| 1. |
- Freeman, Krista G., et al.
(författare)
-
Portal Stability Controls Dynamics of DNA Ejection from Phage
- 2016
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 120:26, s. 6421-6429
-
Tidskriftsartikel (refereegranskat)abstract
- Through a unique combination of time-resolved single-molecule (cryo-TEM) and bulk measurements (light scattering and small-angle X-ray scattering), we provide a detailed study of the dynamics of stochastic DNA ejection events from phage λ. We reveal that both binding with the specific phage receptor, LamB, and thermo-mechanical destabilization of the portal vertex on the capsid are required for initiation of ejection of the pressurized λ-DNA from the phage. Specifically, we found that a measurable activation energy barrier for initiation of DNA ejection with LamB present, Ea = (1.2 ± 0.1) × 10-19 J/phage (corresponding to ∼28 kTbody/phage at Tbody = 37 °C), results in 15 times increased rate of ejection event dynamics when the temperature is raised from 15 to 45 °C (7.5 min versus 30 s average lag time for initiation of ejection). This suggests that phages have a double fail-safe mechanism for ejection - in addition to receptor binding, phage must also overcome (through thermal energy and internal DNA pressure) an energy barrier for DNA ejection. This energy barrier ensures that viral genome ejection into cells occurs with high efficiency only when the temperature conditions are favorable for genome replication. At lower suboptimal temperatures, the infectious phage titer is preserved over much longer times, since DNA ejection dynamics is strongly inhibited even in the presence of solubilized receptor or susceptible cells. This work also establishes a light scattering based approach to investigate the influence of external solution conditions, mimicking those of the bacterial cytoplasm, on the stability of the viral capsid portal, which is directly linked to dynamics of virion deactivation.
|
|
| 2. |
- Ishikawa, Kazuhiro, et al.
(författare)
-
Microemulsions of Record Low Amphiphile Concentrations Are Affected by the Ambient Gravitational Field
- 2016
-
Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 120:26, s. 6074-6079
-
Tidskriftsartikel (refereegranskat)abstract
- It is shown that the ternary system heavy water-heptane-hexadecyl hexaethylene oxide (C16E6) has a stable bicontinuous microemulsion phase down to an exceptionally low concentration at the balanced temperature of 26.8 °C. It is further demonstrated that the ambient gravitational field has an influence on the observed phase equilibria for typical sample sizes (∼1 cm). Direct measurements using a nuclear magnetic resonance imaging technique demonstrate that sample compositions vary with the height in the vials. It is furthermore found that some samples show four phases at equilibrium in apparent violation of Gibbs' phase rule. It is pointed out that Gibbs' phase rule strictly applies only when effects of gravity are negligible. A further consequence of the ambient gravitational field is that, for the system studied, the microemulsion one-phase samples are not observed, when using standard size vials, that is, sample heights on the order of a centimeter. Quantitative determinations of concentration profiles can be used to determine parameters of the free-energy density for the system.
|
|
