Seeding Protein Crystallization with Cross-Linked Protein Crystals

Protein crystallization is of great importance because protein crystals have a number of different important applications, including large-scale purification of proteins, determination of protein structure, nanoparticle preparation, and theoretical studies of crystallization. An approach often used to efficiently crystallize proteins is the use of nucleants or seeds (small fragments of protein crystals) that can help increase the probability of protein crystallization. Due to the very positive effect that seeding has on protein crystallization, seeds are now widely accepted and utilized in practical protein crystallization. Here, we show that cross-linked protein crystals (CLPCs), which retain the crystal structure but are much more stable than non-cross-linked crystals, can also be used as a new type of seed for promoting protein crystallization. Seeding with CLPCs has effects on both the reproducibility and screening of protein crystals and could improve the optical perfection (well-defined facets) of protein crystals and the probability of obtaining protein crystals. In addition, the cross-linked protein crystals may reduce the concentration of protein molecules needed to obtain protein crystals. Furthermore, CLPCs are very stable in air, and no protective medium is necessary for the long-term storage of CLPCs. This feature makes the CLPC seeding method a potentially powerful technique in practical protein crystallization on either a laboratorial or an industrial scale.