Cross-linked protein crystal technology, as either a protein stabilisation or enzyme immobilisation method, has garnered more attention recently. This method not only can retain the original activity of the protein molecule but can also significantly enhance the crystals' mechanical and chemical stability. This review presents the preparation and mechanism of cross-linked protein crystals using glutaraldehyde. The mechanical, chemical and thermal properties of the cross-linked protein crystals are also reviewed in detail. In addition, this paper summarises the applications of cross-linked protein crystals in the fields of materials science, biosensors, chromatographic analysis, oral delivery and protein crystal quality improvement. Finally, the limitations and perspectives on cross-linked protein crystals are presented.Crystallisation is a well-known approach to obtain highly puri-ed proteins. During crystallisation, protein molecules can be Fig. 2 A schematic diagram of the polymerisation of glutaraldehyde. 21This journal is
Temperature is generally considered as an important factor in protein crystallization. Such is true because crystals usually grow at a preferable temperature in a certain crystallization solution. If a nonsuitable temperature is used, the solution will not yield crystals. However, it is difficult to decide the best temperature suited for screening the crystallization condition of proteins. In this study, it was found out that, compared to constant temperature, a variation in a reasonable range can result in a more efficient crystallization screening. Using the Sparse Matrix Screen with the screening kit Index, this study tested nine commercially available proteins and proved that, compared to the conventional constant temperature strategy, a varying temperature strategy can actually increase the possibility of obtaining crystals. Consequently, the cycling temperature strategy (CTS) is then proposed to be utilized in most screening tasks when the suitable crystallization temperature is unknown.
Containerless processing of materials is considered beneficial for obtaining high quality products due to the elimination of the detrimental effects coming from the contact with container walls. Many containerless processing methods are realized by levitation techniques. This paper describes a containerless levitation setup that utilized the magnetization force generated in a gradient magnetic field. It comprises a levitation unit, a temperature control unit, and a real-time observation unit. Known volume of liquid diamagnetic samples can be levitated in the levitation chamber, the temperature of which is controlled using the temperature control unit. The evolution of the levitated sample is observed in real time using the observation unit. With this setup, containerless processing of liquid such as crystal growth from solution can be realized in a well-controlled manner. Since the levitation is achieved using a superconducting magnet, experiments requiring long duration time such as protein crystallization and simulation of space environment for living system can be easily succeeded.
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