Dissecting the membrane-microtubule sensor in grapevine defence

Specific populations of plant microtubules cooperate with the plasma membrane to sense and process abiotic stress signals, such as cold stress. The current study derived from the question, to what extent this perception system is active in biotic stress signalling. The experimental system consisted of grapevine cell lines, where microtubules or actin filaments are visualised by GFP, such that their response became visible in vivo. We used the bacterial elicitors harpin (inducing cell-death related defence), or flg22 (inducing basal immunity) in combination with modulators of membrane fluidity, or microtubules. We show that DMSO, a membrane rigidifier, can cause microtubule bundling and trigger defence responses, including activation of phytoalexin transcripts. However, DMSO inhibited the gene expression in response to harpin, while promoting the gene expression in response to flg22. Treatment with DMSO also rendered microtubules more persistent to harpin. Paradoxically, Benzylalcohol (BA), a membrane fluidiser, acted in the same way as DMSO. Neither GdCl3, nor diphenylene iodonium were able to block the inhibitory effect of membrane rigidification on harpin-induced gene expression. Treatment with taxol stabilised microtubule against harpin but amplified the response of PAL transcripts. Therefore, the data support implications of a model that deploys specific responses to pathogen-derived signals

Evolutionarily conserved long-chain Acyl-CoA synthetases regulate membrane composition and fluidity

The human AdipoR1 and AdipoR2 proteins, as well as their C. elegans homolog PAQR-2, protect against cell membrane rigidification by exogenous saturated fatty acids by regulating phospholipid composition. Here, we show that mutations in the C. elegans gene acs-13 help to suppress the phenotypes of paqr-2 mutant worms, including their characteristic membrane fluidity defects. acs-13 encodes a homolog of the human acyl-CoA synthetase ACSL1, and localizes to the mitochondrial membrane where it likely activates long chains fatty acids for import and degradation. Using siRNA combined with lipidomics and membrane fluidity assays (FRAP and Laurdan dye staining) we further show that the human ACSL1 potentiates lipotoxicity by the saturated fatty acid palmitate: silencing ACSL1 protects against the membrane rigidifying effects of palmitate and acts as a suppressor of AdipoR2 knockdown, thus echoing the C. elegans findings. We conclude that acs-13 mutations in C. elegans and ACSL1 knockdown in human cells prevent lipotoxicity by promoting increased levels of polyunsaturated fatty acid-containing phospholipids.Peer reviewe

Impairment of the erythrocyte membrane fluidity in survivors of acute myocardial infarction : a prospective study

© 1999 – IOS Press. All rights reservedErythrocytes have to constantly adapt themselves to the varying circulatory system shear stress forces and capillaries diameter. Membrane lipid and protein content have an important role in determining the erythrocyte shape and are main determinants of the membrane solid and fluid behavior which enables the erythrocyte to respond to the outer environment modifications. Membrane fluidity is an inverse index of membrane microviscosity. The aim of the present work is to evaluate prospectively in three periods of time (discharge, after 6 months and one year later) in survivors of an acute myocardial infarction (AMI) the erythrocyte membrane fluidity (outer and inner bilayer) and establish a relation with the cardiovascular events or need of coronary revascularization during a two year clinical follow up. Sixty survivors of acute myocardial infarction were recruited during 1994–96 and were prospectively studied in three periods (discharge, 6 months and after one year), and were compared with a control group (n = 36). Membrane lipid fluidity was determined by means of fluorescence polarization with two probes: 1,6-diphenyl-1,2,5-hexatriene (DPH) and 1,4-trimethylamine 6-phenyl hexa-1,3,5-triene (TMA-DPH), for the characterisation of the hydrophobic and external polar region, respectively. The hydrophobic region was more rigidified (p < 0:01) in the erythrocytes from AMI patients, in relation to the control group. During the time of the study there was a progressive erythrocyte membrane rigidification (DPH p < 0:001; TMA-DPH p < 0:001). We found no relation between erythrocyte membrane fluidity and the coronary risk factors, cardiovascular events or the need of coronary revascularization during the clinical follow-up. In conclusion, after the myocardial infarction erythrocyte membrane of AMI survivors becomes more rigid with time, which could contribute to the decreased erythrocyte deformability and the increased blood viscosity previously described in this group of patients

Membrane Microviscosity Modulates Μ-Opioid Receptor Conformational Transitions and Agonist Efficacy

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66282/1/j.1471-4159.1999.0730289.x.pd

MreB dependent cell envelope homeostasis in Bacillus subtilis

PhD ThesisOne of the hallmarks of cellular life is the protective membrane. The membrane not only encapsulates the nutrient rich cytoplasm, but also facilitates many important processes essential for most biological life such as the ATP producing oxidative phosphorylation, meaning that tight regulation of membrane homeostasis must be sustained. In Bacteria the membrane is also home to the final stages of peptidoglycan synthesis, thus coupling cell wall production and the membrane. The protein governing where the insertion of new peptidoglycan occurs in rod-shaped Bacteria is the actin homologue MreB (Errington, 2015). Previous studies have suggested that MreB and its homologues are involved in cell envelope homeostasis, not only through fatty acid adaptations, but through regulation of peptidoglycan degrading autolysins as well (Dominguez-Cuevas et al., 2013; Strahl et al., 2014). In this thesis I aimed to describe which homeostatic changes occur within the membrane when deleting the MreB cytoskeleton, as well as describe if these changes alter the physical parameters associated with fluidity and temperature dependent growth phenotypes. Additionally, I wanted to elucidate if the deletion of mreB and its homologues changes the sequence of actions following disruptions to membrane homeostasis such as dissipation of membrane potential, which under normal circumstances rigidifies the membrane, delocalizes multiple membrane associated proteins, and eventually induces lysis (Strahl and Hamoen, 2010). Through fatty acid analysis in multiple MreB cytoskeletal mutants I found that the lack of MreB and its homologues lead to altered fatty acid composition, which in turn causes membrane fluidity to be altered in a complex manner, indicating that MreB is important in maintaining a well-coordinated membrane homeostasis. Additionally, I examined membrane rigidification caused by membrane depolarization, and discovered that MreB was not involved, but rather electrostriction was the most likely candidate. Finally, through lysis assays and microscopy I examined membrane depolarization induced lysis. I found that the lysis is caused by MreB being delocalized, thus redirecting the cell wall synthesis machinery and mis-regulating autolysins essential for efficient membrane elongation, finally causing loss of communication between anabolism and catabolism of the cell wall. Together, these findings elucidate the important role MreB occupies in the membrane, not only guiding the cell elongasome, but in maintaining well-coordinated membrane homeostasis

Novel African trypanocidal agents: membrane rigidifying peptides

The bloodstream developmental forms of pathogenic African trypanosomes are uniquely susceptible to killing by small hydrophobic peptides. Trypanocidal activity is conferred by peptide hydrophobicity and charge distribution and results from increased rigidity of the plasma membrane. Structural analysis of lipid-associated peptide suggests a mechanism of phospholipid clamping in which an internal hydrophobic bulge anchors the peptide in the membrane and positively charged moieties at the termini coordinate phosphates of the polar lipid headgroups. This mechanism reveals a necessary phenotype in bloodstream form African trypanosomes, high membrane fluidity, and we suggest that targeting the plasma membrane lipid bilayer as a whole may be a novel strategy for the development of new pharmaceutical agents. Additionally, the peptides we have described may be valuable tools for probing the biosynthetic machinery responsible for the unique composition and characteristics of African trypanosome plasma membranes

Estimating CO2/N2 permselectivity through Si/Al = 5 small-pore zeolites/PTMSP mixed matrix membranes: influence of temperature and topology

In the present work, the effect of zeolite type and topology on CO2 and N2 permeability using zeolites of different topology (CHA, RHO, and LTA) in the same Si/Al = 5, embedded in poly(trimethylsilyl-1-propyne) (PTMSP) is evaluated with temperature. Several models are compared on the prediction of CO2/N2 separation performance and then the modified Maxwell models are selected. The CO2 and N2 permeabilities through these membranes are predicted with an average absolute relative error (AARE) lower than 0.6% taking into account the temperature and zeolite loading and topology on non-idealities such as membrane rigidification, zeolite-polymer compatibility and sieve pore blockage. The evolution of this structure-performance relationship with temperature has also been predicted.The authors gratefully acknowledge the financial support of the Spanish MINECO—General Secretariat for Research, Development and Innovation under project CTQ2016-76231-C2-1-R at the University of Cantabria, and MAT2015-71842-P, at the Instituto de Tecnología Química

Conjugated linoleic acid reduces permeability and fluidity of adipose plasma membranes from obese Zucker rats

NOTICE: this is the author’s version of a work that was accepted for publication in Biochemical and Biophysical Research Communications. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Biochemical and Biophysical Research Communications. July 2010; 398 (2): 199-204.Conjugated linoleic acid (CLA) is a dietary fatty acid frequently used as a body fat reducing agent whose effects upon cell membranes and cellular function remain unknown. Obese Zucker rats were fed atherogenic diets containing saturated fats of vegetable or animal origin with or without 1% CLA, as a mixture of cis(c)9,trans(t)11 and t10,c12 isomers. Plasma membrane vesicles obtained from visceral adi- pose tissue were used to assess the effectiveness of dietary fat and CLA membrane incorporation and its outcome on fluidity and permeability to water and glycerol. A significant decrease in adipose membrane fluidity was correlated with the changes observed in permeability, which seem to be caused by the incor- poration of the t10,c12 CLA isomer into membrane phospholipids. These results indicate that CLA supple- mentation in obese Zucker rats fed saturated and cholesterol rich diets reduces the fluidity and permeability of adipose membranes, therefore not supporting CLA as a body fat reducing agent through membrane fluidification in obese fat consumers