPC bilayer from an initial condition containing different numbers of lipids in the two leaflets. Lastly, a simulation in P2(1) of a DOPC/melittin membrane showed significant passage of lipids to the melittin-containing leaflet from the initial distribution, and lends insight into the condensation of lipids by melittin.     

Multi-bead-and-spring model to interpret protein detachment studied by AFM force spectroscopy

This article deals with the detachment of molecules (fibrinogen) from a surface studied experimentally with an atomic force microscope. The detachment (or rupture) forces are measured as a function of the retraction velocity and exhibit a clear dependence on this parameter, even though the interaction between the molecules and the surface are nonspecific. To interpret these data, a mechanical multi-bead-and-spring model is developed. It consists of one to several parallel, "molecular" springs connected to an extra spring representing the cantilever that is moved at constant velocity. The free end of each molecular spring terminates with a particle that interacts with the surface through a Lennard-Jones potential. This Brownian dynamics model is used to analyze the experimental findings. In the framework of this model, it appears that the fibrinogen molecule must be ascribed a stiffness much smaller than that of the cantilever. In addition, several bonds between the molecule and the surface must be taken into account for the range of the molecule-surface interaction not to be unrealistically small. In future work, this model will be extended to more complex mechanisms such as the detachment of cells from a surface.     

The crystallization of biological macromolecules under microgravity: a way to more accurate three-dimensional structures?

The crystallization of proteins and other biological particles (including nucleic acids, nucleo-protein complexes and large assemblies such as nucleosomes, ribosomal subunits or viruses) in a microgravity environment can produce crystals having lesser defects than crystals prepared under normal gravity on earth. Such microgravity-grown crystals can diffract X-rays to a higher resolution and have a lower mosaic spread. The inferred electron density maps can be richer in details owing to which more accurate three-dimensional structure models can be built. Major results reported in this field of research are reviewed. Novel ones obtained with the Advanced Protein Crystallization Facility are presented. For structural biology, practical applications and implications associated with crystallization and crystallography onboard the International Space Station are discussed.     

Astrocytes,cells involved in neuro-immune interactions in the central nervous system

The astrocyte, the major glial cell in the central nervous system, may influence many aspects of inflammation and immune reactivity within the brain. We have established a model of chronically activated T lymphocytes, interacting with neural cells of diverse origin to study the complex immune regulatory system suspected to lead to neuroinflammatory diseases. We show that human astrocytes became reactive following T cell contact, secreting proinflammatory cytokines, matrix metalloproteinases (MMP) and tissue inhibitors of metalloproteinase (TIMP). The altered MMP/TIMP system was shown to be involved in deleterious effects displayed by activated T cells towards human multipotent neural precursers by controlling their sensitivity to T cell-induced Fas-mediated apoptosis. MMP/TIMP was suspected to stabilize Fas at the cell membrane. In a model of mixed rat glial cells in primary culture (astrocytes, oligodendrocytes), activated T lymphocytes induced the collapse of processes and the death of immature oligodendrocytes. These effects were associated with upregulation of Fas at the cell surface of oligodendrocytes and secretion of MMP and TIMP by astrocytes. By amplifying the expression of inflammatory molecules including the MMP/TIMP system, astrocytes appear to be a crucial relay in the deleterious molecular cascade triggered by activated T lymphocytes. Detection of altered MMP/TIMP in patients suffering from myelopathy associated with retroviral infection (HTLV-1) strongly suggests its involvement in the physiopathological process of the disease.     

Hair cycle dynamics: the case of the human hair follicle

The existence of a growth and regeneration cycle makes the hair follicle a true paradigm of tissue homeostasis. Analysis of about 9000 cycles led us to propose a stochastic model of human hair dynamics. The existence of hair cycles implies that stem cells must be cyclically activated and hair melanin unit has to be renewed. Using different markers, we were able to identify two distinct epithelial stem cell reservoirs, located in the upper and lower thirds of the anagen hair follicle outer root sheath. These two reservoirs fuse during the regression phase and individualize again in the new forming anagen hair follicle. Using a set of antibodies specific of melanocyte lineage and melanogenesis, pigmentation unit turnover was followed throughout the entire hair cycle. In the terminal anagen hair, active melanocytes were localized on top of the dermal papilla, while amelanotic melanocytes were identified in the upper third of the outer root sheath (ORS). Those amelanotic melanocytes located in upper ORS probably represented a melanocyte reservoir for successive hair generation, since at the induction of anagen phase, some melanocytes were committed to cell division and melanogenesis was turned on, but only in the nascent hair bulb, close to the dermal papilla.