The existence of non-axisymmetric bilayer vesicle shapes predicted by the bilayer couple model

1993 ◽  
Vol 22 (2) ◽  
pp. 97-103 ◽  
Author(s):  
Vera Kralj-Iglič ◽  
Saša Svetina ◽  
Boštjan Žekš
Keyword(s):  
Couple Model ◽  
Vesicle Shapes ◽  
Bilayer Couple ◽  
Bilayer Vesicle

scholarly journals A Bilayer-Couple Model of Bacterial Outer Membrane Vesicle Biogenesis

mBio ◽  
2012 ◽  
Vol 3 (2) ◽  
Author(s):  
Jeffrey W. Schertzer ◽  
Marvin Whiteley
Keyword(s):  
Outer Membrane ◽  
Membrane Vesicle ◽  
Membrane Curvature ◽  
Couple Model ◽  
Gram Negative Bacteria ◽  
Outer Membrane Vesicle ◽  
Gram Negative ◽  
Content Type ◽  
Outer Leaflet ◽  
Bilayer Couple

ABSTRACTGram-negative bacteria naturally produce outer membrane vesicles (OMVs) that arise through bulging and pinching off of the outer membrane. OMVs have several biological functions for bacteria, most notably as trafficking vehicles for toxins, antimicrobials, and signaling molecules. While their biological roles are now appreciated, the mechanism of OMV formation has not been fully elucidated. We recently demonstrated that the signaling molecule 2-heptyl-3-hydroxy-4-quinolone (PQS) is required for OMV biogenesis inP. aeruginosa. We hypothesized that PQS stimulates OMV formation through direct interaction with the outer leaflet of the outer membrane. To test this hypothesis, we employed a red blood cell (RBC) model that has been used extensively to study small-molecule–membrane interactions. Our results revealed that addition of PQS to RBCs induced membrane curvature, resulting in the formation of membrane spicules (spikes), consistent with small molecules that are inserted stably into the outer leaflet of the membrane. Radiotracer experiments demonstrated that sufficient PQS was inserted into the membrane to account for this curvature and that curvature induction was specific to PQS structure. These data suggest that a low rate of interleaflet flip-flop forces PQS to accumulate in and expand the outer leaflet relative to the inner leaflet, thus inducing membrane curvature. In support of PQS-mediated outer leaflet expansion, the PQS effect was antagonized by chlorpromazine, a molecule known to be preferentially inserted into the inner leaflet. Based on these data, we propose a bilayer-couple model to describeP. aeruginosaOMV biogenesis and suggest that this is a general mechanism for bacterial OMV formation.IMPORTANCEDespite the ubiquity and importance of outer membrane vesicle (OMV) production in Gram-negative bacteria, the molecular details of OMV biogenesis are not fully understood. Early experiments showed that 2-heptyl-3-hydroxy-4-quinolone (PQS) induces OMV formation through physical interaction with the membrane but did not elucidate the mechanism. The present study demonstrates that PQS specifically and reversibly promotes blebbing of model membranes dependent upon the same properties that are required for OMV formation inP. aeruginosa. These results are consistent with a mechanism where expansion of the outer leaflet relative to the inner leaflet induces localized membrane curvature. This “bilayer-couple” model can account for OMV formation under all conditions and is easily generalized to other Gram-negative bacteria. The model therefore raises the possibility of a universal paradigm for vesicle production in prokaryotes with features strikingly different from what is known in eukaryotes.

scholarly journals Membrane Distribution of the Pseudomonas Quinolone Signal Modulates Outer Membrane Vesicle Production in Pseudomonas aeruginosa

mBio ◽  
2017 ◽  
Vol 8 (4) ◽  
Author(s):  
Catalina Florez ◽  
Julie E. Raab ◽  
Adam C. Cooke ◽  
Jeffrey W. Schertzer
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Outer Membrane ◽  
Small Molecule ◽  
Membrane Vesicle ◽  
Membrane Vesicles ◽  
Membrane Curvature ◽  
Outer Membrane Vesicles ◽  
Couple Model ◽  
Clinical Strains ◽  
Bilayer Couple

ABSTRACT The Pseudomonas quinolone signal (PQS) is an important quorum-sensing molecule in Pseudomonas aeruginosa that also mediates its own packaging and transport by stimulating outer membrane vesicle (OMV) formation. Because OMVs have been implicated in many virulence-associated behaviors, it is critical that we understand how they are formed. Our group proposed the bilayer-couple model for OMV biogenesis, where PQS intercalates into the outer membrane, causing expansion of the outer leaflet and consequently inducing curvature. In accordance with the model, we hypothesized that PQS must be transported from the cytoplasm to the outer membrane before it can initiate OMV formation. We initially examined two laboratory strains of P. aeruginosa and found significant strain-dependent differences. PQS export correlated strongly with OMV production, even though equivalent amounts of total PQS were produced by both strains. Interestingly, we discovered that poor OMV producers sequestered the majority of PQS in the inner membrane, which appeared to be the result of early saturation of the export pathway. Further analysis showed that strain-specific PQS export and OMV biogenesis patterns were stable once established but could be significantly altered by changing the growth medium. Finally, we demonstrated that the associations described for laboratory strains also held for three clinical strains. These results suggest that factors controlling the export of PQS dictate OMV biogenesis. This work provides new insight into PQS-controlled virulence in P. aeruginosa and provides important tools to further study signal export and OMV biogenesis. IMPORTANCE Bacterial secretion has been recognized as an essential facet of microbial pathogenesis and human disease. Numerous virulence factors have been found to be transported within outer membrane vesicles (OMVs), and delivery using these biological nanoparticles often results in increased potency. OMV biogenesis is an important but poorly understood process that is ubiquitous among Gram-negative organisms. Our group seeks to understand the biochemical mechanisms behind the formation of OMVs and has developed a model of small-molecule-induced membrane curvature as an important driver of this process. With this work, we demonstrate that PQS, a known small-molecule OMV inducer, must be exported to promote OMV biogenesis in both lab-adapted and clinical strains of Pseudomonas aeruginosa. In supporting and expanding the bilayer-couple model of OMV biogenesis, the current work lays the groundwork for studying environmental and genetic factors that modulate OMV production and, consequently, the packaging and delivery of many bacterial factors. IMPORTANCE Bacterial secretion has been recognized as an essential facet of microbial pathogenesis and human disease. Numerous virulence factors have been found to be transported within outer membrane vesicles (OMVs), and delivery using these biological nanoparticles often results in increased potency. OMV biogenesis is an important but poorly understood process that is ubiquitous among Gram-negative organisms. Our group seeks to understand the biochemical mechanisms behind the formation of OMVs and has developed a model of small-molecule-induced membrane curvature as an important driver of this process. With this work, we demonstrate that PQS, a known small-molecule OMV inducer, must be exported to promote OMV biogenesis in both lab-adapted and clinical strains of Pseudomonas aeruginosa. In supporting and expanding the bilayer-couple model of OMV biogenesis, the current work lays the groundwork for studying environmental and genetic factors that modulate OMV production and, consequently, the packaging and delivery of many bacterial factors.

Nearly spherical vesicle shapes calculated by use of spherical harmonics : axisymmetric and nonaxisymmetric shapes and their stability

1992 ◽  
Vol 2 (5) ◽  
pp. 1081-1108 ◽  
Author(s):  
V. Heinrich ◽  
M. Brumen ◽  
R. Heinrich ◽  
S. Svetina ◽  
B. Žekš
Keyword(s):  
Spherical Harmonics ◽  
Spherical Vesicle ◽  
Vesicle Shapes

The S-wave project for focal mechanism studies, earthquakes of 1963

1966 ◽  
Vol 56 (6) ◽  
pp. 1363-1371 ◽  
Author(s):  
William Stauder ◽  
G. A. Bollinger
Keyword(s):  
Point Source ◽  
Focal Mechanism ◽  
Computer Method ◽  
Couple Model ◽  
S Wave ◽  
Wave Data ◽  
Kurile Islands ◽  
Equivalent Point ◽  
Double Couple

Abstract P- and S-wave data for thirty-five earthquakes selected from among the larger earthquakes of 1963 have been investigated. Focal mechanism determinations for twenty-six of these shocks are here presented. The solutions are based upon a combination of a graphical and a computer method for determining the poles of the nodal planes. In all cases it has been found that the mechanism may be adequately represented by a double couple as an equivalent point source of the focus, although in some few instances a single couple cannot be excluded as a possible alternate interpretation. The solution of a mid-Atlantic earthquake of November 17, 1963 is presented as an example of a focus which clearly conforms to the double couple model. Special attention is called to the solutions for a series of earthquakes in the Kurile Islands, and to three earthquakes of the mid-Atlantic.

scholarly journals Relating vesicle shapes in pyroclasts to eruption styles

2013 ◽  
Vol 75 (2) ◽  
Author(s):  
Pranabendu Moitra ◽  
Helge M. Gonnermann ◽  
Bruce F. Houghton ◽  
Thomas Giachetti
Keyword(s):  
Vesicle Shapes
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