title: Structure of a monoclinic polymorph of human carbonic anhydrase II with a doubled a axis.
abstract: The crystal structure of human carbonic anhydrase II with a doubled a axis from that of the usually observed monoclinic unit cell has been determined and refined to 1.4 A resolution. The diffraction data with h = 2n + 1 were systematically weaker than those with h = 2n. Consequently, the scaling of the data, structure solution and refinement were challenging. The two molecules comprising the asymmetric unit are related by a noncrystallographic translation of (1/2) along a, but one of the molecules has two alternate positions related by a rotation of approximately 2 degrees. This rotation axis is located near the edge of the central beta-sheet, causing a maximum distance disparity of 1.7 A between equivalent atoms on the diametrically opposite side of the molecule. The crystal-packing contacts are similar to two sequential combined unit cells along a of the previously determined monoclinic unit cell. Abnormally high final R(cryst) and R(free) values (20.2% and 23.7%, respectively) are not unusual for structures containing pseudo-translational symmetry and probably result from poor signal to noise in the weak h-odd data.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610, USA.
authors.forename: Arthur H
authors.initials: AH
authors.lastname: Robbins
authors.forename: John F
authors.initials: JF
authors.lastname: Domsic
authors.forename: Mavis
authors.initials: M
authors.lastname: Agbandje-McKenna
authors.forename: Robert
authors.initials: R
authors.lastname: McKenna
mesh_terms: D024402:Carbonic Anhydrase II / Q000737:chemistry*; D003460:Crystallization; D018360:Crystallography, X-Ray; D006801:Humans; D008958:Models, Molecular; D011487:Protein Conformation
chemical_list: D024402:Carbonic Anhydrase II
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