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The structure of bovine β‐lactoglobulin in crystals grown at pH 3.8 exhibiting novel threefold twinning
Author(s) -
Yeates Todd O.,
McPherson Alexander
Publication year - 2019
Publication title -
acta crystallographica section f
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.572
H-Index - 37
ISSN - 2053-230X
DOI - 10.1107/s2053230x1901224x
Subject(s) - crystallography , crystal twinning , protein data bank (rcsb pdb) , molecular replacement , chemistry , molecule , crystal structure , group (periodic table) , crystal (programming language) , crystallization , conformational isomerism , stereochemistry , microstructure , organic chemistry , computer science , programming language
Bovine β‐lactoglobulin was crystallized from 3 M NaCl buffered at pH 3.8 with sodium citrate as thick hexagonal prisms of greater than 1 mm in edge length. Analyses of the X‐ray diffraction intensities using three different current algorithms were unanimous in specifying the space group to be P 6 3 22, with unit‐cell dimensions a = b = 75.47, c = 140.79 Å. No progress could be made, however, towards an acceptable solution by molecular replacement using this symmetry. In the end, it was found that the true space group was C 222 1 , a subgroup of P 6 3 22, with a = 65.89, b = 114.12, c = 140.51 Å, with the apparent 622 symmetry arising from an unusual threefold or tritohedral twinning. An assembly based on a model of the protein in another crystal form (PDB entry 1beb) containing three molecules in the asymmetric unit was refined to 2.3 Å resolution with a final R factor of 0.23 and R free of 0.26. NCS restraints were maintained throughout. For the most part, the molecules found in this crystal form are virtually the same as in PDB entry 1beb, although there are numerous local variations, particularly in loop elements, rotamer conformation differences and some alterations, including additions, at the termini.