Löf David, Schillén Karin, Jönsson Bengt, Evilevitch Alex
Division of Physical Chemistry 1, Center for Chemistry and Chemical Engineering, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden.
Phys Rev E Stat Nonlin Soft Matter Phys. 2007 Jul;76(1 Pt 1):011914. doi: 10.1103/PhysRevE.76.011914. Epub 2007 Jul 20.
With the aid of time-resolved dynamic light scattering (DLS) and static light scattering (SLS), we have analyzed the ejection kinetics from the bacterial virus bacteriophage (or phage) lambda , triggered in vitro by its receptor. We have used DLS to investigate the kinetics in such a system. Furthermore, we have shown that both SLS and DLS can be interchangeably used to study the process of phage DNA release. DLS is superior to SLS in that it also allows the change in the light scattering arising from each of the components in the system to be monitored under conditions such that the relaxation times are separable. With help of these two methods we present a model explaining the reason for the observed decrease in the scattering intensity accompanying DNA ejection from phage. We emphasize that ejection from phage capsid occurs through a very long tail (which is nearly three times longer than the capsid diameter), which significantly separates ejected DNA from the scattering volume of the capsid. The scattering intensity recorded during the DNA ejection process is the result of a change in the form factor of the phage particle, i.e., the change in the interference effects between the phage capsid and the DNA confined in the phage particle. When the DNA molecule is completely ejected it remains in the proximity of the phage for some time, thus contributing to the scattering signal as it diffuses away from the phage capsid, into the scattering volume and returns to its unperturbed chain conformation in bulk solution. The free DNA chain does not contribute to the scattered intensity, when measured at a large angle, due to the DNA form factor and the low concentration. Although the final diffusion-controlled step can lead to overestimation of the real ejection time, we can still use both scattering methods to estimate the initial DNA ejection rates, which are mainly dependent on the pressure-driven DNA ejection from the phage, allowing studies of the effects of various parameters affecting the ejection.
借助时间分辨动态光散射（DLS）和静态光散射（SLS），我们分析了细菌病毒噬菌体λ在体外由其受体触发后的喷射动力学。我们使用DLS来研究该系统中的动力学。此外，我们已经表明，SLS和DLS都可以交替用于研究噬菌体DNA释放过程。DLS优于SLS之处在于，在弛豫时间可分离的条件下，它还能监测系统中各组分引起的光散射变化。借助这两种方法，我们提出了一个模型，解释了噬菌体DNA喷射时观察到的散射强度降低的原因。我们强调，噬菌体衣壳的喷射是通过一条非常长的尾巴进行的（尾巴长度几乎是衣壳直径的三倍），这使得喷射出的DNA与衣壳的散射体积显著分离。DNA喷射过程中记录的散射强度是噬菌体颗粒形状因子变化的结果，即噬菌体衣壳与限制在噬菌体颗粒内的DNA之间干涉效应的变化。当DNA分子完全喷射出来后，它会在噬菌体附近停留一段时间，因此在从噬菌体衣壳扩散到散射体积并在本体溶液中恢复到未受干扰的链构象时，会对散射信号产生贡献。由于DNA形状因子和低浓度，在大角度测量时，游离DNA链对散射强度没有贡献。尽管最终的扩散控制步骤可能会导致对实际喷射时间的高估，但我们仍然可以使用这两种散射方法来估计初始DNA喷射速率，初始喷射速率主要取决于压力驱动的噬菌体DNA喷射，从而能够研究影响喷射的各种参数的作用。
