Open AccessStructure of a monoclinic polymorph of human carbonic anhydrase II with a doubled a axis
Author(s) -
Robbins Arthur H.,
Domsic John F.,
AgbandjeMcKenna Mavis,
McKenna Robert
Publication year - 2010
Publication title -
acta crystallographica section d
Language(s) - English
Resource type - Journals
ISSN - 1399-0047
DOI - 10.1107/s0907444910006797
Subject(s) - monoclinic crystal system , crystallography , molecule , resolution (logic) , crystal (programming language) , chemistry , crystal structure , rotation (mathematics) , diffraction , translation (biology) , physics , optics , geometry , mathematics , biochemistry , organic chemistry , artificial intelligence , messenger rna , computer science , programming language , gene
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 Å resolution. The diffraction data with h = 2 n + 1 were systematically weaker than those with h = 2 n . 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 ½ along a , but one of the molecules has two alternate positions related by a rotation of approximately 2°. This rotation axis is located near the edge of the central β‐sheet, causing a maximum distance disparity of 1.7 Å 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.