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July 2020 issue
Cover illustration: Structure of flavin-dependent halogenase Xcc4156 [Widmann et al. (2020), Acta Cryst. D76, 687-697]. Chemical halogenation is useful in a range of applications but it requires harsh conditions and may lead to the formation of byproducts owing to a lack of selectivity. Flavin-dependent halogenases have come into focus as a clean alternative because they halogenate their substrates under much milder conditions using halide salts and molecular oxygen. Xcc4156, one of the three brominating Xcc halogenases, has been studied in complex with its cofactor and bromide.
editorial
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Three new Acta Cryst. D Co-editors are introduced.
CCP-EM
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Two approaches for the selection of filaments from cryo-EM micrographs are described.
ISDSB2019
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The innate immune receptor TLR8 can be positively or negatively regulated by small chemical ligands. Structural views of agonist-bound and antagonist-bound forms have revealed the mechanisms underlying agonism and antagonism.
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The current capabilities of and future upgrade plans for the beamlines supporting structural biology at the Canadian Light Source are described.
research papers
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Fast and deterministic methods, based on multi-dimensional scaling and weighted ΔCC1/2, to reject non-isomorphous data sets in multi-data-set crystallography are described, and their successful application to several difficult projects where phasing is based on weak anomalous signal is reported.
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When crystallized in complex with the fluorescent dye 8-anilinonaphthalene-1-sulfonate (ANS) in the presence of melatonin, Hyp-1, a pathogenesis-related class 10 protein from Hypericum perforatum, produced tetartohedrally twinned C2 crystals with commensurate structure modulation, which was interpreted as a ninefold expansion of the unit cell in the c direction. The asymmetric unit of this supercell contains 36 protein molecules (differently populated by 156 ANS ligands) arranged into columns by a combination of ninefold translational noncrystallographic symmetry and pseudotetragonal rotational NCS.
PDB reference: Hyp-1–ANS complex with ninefold structure modulation, 6sjj
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Co-crystal structures of GLIC, a bacterial ligand-gated ion channel, in complex with monocarboxylate and dicarboxylate derivatives are reported. It is shown that binding occurs at two pharmacological sites in the extracellular domain, which is in agreement with the reported effect of some carboxylates as allosteric modulators of GLIC.
The high-resolution X-ray structure of the novel β-type carbonic anhydrase PtLCIB3 from Phaeodactylum tricornutum reveals distinct features in its proton-transfer mechanism.
PDB reference: PtLCIB3, 6kfs
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Xcc4156 is a flavin-dependent halogenase from Xanthomonas campestris. Here, an apo structure is presented which, in combination with soaking experiments, provides functional insight into the binding of FAD and bromide to the halogenase.
PDB reference: Xcc4156, 6y1w
essays
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An essay on Rosalind Franklin marking the 100th anniversary of her birth.
