YidC and SecY mediate membrane insertion of a type I transmembrane domain

YidC has been identified recently as an evolutionary conserved factor that is involved in the integration of inner membrane proteins (IMPs) in Escherichia coli. The discovery of YidC has inspired the reevaluation of membrane protein assembly pathways in E. coli. In this study, we have analyzed the role of YidC in membrane integration of a widely used model IMP, leader peptidase (Lep). Site-directed photocross-linking experiments demonstrate that both YidC and SecY contact nascent Lep very early during biogenesis, at only 50-amino acid nascent chain length. At this length the first transmembrane domain (TM), which acquires a type I topology, is not even fully exposed outside the ribosome. The pattern of interactions appears dependent on the position of the cross-linking probe in the nascent chain. Upon elongation, nascent Lep remains close to YidC and comes into contact with lipids as well. Our results suggest a role for YidC in both the reception and lipid partitioning of type I TMs

Nonequilibrium dynamics of mixtures of active and passive colloidal particles

We develop a mesoscopic field theory for the collective nonequilibrium dynamics of multicomponent mixtures of interacting active (i.e., motile) and passive (i.e., nonmotile) colloidal particles with isometric shape in two spatial dimensions. By a stability analysis of the field theory, we obtain equations for the spinodal that describes the onset of a motility-induced instability leading to cluster formation in such mixtures. The prediction for the spinodal is found to be in good agreement with particle-resolved computer simulations. Furthermore, we show that in active-passive mixtures the spinodal instability can be of two different types. One type is associated with a stationary bifurcation and occurs also in one-component active systems, whereas the other type is associated with a Hopf bifurcation and can occur only in active-passive mixtures. Remarkably, the Hopf bifurcation leads to moving clusters. This explains recent results from simulations of active-passive particle mixtures, where moving clusters and interfaces that are not seen in the corresponding one-component systems have been observed.Comment: 17 pages, 3 figure

Focusing by blocking: repeatedly generating central density peaks in self-propelled particle systems by exploiting diffusive processes

Over the past few years the displacement statistics of self-propelled particles has been intensely studied, revealing their long-time diffusive behavior. Here, we demonstrate that a concerted combination of boundary conditions and switching on and off the self-propelling drive can generate and afterwards arbitrarily often restore a non-stationary centered peak in their spatial distribution. This corresponds to a partial reversibility of their statistical behavior, in opposition to the above-mentioned long-time diffusive nature. Interestingly, it is a diffusive process that mediates and makes possible this procedure. It should be straightforward to verify our predictions in a real experimental system.Comment: 6 pages, 6 figure

Nitric oxide synthase inhibition results in synergistic anti-tumour activity with melphalan and tumour necrosis factor alpha-based isolated limb perfusions

Nitric oxide (NO) is an important molecule in regulating tumour blood flow and stimulating tumour angiogenesis. Inhibition of NO synthase by L-NAME might induce an anti-tumour effect by limiting nutrients and oxygen to reach tumour tissue or affecting vascular growth. The anti-tumour effect of L-NAME after systemic administration was studied in a renal subcapsular CC531 adenocarcinoma model in rats. Moreover, regional administration of L-NAME, in combination with TNF and melphalan, was studied in an isolated limb perfusion (ILP) model using BN175 soft-tissue sarcomas. Systemic treatment with L-NAME inhibited growth of adenocarcinoma significantly but was accompanied by impaired renal function. In ILP, reduced tumour growth was observed when L-NAME was used alone. In combination with TNF or melphalan, L-NAME increased response rates significantly compared to perfusions without L-NAME (0–64% and 0–63% respectively). An additional anti-tumour effect was demonstrated when L-NAME was added to the synergistic combination of melphalan and TNF (responses increased from 70 to 100%). Inhibition of NO synthase reduces tumour growth both after systemic and regional (ILP) treatment. A synergistic anti-tumour effect of L-NAME is observed in combination with melphalan and/or TNF using ILP. These results indicate a possible role of L-NAME for the treatment of solid tumours in a systemic or regional setting. © 2000 Cancer Research Campaig

Lack of efficacy of Doxil® in TNF-α-based isolated limb perfusion in sarcoma-bearing rats

textabstractHere we show that Doxil® has minimal antitumour activity in the isolated limb perfusion (ILP) setting and its activity was not enhanced by the addition of tumour necrosis factor (TNF). Doxil® accumulation in tumour tissue was low and also not augmented by TNF. In contrast, activity of free conventional doxorubicin was enhanced by TNF. We conclude that application of Doxil® in a TNF-based ILP is not a useful alternative to free conventional doxorubicin or melphalan

TNF- α augments intratumoural concentrations of doxorubicin in TNF- α -based isolated limb perfusion in rat sarcoma models and enhances anti-tumour effects

We have shown previously that isolated limb perfusion (ILP) in sarcoma-bearing rats results in high response rates when melphalan is used in combination with tumour necrosis factor alpha (TNF-α). This is in line with observations in patients. Here we show that ILP with doxorubicin in combination with TNF-α has comparable effects in two different rat sarcoma tumour models. The addition of TNF-α exhibits a synergistic anti-tumour effect, resulting in regression of the tumour in 54% and 100% of the cases for the BN175-fibrosarcoma and the ROS-1 osteosarcoma respectively. The combination is shown to be mandatory for optimal tumour response. The effect of high dose TNF-α on the activity of cytotoxic agents in ILP is still unclear. We investigated possible modes by which TNF-α could modulate the activity of doxorubicin. In both tumour models increased accumulation of doxorubicin in tumour tissue was found: 3.1-fold in the BN175 and 1.8-fold in the ROS-1 sarcoma after ILP with doxorubicin combined with TNF-α in comparison with an ILP with doxorubicin alone. This increase in local drug concentration may explain the synergistic anti-tumour responses after ILP with the combination. In vitro TNF-α fails to augment drug uptake in tumour cells or to increase cytotoxicity of the drug. These findings make it unlikely that TNF-α directly modulates the activity of doxorubicin in vivo. As TNF-α by itself has no or only minimal effect on tumour growth, an increase in local concentrations of chemotherapeutic drugs might well be the main mechanism for the synergistic anti-tumour effects. © 2000 Cancer Research Campaig