title: High-resolution structure of proteinase K cocrystallized with digalacturonic acid.
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.
authors.affiliation: Department of Molecular Biology and Biochemistry, The University of California, Irvine, 92697-3900, USA.
authors.forename: Steven B
authors.initials: SB
authors.lastname: Larson
authors.forename: John S
authors.initials: JS
authors.lastname: Day
authors.forename: Chieugiang
authors.initials: C
authors.lastname: Nguyen
authors.forename: Robert
authors.initials: R
authors.lastname: Cudney
authors.forename: Alexander
authors.initials: A
authors.lastname: McPherson
mesh_terms: D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D003460:Crystallization; D018360:Crystallography, X-Ray; D004187:Disaccharides / Q000737:chemistry*; D019286:Endopeptidase K / Q000737:chemistry*; D008958:Models, Molecular; D013400:Sugar Acids / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D004187:Disaccharides; D013400:Sugar Acids; D019286:Endopeptidase K; C090179:digalacturonic acid; D002118:Calcium