Open AccessType II dehydroquinase: molecular replacement with many copies
Author(s) -
Stewart Kirsty Anne,
Robinson David Alexander,
Lapthorn Adrian Jonathan
Publication year - 2008
Publication title -
acta crystallographica section d
Language(s) - English
Resource type - Journals
ISSN - 1399-0047
DOI - 10.1107/s0907444907054923
Subject(s) - triclinic crystal system , crystallography , molecular replacement , symmetry (geometry) , monomer , crystallographic point group , crystal (programming language) , crystal structure , dodecameric protein , chemistry , symmetry operation , molecular symmetry , molecule , mathematics , geometry , computer science , organic chemistry , programming language , polymer
Type II dehydroquinase is a small (150‐amino‐acid) protein which in solution packs together to form a dodecamer with 23 cubic symmetry. In crystals of this protein the symmetry of the biological unit can be coincident with the crystallographic symmetry, giving rise to cubic crystal forms with a single monomer in the asymmetric unit. In crystals where this is not the case, multiple copies of the monomer are present, giving rise to significant and often confusing noncrystallographic symmetry in low‐symmetry crystal systems. These different crystal forms pose a variety of challenges for solution by molecular replacement. Three examples of structure solutions, including a highly unusual triclinic crystal form with 16 dodecamers (192 monomers) in the unit cell, are described. Four commonly used molecular‐replacement packages are assessed against two of these examples, one of high symmetry and the other of low symmetry; this study highlights how program performance can vary significantly depending on the given problem. In addition, the final refined structure of the 16‐dodecamer triclinic crystal form is analysed and shown not to be a superlattice structure, but rather an F ‐centred cubic crystal with frustrated crystallographic symmetry.