Recently, I have heard more and more people talking about protein mobility, what it means and how to measure it. So, I have decided to use this week’s blog as an opportunity to share some of Malvern’s expertise in this area.
Protein mobility, or protein electrophoretic mobility, is essentially the motion of protein molecules under the influence of an electric field that is applied across the fluid that they are dispersed in. The mobility of a protein is directly related to its charge as well as other factors such as electric field strength and ionic strength of the dispersant. Measuring protein mobility makes it possible to calculate protein charge, which relates to a number of other factors such as activity and reaction kinetics, and is of great interest to biochemists.
Sounds easy? In essence it is (with the right instrumentation!) however applying an electric field has been known to cause damage to protein samples by stimulating aggregation. The main consequence of this is that the measured mobility is then more closely related to the mobility of the protein aggregates rather than the protein itself.
Work by scientists at Malvern Instruments has shown that much of the aggregation that occurs during electrophoretic measurements actually takes place at the electrodes [Corbett, Connah & Mattison, Electrophoresis. In press 2011]. The use of the diffusion barrier method, a technique invented and patented by Malvern Instruments, protects the protein sample by isolating it from the cell electrodes [Corbett, Connah & Mattison, Patent Pending]. This means that the applied voltage can be applied for a longer period to generate more reliable data from the measurement. Another useful source of information is the recently published ASTM standard, entitled the “Standard Guide for Measurement of Electrophoretic Mobility and Zeta Potential of Nanosized Biological Materials” (E2865–12), that describes how the diffusion barrier method can be used to measure the mobility and zeta potential in systems containing biological material such as proteins, DNA, liposomes and other similar organic materials.
Zetasizer software includes a dedicated protein mobility measurement protocol, which protects the sample from aggregation by reducing the voltage and carefully controlling the cell temperature to ensure that aggregation does not take place. It also performs a size measurement using exactly the same optics before and after the zeta potential measurement to identify whether any aggregation has occurred during the measurement.
For more information about the diffusion barrier method or protein mobility measurement on a Zetasizer Nano instrument please visit the Malvern Instruments website. Also, keep an eye out for more information about the new addition to the Zetasizer Nano range that will be launching very soon, and attend our webinar on 12th September to be part of our most sensitive launch ever!
To register for the webinar click here