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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

The MFPT function  of a Brownian particle in a sphere with small spherical targets on its boundary(not shown in the various plots). A visualization of the symmetric arrangements of the targets on the surface of the sphere has been sketched in the Materials and Methods section. The MPFT values are plotted in colour code for each subfigure as function of the particle's starting position  within the sphere. Starting positions are chosen in a smaller spherical region with radius  for clarity. The top row contains values of  of the ‘fast’ model in which   = 0.5 m, m/s and  = 150 Å with , 42 and 92 targets corresponding, respectively, to panel A, B and C. The bottom row shows the results for the ‘slow’ model in which   = 1.1 m, m/s and  = 15 Å with , 20 and 50, corresponding, respectively, to panel D, E and F.
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pone-0041421-g003: The MFPT function of a Brownian particle in a sphere with small spherical targets on its boundary(not shown in the various plots). A visualization of the symmetric arrangements of the targets on the surface of the sphere has been sketched in the Materials and Methods section. The MPFT values are plotted in colour code for each subfigure as function of the particle's starting position within the sphere. Starting positions are chosen in a smaller spherical region with radius for clarity. The top row contains values of of the ‘fast’ model in which  = 0.5 m, m/s and  = 150 Å with , 42 and 92 targets corresponding, respectively, to panel A, B and C. The bottom row shows the results for the ‘slow’ model in which  = 1.1 m, m/s and  = 15 Å with , 20 and 50, corresponding, respectively, to panel D, E and F.

Mentions: Similar parameter dependencies of the MFPT are observed in the 3d domain, with the needle complex bases of S. flexneri now modelled as spherical in shape (Fig. 1B). Similar to the 2d domain, we consider a ‘fast’ and a ‘slow’ model, the former with  = 0.5 m,  = 7.7 m/s,  = 150 Å and the latter with  = 1.1 m,  = 2.5 m/s and  = 15 Å (see Materials and Methods for details). To represent the values of with , we display scatter-cloud plots in Fig. 3, for , 42 or 92 targets. Each point of the cloud corresponds to an initial position of the random walker, and the colour legend reveals the corresonding value of .


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

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

The MFPT function  of a Brownian particle in a sphere with small spherical targets on its boundary(not shown in the various plots). A visualization of the symmetric arrangements of the targets on the surface of the sphere has been sketched in the Materials and Methods section. The MPFT values are plotted in colour code for each subfigure as function of the particle's starting position  within the sphere. Starting positions are chosen in a smaller spherical region with radius  for clarity. The top row contains values of  of the ‘fast’ model in which   = 0.5 m, m/s and  = 150 Å with , 42 and 92 targets corresponding, respectively, to panel A, B and C. The bottom row shows the results for the ‘slow’ model in which   = 1.1 m, m/s and  = 15 Å with , 20 and 50, corresponding, respectively, to panel D, E and F.
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Related In: Results  -  Collection

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

pone-0041421-g003: The MFPT function of a Brownian particle in a sphere with small spherical targets on its boundary(not shown in the various plots). A visualization of the symmetric arrangements of the targets on the surface of the sphere has been sketched in the Materials and Methods section. The MPFT values are plotted in colour code for each subfigure as function of the particle's starting position within the sphere. Starting positions are chosen in a smaller spherical region with radius for clarity. The top row contains values of of the ‘fast’ model in which  = 0.5 m, m/s and  = 150 Å with , 42 and 92 targets corresponding, respectively, to panel A, B and C. The bottom row shows the results for the ‘slow’ model in which  = 1.1 m, m/s and  = 15 Å with , 20 and 50, corresponding, respectively, to panel D, E and F.
Mentions: Similar parameter dependencies of the MFPT are observed in the 3d domain, with the needle complex bases of S. flexneri now modelled as spherical in shape (Fig. 1B). Similar to the 2d domain, we consider a ‘fast’ and a ‘slow’ model, the former with  = 0.5 m,  = 7.7 m/s,  = 150 Å and the latter with  = 1.1 m,  = 2.5 m/s and  = 15 Å (see Materials and Methods for details). To represent the values of with , we display scatter-cloud plots in Fig. 3, for , 42 or 92 targets. Each point of the cloud corresponds to an initial position of the random walker, and the colour legend reveals the corresonding value of .

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