Two types of adjacent dimer layers in the low-temperature phase of BaCuSi₂O₆

The low-temperature crystal structure of BaCuSi₂O₆ has been investigated with high-resolution synchrotron x-ray and neutron powder diffraction techniques and has been found to be on average (ignoring the incommensurate modulation) orthorhombic, with the most probable space group Ibam. The Cu-Cu dimers in this material are forming two types of layers with distinctly different interatomic distances. Subtle changes also modify the partially frustrated interlayer Cu-Cu exchange paths. The present results corroborate the interpretation of low-temperature nuclear magnetic resonance and inelastic neutron scattering data in terms of distinct dimer layers. The experimentally determined low-temperature crystal structure of BaCuSi₂O₆ is discussed in terms of its relation to the newer findings of theory and of the complementary experiments.

Molecular mechanism of strigolactone perception by DWARF14

The terpenoid, small-compound strigolactones (SLs) are plant hormones that regulate plant shoot branching, which is an important agronomic trait that determines crop yields. An α/β-hydrolase protein, DWARF14 (D14), has been recognized to be an essential component of plant SL signaling. Recently, it has been demonstrated that D14 interacts with a gibberellin (GA)-signaling repressor SLR1 in an SL-dependent manner [1], which suggests that SLR1 mediates crosstalk between the SL and GA signalings in the regulation of plant shoot branching. Although D14 functions in SL perception to promote the interaction with SLR1, its molecular mechanism remains unclear. Here, we report the crystal structure of D14 in the complex with 5-hydroxy-3-methylbutenolide (D-OH), which is a reaction product of SLs. The structure was solved at a 2.10-Å resolution when an SL synthetic analogue, (–)-ent-2'-epi-GR7, was soaked into D14 crystals [1]. In the complex structure, D-OH was located at a site far from the catalytic residues including H297 and appeared to function as a plug for the catalytic cavity to induce an overall hydrophobic surface with a hydrophilic patch between the two α-helices in the cap structure of D14. In the binding site, the indole amine of Trp205 formed a hydrogen bond with the oxygen atom of the C2' hydroxy group, which arose from the catalytic reaction of D14, instead of a water molecule in the structure of apo D14. In addition, the side chain of Phe245 moved 1.3 Å toward D-OH. Mutational analyses of D14 showed that the interaction between D14 and SLR1 required an enzymatic activity of D14 and the residues Trp205 and Phe245 were essential for the SL-dependent SLR1-binding of D14. These results suggest that the D14–D-OH complex mediates the interaction with SLR1 in which the D-OH-induced surface and/or structural change is crucial.

Educational Outreach and User Training at the Worldwide Protein Data Bank

The Protein Data Bank (PDB) contains a wealth of structural and functional knowledge about proteins, RNA, DNA, and other macromolecules, and their assemblies and complexes with small molecules. The challenge faced by the providers of PDB data is to make this knowledge accessible to an increasingly large and diverse audience, ranging from expert structural biologists to non-specialist consumers of structural information. Educators, students, and general audiences will have their own specific interests and expectations from molecular structure data. For a general user, a 2D image of hemoglobin illustrates how a protein looks at a microscopic level. For high school students and educators, 3D models or computer graphics can show how one or a few specific proteins can assemble into an icosahedral virus. In contrast, PhD and post-doc level researchers require expert guidance on how to critically assess the quality of structural data, and in-depth training on the use of specialist tools and resources for the comparison and analysis of structures. The PDB archive is managed by members of the Worldwide Protein Data Bank (wwPDB): the Research Collaboratory for Structural Bioinformatics Protein Data Bank (RCSB PDB; rcsb.org), Protein Data Bank in Europe (PDBe; pdbe.org), Protein Data Bank Japan (PDBj), and BioMagResBank (BMRB, bmrb.wisc.edu). In addition to managing and distributing structural data, the wwPDB partners are engaged in numerous outreach initiatives and user training programs. These efforts are vital to ensuring that these uniquely valuable data can be effectively accessed and used by research scientists, students, and educators alike. This talk will describe on-going wwPDB outreach efforts and highlight exciting new initiatives at the RCSB PDB, PDBe and PDBj.