High-resolution structure of proteinase K cocrystallized with digalacturonic acid.

Steven B Larson, John S Day, Chieugiang Nguyen, Robert Cudney, Alexander McPherson

Index: Acta Crystallogr. Sect. F Struct. Biol. Cryst. Commun. 65 , 192-198, (2009)

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Abstract

Proteinase K, a subtilisin-like fungal protease, was crystallized from a cocktail of small molecules containing digalacturonic acid (DGA). The crystal structure was determined to 1.32 A resolution and refined to an R factor of 0.158. The final model contained, beside the protein, two calcium ions, 379 water molecules, a molecule of DGA and a partially occupied HEPES molecule. The DGA molecule has one sugar moiety disposed exactly on a crystallographic twofold axis; the second ring was not observed. The DGA molecule is bound to two protein molecules across the twofold axis through hydrogen-bonding networks involving Ser150 and water molecules. One of the calcium-ion sites has not been reported previously. This study further illustrates the involvement of small molecules in the crystallization of macromolecules through their ability to form intermolecular lattice interactions.