Uncertainties in crystallization of hen-egg white lysozyme: reproducibility issue

X-ray transparent microfluidic platforms for membrane protein crystallization with microseeds

Crystallization of membrane proteins is a critical step for uncovering atomic resolution 3-D structures and elucidating structure-function relationships. Microseeding, the process of transferring sub-microscopic crystal nuclei from initial screens into new crystallization experiments, is an effective, yet underutilized approach to grow crystals suitable for X-ray crystallography. Here, we report simplified methods for crystallization of membrane proteins that utilize microseeding in X-ray transparent microfluidic chips. First, a microfluidic method for introduction of microseed dilutions into metastable crystallization experiments is demonstrated for photoactive yellow protein and cytochrome bo3 oxidase. As microseed concentration decreased, the number of crystals decreased while the average size increased. Second, we demonstrate a microfluidic chip for microseed screening, where many crystallization conditions were formulated on-chip prior to mixing with microseeds. Crystallization composition, crystal size, and diffraction data were collected and mapped on phase diagrams, which revealed that crystals of similar diffraction quality and size typically grow in distinct regions of the phase diagram.

Effect of the weather conditions during solution preparation on lysozyme crystallization

Protein crystallization is a delicate process that is always sensitive to environmental factors. When the environmental factors are not well controlled or not controlled at all, identical crystallization droplets from the same mother liquid may yield different crystallization results. One environmental factor, the weather conditions during crystallization solution preparation, is not usually considered as a parameter for protein crystallization. In this paper, it is shown that the weather parameters during preparation of the crystallization experiment, including the ambient temperature, humidity, pressure and particulate matter in the air, can all affect the reproducibility of lysozyme crystallization. An identical lysozyme crystallization experiment was repeated for an entire year, and the weather conditions when each crystallization experiment was set up were recorded along with the crystallization results. Among the parameters recorded, the humidity during the experiment setup showed the strongest effect on lysozyme crystallization. On the basis of these results, it is suggested that the weather conditions during crystallization solution preparation should be considered as a potential factor that can influence protein crystallization.

An ignored variable: solution preparation temperature in protein crystallization

Protein crystallization is affected by many parameters, among which certain parameters have not been well controlled. The temperature at which the protein and precipitant solutions are mixed (i.e., the ambient temperature during mixing) is such a parameter that is typically not well controlled and is often ignored. In this paper, we show that this temperature can influence protein crystallization. The experimental results showed that both higher and lower mixing temperatures can enhance the success of crystallization, which follows a parabolic curve with an increasing ambient temperature. This work illustrates that the crystallization solution preparation temperature is also an important parameter for protein crystallization. Uncontrolled or poorly controlled room temperature may yield poor reproducibility in protein crystallization.

Selecting temperature for protein crystallization screens using the temperature dependence of the second virial coefficient

Protein crystals usually grow at a preferable temperature which is however not known for a new protein. This paper reports a new approach for determination of favorable crystallization temperature, which can be adopted to facilitate the crystallization screening process. By taking advantage of the correlation between the temperature dependence of the second virial coefficient (B(22)) and the solubility of protein, we measured the temperature dependence of B(22) to predict the temperature dependence of the solubility. Using information about solubility versus temperature, a preferred crystallization temperature can be proposed. If B(22) is a positive function of the temperature, a lower crystallization temperature is recommended; if B(22) shows opposite behavior with respect to the temperature, a higher crystallization temperature is preferred. Otherwise, any temperature in the tested range can be used.

Replacing a reservoir solution with desiccant in vapor diffusion protein crystallization screening

This paper presents a modification to the conventional vapor diffusion (hanging- or sitting-drop) technique for protein crystallization screening. In this modified method, the reservoir solution is replaced with a desiccant to allow for a larger range of protein solution concentrations, thereby providing more opportunities for crystal formation. This method was tested in both reproducibility and screening studies, and the results showed that it significantly improves the efficiency and reduces the cost of protein crystallization screens.