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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 disk with symmetrically located targets(as shown e.g. in Fig. 1a). Its values are plotted as a surface which depends on the particle's starting position  in the bottom plane of each figure. The surface colour is added only to clarify points of a large MFPT (red shading) against a small MFPT (blue shading). In the top row  is computed for the ‘fast’ model in which   = 0.5 m, m/s and  = 150 Å, with , 20 and 50, correspondingly, respectively, to panel A, B and C. The bottom row shows the results for the ‘slow’ model in which   = 0.5 m, m/s and  = 15 Å, and with , 20 and 50, correspondingly, respectively, to panel D, E and F.
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pone-0041421-g002: The MFPT function of a Brownian particle in a disk with symmetrically located targets(as shown e.g. in Fig. 1a). Its values are plotted as a surface which depends on the particle's starting position in the bottom plane of each figure. The surface colour is added only to clarify points of a large MFPT (red shading) against a small MFPT (blue shading). In the top row is computed for the ‘fast’ model in which  = 0.5 m, m/s and  = 150 Å, with , 20 and 50, correspondingly, respectively, to panel A, B and C. The bottom row shows the results for the ‘slow’ model in which  = 0.5 m, m/s and  = 15 Å, and with , 20 and 50, correspondingly, respectively, to panel D, E and F.

Mentions: For explanatory purposes, we first focus our attention on the 2d case: a single Brownian walker confined to a disk whose edge possesses a number of equidistant circular targets (illustrated in Fig. 1A). We fix the disk radius to 0.5 m corresponding to the size of a cross-section of S. flexneri perpendicular to its longitudinal axis [15]. The corresponding diffusion coefficient is varied from 2.5 to 7.7 m/s, in agreement with fluorescence studies on protein mobility in E. Coli[17] (see Materials and Methods section). Accordingly, we construct two different scenarios: one ‘fast’ model for which the effector diffuses with diffusion coefficient m/s and the target radius of the needle complexes equals 150 Å, and a ‘slow’ model for which m/s and target radii are 15 Å. The resulting values of the MFPT, , are shown in Fig. 2 as function of the effector's initial position , for , 20 and 50 targets, respectively.


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 disk with symmetrically located targets(as shown e.g. in Fig. 1a). Its values are plotted as a surface which depends on the particle's starting position  in the bottom plane of each figure. The surface colour is added only to clarify points of a large MFPT (red shading) against a small MFPT (blue shading). In the top row  is computed for the ‘fast’ model in which   = 0.5 m, m/s and  = 150 Å, with , 20 and 50, correspondingly, respectively, to panel A, B and C. The bottom row shows the results for the ‘slow’ model in which   = 0.5 m, m/s and  = 15 Å, and with , 20 and 50, correspondingly, respectively, to panel D, E and F.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3412870&req=5

pone-0041421-g002: The MFPT function of a Brownian particle in a disk with symmetrically located targets(as shown e.g. in Fig. 1a). Its values are plotted as a surface which depends on the particle's starting position in the bottom plane of each figure. The surface colour is added only to clarify points of a large MFPT (red shading) against a small MFPT (blue shading). In the top row is computed for the ‘fast’ model in which  = 0.5 m, m/s and  = 150 Å, with , 20 and 50, correspondingly, respectively, to panel A, B and C. The bottom row shows the results for the ‘slow’ model in which  = 0.5 m, m/s and  = 15 Å, and with , 20 and 50, correspondingly, respectively, to panel D, E and F.
Mentions: For explanatory purposes, we first focus our attention on the 2d case: a single Brownian walker confined to a disk whose edge possesses a number of equidistant circular targets (illustrated in Fig. 1A). We fix the disk radius to 0.5 m corresponding to the size of a cross-section of S. flexneri perpendicular to its longitudinal axis [15]. The corresponding diffusion coefficient is varied from 2.5 to 7.7 m/s, in agreement with fluorescence studies on protein mobility in E. Coli[17] (see Materials and Methods section). Accordingly, we construct two different scenarios: one ‘fast’ model for which the effector diffuses with diffusion coefficient m/s and the target radius of the needle complexes equals 150 Å, and a ‘slow’ model for which m/s and target radii are 15 Å. The resulting values of the MFPT, , are shown in Fig. 2 as function of the effector's initial position , for , 20 and 50 targets, respectively.

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