Enhanced Stability against Radiation Damage of Lysozyme Crystals Grown in Fmoc-CF Hydrogels

Lysozyme crystals grown in Fmoc-CF (Cys-Phe) hydrogels, unlike those grown in agarose, give rise to composite crystals that have an enhanced resistance against degradation caused by an intense exposure to X-ray irradiation. Fmoc-CF dipeptide shows a clear protection of the most sensitive groups (disulfide bonds and methionines) of the protein. The protection mediated by cysteine is exerted only in its gel state since cysteine in solution has an adverse effect. Probably, the reactive thiol groups of cysteine being locked within the rigid peptide fibers minimize cross-reactions with the proteins favoring the formation of protein crystals. Once located inside the protein crystal, the long peptide fibers are able to protect the protein against radiation damage.