2,526 research outputs found
Translocation and insertion of precursor proteins into isolated outer membranes of mitochondria
Nuclear-encoded proteins destined for mitochondria must cross the outer or both outer and inner membranes to reach their final sub- mitochondrial locations. While the inner membrane can translocate preproteins by itself, it is not known whether the outer membrane also contains an endogenous protein translocation activity which can function independently of the inner membrane. To selectively study the protein transport into and across the outer membrane of Neurospora crassa mitochondria, outer membrane vesicles were isolated which were sealed, in a right-side-out orientation, and virtually free of inner membranes. The vesicles were functional in the insertion and assembly of various outer membrane proteins such as porin, MOM19, and MOM22. Like with intact mitochondria, import into isolated outer membranes was dependent on protease-sensitive surface receptors and led to correct folding and membrane integration. The vesicles were also capable of importing a peripheral component of the inner membrane, cytochrome c heme lyase (CCHL), in a receptor-dependent fashion. Thus, the protein translocation machinery of the outer mitochondrial membrane can function as an independent entity which recognizes, inserts, and translocates mitochondrial preproteins of the outer membrane and the intermembrane space. In contrast, proteins which have to be translocated into or across the inner membrane were only specifically bound to the vesicles, but not imported. This suggests that transport of such proteins involves the participation of components of the intermembrane space and/or the inner membrane, and that in these cases the outer membrane translocation machinery has to act in concert with that of the inner membrane
New and revised parameters for several southern OB binaries
Using ESO FEROS archive spectra of several southern OB-type binaries, we
derived periods for three SB2 spectroscopic binaries, HD 97166, HD 115455, and
HD 123590, and two SB1 systems, HD 130298 and HD 163892. It was also possible
to use new FEROS spectra to improve the parameters of the known binaries, KX
Vel and HD 167263. For KX Vel, we determined a dynamic mass of the primary of
16.8 M, while the evolutionary model suggests a higher value of 20.2
M. We derived an improved period for HD 167263, and in its spectra,
we recognized contributions of both of its interferometric components.Comment: 9 pages, A&A accepte
How a well-adapting immune system remembers
An adaptive agent predicting the future state of an environment must weigh
trust in new observations against prior experiences. In this light, we propose
a view of the adaptive immune system as a dynamic Bayesian machinery that
updates its memory repertoire by balancing evidence from new pathogen
encounters against past experience of infection to predict and prepare for
future threats. This framework links the observed initial rapid increase of the
memory pool early in life followed by a mid-life plateau to the ease of
learning salient features of sparse environments. We also derive a modulated
memory pool update rule in agreement with current vaccine response experiments.
Our results suggest that pathogenic environments are sparse and that memory
repertoires significantly decrease infection costs even with moderate sampling.
The predicted optimal update scheme maps onto commonly considered competitive
dynamics for antigen receptors
Regulation of T cell expansion by antigen presentation dynamics
An essential feature of the adaptive immune system is the proliferation of
antigen-specific lymphocytes during an immune reaction to form a large pool of
effector cells. This proliferation must be regulated to ensure an effective
response to infection while avoiding immunopathology. Recent experiments in
mice have demonstrated that the expansion of a specific clone of T cells in
response to cognate antigen obeys a striking inverse power law with respect to
the initial number of T cells. Here, we show that such a relationship arises
naturally from a model in which T cell expansion is limited by decaying levels
of presented antigen. The same model also accounts for the observed dependence
of T cell expansion on affinity for antigen and on the kinetics of antigen
administration. Extending the model to address expansion of multiple T cell
clones competing for antigen, we find that higher affinity clones can suppress
the proliferation of lower affinity clones, thereby promoting the specificity
of the response. Employing the model to derive optimal vaccination protocols,
we find that exponentially increasing antigen doses can achieve a nearly
optimized response. We thus conclude that the dynamics of presented antigen is
a key regulator of both the size and specificity of the adaptive immune
response
Effect of sample preparation on the thermal degradation of metal-added biomass
The present study investigates the effect of different sample preparation methods on the pyrolysis behaviour of metal-added biomass; Willow samples were compared in the presence of two salts of zinc and lead containing sulphate and nitrate anions which were added to the wood samples with three different techniques as dry-mixing, impregnation and ion-exchange. The effect of acid and water wash as common demineralisation pre-treatments were also analysed to evaluate their roles in the thermal degradation of the biomass. Results from thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR) and pyrolysis-mass spectrometry (Py-MS) measurements indicated that these pre-treatments change the matrix and the physical-chemical properties of wood. Results suggested that these structural changes increase the thermal stability of cellulose during pyrolysis. Sample preparation was also found to be a crucial factor during pyrolysis; different anions of metal salts changed the weight loss rate curves of wood material, which indicates changes in the primary degradation process of the biomass. Results also showed that dry-mixing, impregnation or ion-exchange influence the thermal behaviour of wood in different ways when a chosen metal salt was and added to the wood material
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