The Effect of 2-methyl-2,4-pentanediol on the Crystal Structure of Lysozyme

Abstract

Chiral control of crystallization has ample precedent in the small-molecule world, but relatively little work has been carried out to investigate the role of chirality in protein crystallization. In this study, lysozyme was crystallized in the presence of the chiral additive 2-methyl-2,4-pentanediol (MPD), using the (R) and (S) enantiomers as well as the racemic (RS) mixture. The crystals grown with (R)-MPD had the least disorder and produced the highest resolution protein structures. This result is consistent with the observation that for (R)- and (RS)-MPD, the crystal contacts are made by (R)-MPD demonstrating that there is preferential interaction between lysozyme and this enantiomer. These findings support the hypothesis that chiral interactions are important in protein crystallization. Additionally, to confirm the conformational assignment of MPD in our crystal structures, the conformations of MPD molecules in crystal structures from the Protein Data Bank were examined. Using the number of occurrences of each conformer, the relative energies of the conformers were calculated. It was shown that MPD favors the conformation that allows for an intramolecular hydrogen bond between its hydroxyl groups and maintains an anti-anti configuration for its carbon backbone, which corresponds to the conformer found in our crystals.