title: Crystal structure of the thrombin mutant D221A/D222K: the Asp222:Arg187 ion-pair stabilizes the fast form.
abstract: The thrombin mutant D221A/D222K (ARK) does not bind Na+ and has interesting functional properties intermediate between those of the slow and fast forms of wild type. We solved the X-ray crystal structure of ARK bound at exosite I with a fragment of hirudin at 2.4-A resolution. The structure shows a slight collapse of the 186 and 220 loops into the Na+ binding site due to disruption of the Asp222:Arg187 ion-pair. The backbone O atoms of Arg221a and Lys224 are shifted into conformations that eliminate optimal interaction with Na+. A paucity of solvent molecules in the Na+ binding site is also noted, by analogy to what is seen in the structure of the slow form. These findings reinforce the crucial role of the Asp222:Arg187 ion-pair in stabilizing the fast form of thrombin.
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, Box 8231, St. Louis, MO 63110, USA.
authors.forename: Agustin O
authors.initials: AO
authors.lastname: Pineda
authors.forename: Erli
authors.initials: E
authors.lastname: Zhang
authors.forename: Enriqueta R
authors.initials: ER
authors.lastname: Guinto
authors.forename: Savvas N
authors.initials: SN
authors.lastname: Savvides
authors.forename: Alexander
authors.initials: A
authors.lastname: Tulinsky
authors.forename: Enrico
authors.initials: E
authors.lastname: Di Cera
mesh_terms: D001665:Binding Sites; D003460:Crystallization; D018360:Crystallography, X-Ray; D015951:Factor Xa; D008958:Models, Molecular; D018716:Molecular Mimicry; D020125:Mutation, Missense; D011487:Protein Conformation; D012964:Sodium / Q000737:chemistry; D013917:Thrombin / Q000737:chemistry* / Q000235:genetics
chemical_list: D012964:Sodium; D013917:Thrombin; D015951:Factor Xa