A generic cross-seeding approach to protein crystallization

Obtaining diffraction-quality crystals is often the rate-limiting step during structure determination of biological macromolecules by X-ray crystallography. To address this problem, we investigated a cross-seeding approach with a mixture integrating a heterogeneous set of protein crystal fragments to be used as generic seeds. The fragments are nanometre-sized templates chosen to promote crystal nucleation of protein samples unrelated to the proteins forming the seeds. An atypical crystal form of the human serine hydrolase retinoblastoma binding protein 9 was obtained by adding the mixture to the protein sample before performing standard crystallization assays. The structure was solved by X-ray crystallography at 1.4 Å resolution. Follow-up experiments showed that crystal fragments of α-amylase were critical components in this particular result. The limitations and future applications of our experimental developments are discussed.