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Bacterial secretion and the role of diffusive and subdiffusive first passage processes.

Marten F, Tsaneva-Atanasova K, Giuggioli L - PLoS ONE (2012)

Bottom Line: By funneling protein effectors through needle complexes located on the cellular membrane, bacteria are able to infect host cells during type III secretion events.As a result, theoretical predictions of secretion times are still lacking.Here we provide a model that quantifies, depending on the transport characteristics within bacterial cytoplasm, the amount of time for a protein effector to reach either of the available needle complexes.

View Article: PubMed Central - PubMed

Affiliation: Department of Engineering Mathematics, University of Bristol, Bristol, United Kingdom.

ABSTRACT
By funneling protein effectors through needle complexes located on the cellular membrane, bacteria are able to infect host cells during type III secretion events. The spatio-temporal mechanisms through which these events occur are however not fully understood, due in part to the inherent challenges in tracking single molecules moving within an intracellular medium. As a result, theoretical predictions of secretion times are still lacking. Here we provide a model that quantifies, depending on the transport characteristics within bacterial cytoplasm, the amount of time for a protein effector to reach either of the available needle complexes. Using parameters from Shigella flexneri we are able to test the role that translocators might have to activate the needle complexes and offer semi-quantitative explanations of recent experimental observations.

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Related in: MedlinePlus

Placement of targets(red objects) on the boundary of a sphere. In the top left corner of panel (A), a single target is displayed. In the top right and bottom left corner of panel (A) 42 and 92 targets are placed according to a geodesic grid. In the bottom right corner of panel (A), the geodesic grid for 25 targets is used but only to half of the sphere. The fourth panel shows 25 targets on the upper hemisphere – to study localized activation of needle complexes. (B) If we have no information about the starting location of a random walker in a disk, we assume that it is uniformly random within a smaller disk of radius . (C) The same idea applied to a random walker in a sphere; we assume that it can start anywhere within a smaller spherical volume of radius .
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pone-0041421-g008: Placement of targets(red objects) on the boundary of a sphere. In the top left corner of panel (A), a single target is displayed. In the top right and bottom left corner of panel (A) 42 and 92 targets are placed according to a geodesic grid. In the bottom right corner of panel (A), the geodesic grid for 25 targets is used but only to half of the sphere. The fourth panel shows 25 targets on the upper hemisphere – to study localized activation of needle complexes. (B) If we have no information about the starting location of a random walker in a disk, we assume that it is uniformly random within a smaller disk of radius . (C) The same idea applied to a random walker in a sphere; we assume that it can start anywhere within a smaller spherical volume of radius .

Mentions: An effector keeps moving inside the bacterium until it reaches one of the absorbing targets. The targets, representing the intracellular base of the needle complexes in S. flexneri, are modelled as small circular or spherical objects with radius . As the time it takes to move from the base to the tip of the needle complex is considered negligible in our model, the first passage time for an effector to be secreted takes into account only the dynamics to reach the base of a target. The midpoint of these targets is placed exactly on the domain boundary, as shown by the red circular objects in Fig. 8. Electron microscopy imaging studies [25] suggest that needle complexes are distributed over most of the cellular surface. For simplicity we place targets to cover the boundary domain in a uniform way. For the disk we simply choose an equidistant placement (see e.g. Fig. 8B). In 3d it is accomplished by constructing a geodesic grid, that is by distributing initially a subset of the targets as the vertices of an icosahedron tangent with the sphere, adding the additional ones so that they are equidistant between the vertices of the icosahedron and then projecting all the 3d target locations onto the sphere.


Bacterial secretion and the role of diffusive and subdiffusive first passage processes.

Marten F, Tsaneva-Atanasova K, Giuggioli L - PLoS ONE (2012)

Placement of targets(red objects) on the boundary of a sphere. In the top left corner of panel (A), a single target is displayed. In the top right and bottom left corner of panel (A) 42 and 92 targets are placed according to a geodesic grid. In the bottom right corner of panel (A), the geodesic grid for 25 targets is used but only to half of the sphere. The fourth panel shows 25 targets on the upper hemisphere – to study localized activation of needle complexes. (B) If we have no information about the starting location of a random walker in a disk, we assume that it is uniformly random within a smaller disk of radius . (C) The same idea applied to a random walker in a sphere; we assume that it can start anywhere within a smaller spherical volume of radius .
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3412870&req=5

pone-0041421-g008: Placement of targets(red objects) on the boundary of a sphere. In the top left corner of panel (A), a single target is displayed. In the top right and bottom left corner of panel (A) 42 and 92 targets are placed according to a geodesic grid. In the bottom right corner of panel (A), the geodesic grid for 25 targets is used but only to half of the sphere. The fourth panel shows 25 targets on the upper hemisphere – to study localized activation of needle complexes. (B) If we have no information about the starting location of a random walker in a disk, we assume that it is uniformly random within a smaller disk of radius . (C) The same idea applied to a random walker in a sphere; we assume that it can start anywhere within a smaller spherical volume of radius .
Mentions: An effector keeps moving inside the bacterium until it reaches one of the absorbing targets. The targets, representing the intracellular base of the needle complexes in S. flexneri, are modelled as small circular or spherical objects with radius . As the time it takes to move from the base to the tip of the needle complex is considered negligible in our model, the first passage time for an effector to be secreted takes into account only the dynamics to reach the base of a target. The midpoint of these targets is placed exactly on the domain boundary, as shown by the red circular objects in Fig. 8. Electron microscopy imaging studies [25] suggest that needle complexes are distributed over most of the cellular surface. For simplicity we place targets to cover the boundary domain in a uniform way. For the disk we simply choose an equidistant placement (see e.g. Fig. 8B). In 3d it is accomplished by constructing a geodesic grid, that is by distributing initially a subset of the targets as the vertices of an icosahedron tangent with the sphere, adding the additional ones so that they are equidistant between the vertices of the icosahedron and then projecting all the 3d target locations onto the sphere.

Bottom Line: By funneling protein effectors through needle complexes located on the cellular membrane, bacteria are able to infect host cells during type III secretion events.As a result, theoretical predictions of secretion times are still lacking.Here we provide a model that quantifies, depending on the transport characteristics within bacterial cytoplasm, the amount of time for a protein effector to reach either of the available needle complexes.

View Article: PubMed Central - PubMed

Affiliation: Department of Engineering Mathematics, University of Bristol, Bristol, United Kingdom.

ABSTRACT
By funneling protein effectors through needle complexes located on the cellular membrane, bacteria are able to infect host cells during type III secretion events. The spatio-temporal mechanisms through which these events occur are however not fully understood, due in part to the inherent challenges in tracking single molecules moving within an intracellular medium. As a result, theoretical predictions of secretion times are still lacking. Here we provide a model that quantifies, depending on the transport characteristics within bacterial cytoplasm, the amount of time for a protein effector to reach either of the available needle complexes. Using parameters from Shigella flexneri we are able to test the role that translocators might have to activate the needle complexes and offer semi-quantitative explanations of recent experimental observations.

Show MeSH
Related in: MedlinePlus