Investigation of the mechanism of photochemically-induced lysozyme crystallization

•Dimer that have the same alignment as the two adjacent molecules in a crystal exhibit as templates.•Dimers that can become templates are formed between Tyr residues.•The template is formed by the combination of Tyr53–Tyr53 residues.

This work examined the mechanism involved in photoinduced crystallization of a lysozyme, focusing on the structure of the photoproducts that lead to crystal growth. It was determined that dimers formed via linking of tryptophan (Trp) residues are preferentially produced when applying a high-excitation photon fluence. However, these dimers do not lead to crystal growth. A low fluence forms dimers via the combination of tyrosine (Tyr) residues, generating six types of Tyr–Tyr dimers. The dimer that originates from the linking of Tyr53 and Tyr53 has a configuration similar to that of the two adjacent, yet non-linked, lysozyme molecules in the crystal unit cell. The Tyr53–Tyr53 dimer hence acts as a template for lysozyme crystal nucleation.

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