5-Amino-2,4,6-triiodo­isophthalic acid monohydrate

The title compound, C8H4I3NO4·H2O, shows an extensive hydrogen-bond network; in the crystal structure, mol­ecules are linked by O—H⋯O, N—H⋯O and O—H⋯N hydrogen bonds involving all possible donors and also the water mol­ecule

The magic triangle goes MAD: experimental phasing with a bromine derivative

5-Amino-2,4,6-tribromoisophthalic acid is used as a phasing tool for protein structure determination by MAD phasing. It is the second representative of a novel class of compounds for heavy-atom derivatization that combine heavy atoms with amino and carboxyl groups for binding to proteins

Enhanced rigid-bond restraints

An extension is proposed to the rigid-bond description of atomic thermal motion in crystals

Crystal structure of trioxacarcin A covalently bound to DNA

We report a crystal structure that shows an antibiotic that extracts a nucleobase from a DNA molecule ‘caught in the act’ after forming a covalent bond but before departing with the base. The structure of trioxacarcin A covalently bound to double-stranded d(AACCGGTT) was determined to 1.78 Å resolution by MAD phasing employing brominated oligonucleotides. The DNA–drug complex has a unique structure that combines alkylation (at the N7 position of a guanine), intercalation (on the 3′-side of the alkylated guanine), and base flip-out. An antibiotic-induced flipping-out of a single, nonterminal nucleobase from a DNA duplex was observed for the first time in a crystal structure

ANODE: anomalous and heavy-atom density calculation

The program ANODE determines anomalous (or heavy-atom) densities by reversing the usual procedure for experimental phase determination. Instead of adding a phase shift to the heavy-atom phases to obtain a starting value for the native protein phase, this phase shift is subtracted from the native phase to obtain the heavy-atom substructure phase

Methyl 9H-xanthene-9-carboxyl­ate

The title compound, C15H12O3, was obtained unintentionally as the by-product of an attempted recrystallization from methanol of propantheline bromide, an anti­muscarinic drug. The xanthone unit is folded, with a dihedral angle of 24.81 (9)° between the benzene rings. The ester substituent adopts a trans staggered conformation, with a C—C—O—C torsion angle of 178.4 (1)°. The mol­ecules pack in distinct layers, facilitated by C—H⋯π and weak π–π ring inter­actions. A weak C—H⋯O inter­action also occurs; however, no classical hydrogen bonding is observed

Structure of sulfamidase provides insight into the molecular pathology of mucopolysaccharidosis IIIA

Mucopolysaccharidosis type IIIA (Sanfilippo A syndrome), a fatal childhood-onset neurodegenerative disease with mild facial, visceral and skeletal abnormalities, is caused by an inherited deficiency of the enzyme N-sulfoglucosamine sulfohydrolase (SGSH; sulfamidase). More than 100 mutations in the SGSH gene have been found to reduce or eliminate its enzymatic activity. However, the molecular understanding of the effect of these mutations has been confined by a lack of structural data for this enzyme. Here, the crystal structure of glycosylated SGSH is presented at 2Å resolution. Despite the low sequence identity between this unique N-sulfatase and the group of O-sulfatases, they share a similar overall fold and active-site architecture, including a catalytic formylglycine, a divalent metal-binding site and a sulfate-binding site. However, a highly conserved lysine in O-sulfatases is replaced in SGSH by an arginine (Arg282) that is positioned to bind the N-linked sulfate substrate. The structure also provides insight into the diverse effects of pathogenic mutations on SGSH function in mucopolysaccharidosis type IIIA and convincing evidence for the molecular consequences of many missense mutations. Further, the molecular characterization of SGSH mutations will lay the groundwork for the development of structure-based drug design for this devastating neurodegenerative disorder. © 2014 International Union of Crystallography.This work was funded by the DFG. Partial support from DFG grant No. SH 14/5-1 is gratefully acknowledged (NSS). IU is grateful to the Spanish MEC and Generalitat de Catalunya for financial support (grants BFU2012-35367, IDC-20101173 and 2009SGR-1036)Peer Reviewe

Practical structure solution with ARCIMBOLDO

ARCIMBOLDO combines the location of small fragments with Phaser and density modification with SHELXE of all possible Phaser solutions. Its uses are explained and illustrated through practical test cases

4,10-Diall­yloxy-1,2,3,6b,7,8,9,12b-octa­hydro­perylene

In the title compound, C26H28O2, the central atoms are coplanar, with the –CH2—CH2– links of the cyclo­hexene groups lying to either side of the plane and with the diall­yloxy residues twisted out of this plane [C—C—O—C torsion angles = 16.6 (3) and −13.9 (3)°]. In the crystal structure, mol­ecules are connected into chains propagating in [100] via C—H⋯π inter­actions