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Emergent chemical behavior in variable-volume protocells.

Shirt-Ediss B, Solé RV, Ruiz-Mirazo K - Life (Basel) (2015)

Bottom Line: One prominent feature of vesicles is the semi-permeable nature of their membranes, able to support passive diffusion of individual solute species into/out of the compartment, in addition to an osmotic water flow in the opposite direction to the net solute concentration gradient.Focusing on bistability, we demonstrate how a changing volume compartment can degenerate existing bistable reactions, but also promote emergent bistability from very simple reactions, which are not bistable in bulk conditions.Our results suggest that other chemical innovations should be expected when more realistic and active properties of protocellular compartments are taken into account.

View Article: PubMed Central - PubMed

Affiliation: ICREA-Complex Systems Lab, Institut de Biologia Evolutiva, CSIC-UPF, 08003 Barcelona, Spain. ben@shirt-ediss.me.

ABSTRACT
Artificial protocellular compartments and lipid vesicles have been used as model systems to understand the origins and requirements for early cells, as well as to design encapsulated reactors for biotechnology. One prominent feature of vesicles is the semi-permeable nature of their membranes, able to support passive diffusion of individual solute species into/out of the compartment, in addition to an osmotic water flow in the opposite direction to the net solute concentration gradient. Crucially, this water flow affects the internal aqueous volume of the vesicle in response to osmotic imbalances, in particular those created by ongoing reactions within the system. In this theoretical study, we pay attention to this often overlooked aspect and show, via the use of a simple semi-spatial vesicle reactor model, that a changing solvent volume introduces interesting non-linearities into an encapsulated chemistry. Focusing on bistability, we demonstrate how a changing volume compartment can degenerate existing bistable reactions, but also promote emergent bistability from very simple reactions, which are not bistable in bulk conditions. One particularly remarkable effect is that two or more chemically-independent reactions, with mutually exclusive reaction kinetics, are able to couple their dynamics through the variation of solvent volume inside the vesicle. Our results suggest that other chemical innovations should be expected when more realistic and active properties of protocellular compartments are taken into account.

No MeSH data available.


Related in: MedlinePlus

Switching dynamics: bistability in two unimolecular reactions. Encapsulating two unimolecular reactions X→Y and P→Q in the variable-volume vesicle reactor model gives a bistable system under the correct parameter regime (Figure 2c(i)). Below, switching dynamics between steady states SS1 and SS2 are demonstrated by injecting molecules into the reactor by a simulated syringe. Following four different two-minute injections of molecules, changes in (a) spherical vesicle diameter, (b) vesicle internal species numbers and (c) vesicle internal species concentrations are monitored. Injection I1 releases both X and Q into the vesicle at a linear rate of 1000 molecules per second. This perturbation is not sufficiently strong to switch the reactor into SS2, but injection I2, releasing X and Q at 3500 molecules per second, is able to prompt the transition. Once in the larger vesicle SS2 state, the switch back to SS1 is achieved by injecting a new species U into the reactor. This species undergoes reaction , which depletes Q inside the vesicle by quickly transforming it into waste W (k = 60.0) that rapidly diffuses out of the compartment (). Injection I3 releases U into the vesicle at a rate of 8000 molecules per second, but cannot initiate the switch back to SS1. Injection I4 successfully completes the transition, releasing U at a rate of 10, 000 molecules per second. Time is divided into windows to accommodate different timescales (from minutes to days).
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life-05-00181-f004: Switching dynamics: bistability in two unimolecular reactions. Encapsulating two unimolecular reactions X→Y and P→Q in the variable-volume vesicle reactor model gives a bistable system under the correct parameter regime (Figure 2c(i)). Below, switching dynamics between steady states SS1 and SS2 are demonstrated by injecting molecules into the reactor by a simulated syringe. Following four different two-minute injections of molecules, changes in (a) spherical vesicle diameter, (b) vesicle internal species numbers and (c) vesicle internal species concentrations are monitored. Injection I1 releases both X and Q into the vesicle at a linear rate of 1000 molecules per second. This perturbation is not sufficiently strong to switch the reactor into SS2, but injection I2, releasing X and Q at 3500 molecules per second, is able to prompt the transition. Once in the larger vesicle SS2 state, the switch back to SS1 is achieved by injecting a new species U into the reactor. This species undergoes reaction , which depletes Q inside the vesicle by quickly transforming it into waste W (k = 60.0) that rapidly diffuses out of the compartment (). Injection I3 releases U into the vesicle at a rate of 8000 molecules per second, but cannot initiate the switch back to SS1. Injection I4 successfully completes the transition, releasing U at a rate of 10, 000 molecules per second. Time is divided into windows to accommodate different timescales (from minutes to days).

Mentions: Figure 2c(i) demonstrates that vesicle bistability can emerge quite unexpectedly in our vesicle reactor model from two chemically-independent unimolecular reactions:(15)X→k1YP→c1Qwhen these reactions share the internal volume of the vesicle. Figure 4 further explores this interesting case, showing the time dynamics of switching between SS1 and SS2, prompted by extra molecules being injected into the vesicle reactor by a simulated syringe.


Emergent chemical behavior in variable-volume protocells.

Shirt-Ediss B, Solé RV, Ruiz-Mirazo K - Life (Basel) (2015)

Switching dynamics: bistability in two unimolecular reactions. Encapsulating two unimolecular reactions X→Y and P→Q in the variable-volume vesicle reactor model gives a bistable system under the correct parameter regime (Figure 2c(i)). Below, switching dynamics between steady states SS1 and SS2 are demonstrated by injecting molecules into the reactor by a simulated syringe. Following four different two-minute injections of molecules, changes in (a) spherical vesicle diameter, (b) vesicle internal species numbers and (c) vesicle internal species concentrations are monitored. Injection I1 releases both X and Q into the vesicle at a linear rate of 1000 molecules per second. This perturbation is not sufficiently strong to switch the reactor into SS2, but injection I2, releasing X and Q at 3500 molecules per second, is able to prompt the transition. Once in the larger vesicle SS2 state, the switch back to SS1 is achieved by injecting a new species U into the reactor. This species undergoes reaction , which depletes Q inside the vesicle by quickly transforming it into waste W (k = 60.0) that rapidly diffuses out of the compartment (). Injection I3 releases U into the vesicle at a rate of 8000 molecules per second, but cannot initiate the switch back to SS1. Injection I4 successfully completes the transition, releasing U at a rate of 10, 000 molecules per second. Time is divided into windows to accommodate different timescales (from minutes to days).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4390847&req=5

life-05-00181-f004: Switching dynamics: bistability in two unimolecular reactions. Encapsulating two unimolecular reactions X→Y and P→Q in the variable-volume vesicle reactor model gives a bistable system under the correct parameter regime (Figure 2c(i)). Below, switching dynamics between steady states SS1 and SS2 are demonstrated by injecting molecules into the reactor by a simulated syringe. Following four different two-minute injections of molecules, changes in (a) spherical vesicle diameter, (b) vesicle internal species numbers and (c) vesicle internal species concentrations are monitored. Injection I1 releases both X and Q into the vesicle at a linear rate of 1000 molecules per second. This perturbation is not sufficiently strong to switch the reactor into SS2, but injection I2, releasing X and Q at 3500 molecules per second, is able to prompt the transition. Once in the larger vesicle SS2 state, the switch back to SS1 is achieved by injecting a new species U into the reactor. This species undergoes reaction , which depletes Q inside the vesicle by quickly transforming it into waste W (k = 60.0) that rapidly diffuses out of the compartment (). Injection I3 releases U into the vesicle at a rate of 8000 molecules per second, but cannot initiate the switch back to SS1. Injection I4 successfully completes the transition, releasing U at a rate of 10, 000 molecules per second. Time is divided into windows to accommodate different timescales (from minutes to days).
Mentions: Figure 2c(i) demonstrates that vesicle bistability can emerge quite unexpectedly in our vesicle reactor model from two chemically-independent unimolecular reactions:(15)X→k1YP→c1Qwhen these reactions share the internal volume of the vesicle. Figure 4 further explores this interesting case, showing the time dynamics of switching between SS1 and SS2, prompted by extra molecules being injected into the vesicle reactor by a simulated syringe.

Bottom Line: One prominent feature of vesicles is the semi-permeable nature of their membranes, able to support passive diffusion of individual solute species into/out of the compartment, in addition to an osmotic water flow in the opposite direction to the net solute concentration gradient.Focusing on bistability, we demonstrate how a changing volume compartment can degenerate existing bistable reactions, but also promote emergent bistability from very simple reactions, which are not bistable in bulk conditions.Our results suggest that other chemical innovations should be expected when more realistic and active properties of protocellular compartments are taken into account.

View Article: PubMed Central - PubMed

Affiliation: ICREA-Complex Systems Lab, Institut de Biologia Evolutiva, CSIC-UPF, 08003 Barcelona, Spain. ben@shirt-ediss.me.

ABSTRACT
Artificial protocellular compartments and lipid vesicles have been used as model systems to understand the origins and requirements for early cells, as well as to design encapsulated reactors for biotechnology. One prominent feature of vesicles is the semi-permeable nature of their membranes, able to support passive diffusion of individual solute species into/out of the compartment, in addition to an osmotic water flow in the opposite direction to the net solute concentration gradient. Crucially, this water flow affects the internal aqueous volume of the vesicle in response to osmotic imbalances, in particular those created by ongoing reactions within the system. In this theoretical study, we pay attention to this often overlooked aspect and show, via the use of a simple semi-spatial vesicle reactor model, that a changing solvent volume introduces interesting non-linearities into an encapsulated chemistry. Focusing on bistability, we demonstrate how a changing volume compartment can degenerate existing bistable reactions, but also promote emergent bistability from very simple reactions, which are not bistable in bulk conditions. One particularly remarkable effect is that two or more chemically-independent reactions, with mutually exclusive reaction kinetics, are able to couple their dynamics through the variation of solvent volume inside the vesicle. Our results suggest that other chemical innovations should be expected when more realistic and active properties of protocellular compartments are taken into account.

No MeSH data available.


Related in: MedlinePlus