Scorpion toxins targeting voltage-gated sodium (Na V ) channels are peptides that comprise 60-76 amino acid residues cross-linked by four disulfide bridges. These toxins can be divided in two groups (a and b toxins), according to their binding properties and mode of action. The scorpion a-toxin Ts2, previously described as a b-toxin, was purified from the venom of Tityus serrulatus, the most dangerous Brazilian scorpion. In this study, seven mammalian Na V channel isoforms (rNa V 1.2, rNa V 1.3, rNa V 1.4, hNa V 1.5, mNa V 1.6, rNa V 1.7 and rNa V 1.8) and one insect Na V channel isoform (DmNa V 1) were used to investigate the subtype specificity and selectivity of Ts2. The electrophysiology assays showed that Ts2 inhibits rapid inactivation of Na V 1.2, Na V 1.3, Na V 1.5, Na V 1.6 and Na V 1.7, but does not affect Na V 1.4, Na V 1.8 or DmNa V 1. Interestingly, Ts2 significantly shifts the voltage dependence of activation of Na V 1.3 channels. The 3D structure of this toxin was modeled based on the high sequence identity (72%) shared with Ts1, another T. serrulatus toxin. The overall fold of the Ts2 model consists of three b-strands and one a-helix, and is arranged in a triangular shape forming a cysteine-stabilized a-helix ⁄ b-sheet (CSab) motif. DatabaseModel data are available in the PMDB under accession number PM0077533.

Homeobox transcription factor A9 (HoxA9) is overexpressed in 70% of patients diagnosed with acute myeloid leukemia (AML), whereas only a small subset of AML patients respond to current differentiation therapies. A cell line overexpressing HoxA9 was derived from the bone marrow of a lysozyme-GFP mouse. In this fashion, GFP served as an endogenous reporter of differentiation, permitting a high-throughput phenotypic screen against the MLPCN library. Two chemical scaffolds were optimized for activity yielding compound ML390, and genetic resistance and sequencing efforts identified dihydroorotate dehydrogenase (DHODH) as the target enzyme. The DHODH inhibitor brequinar works against these leukemic cells as well. The X-ray crystal structure of ML390 bound to DHODH elucidates ML390s binding interactions.

Fumarate hydratases (FHs, fumarases) catalyze the reversible conversion of fumarate into l‐malate. FHs are distributed over all organisms and play important roles in energy production, DNA repair and as tumor suppressors. They are very important targets both in the study of human metabolic disorders and as potential therapeutic targets in neglected tropical diseases and tuberculosis. In this study, human FH (HsFH) was characterized by using enzyme kinetics, differential scanning fluorimetry and X‐ray crystallography. For the first time, the contribution of both substrates was analyzed simultaneously in a single kinetics assay allowing to quantify the contribution of the reversible reaction for kinetics. The protein was crystallized in the spacegroup C2221, with unit‐cell parameters a = 125.43, b = 148.01, c = 129.76. The structure was solved by molecular replacement and refined at 1.8 Å resolution. In our study, a HEPES molecule was found to interact with HsFH at the C‐terminal domain (Domain 3), previously described as involved in allosteric regulation, through a set of interactions that includes Lys 467. HsFH catalytic efficiency is higher when in the presence of HEPES. Mutations at residue 467 have already been implicated in genetic disorders caused by FH deficiency, suggesting that the HEPES‐binding site may be important for enzyme kinetics. This study contributes to the understanding of the HsFH structure and how it correlates with mutation, enzymatic deficiency and pathology.

Galectins are proteins involved in diverse cellular contexts due to their capacity to decipher and respond to the information encoded by β-galactoside sugars. In particular, human galectin-4, normally expressed in the healthy gastrointestinal tract, displays differential expression in cancerous tissues and is considered a potential drug target for liver and lung cancer. Galectin-4 is a tandem-repeat galectin characterized by two carbohydrate recognition domains connected by a linker-peptide. Despite their relevance to cell function and pathogenesis, structural characterization of full-length tandem-repeat galectins has remained elusive. Here, we investigate galectin-4 using X-ray crystallography, small- and wide-angle X-ray scattering, molecular modelling, molecular dynamics simulations, and differential scanning fluorimetry assays and describe for the first time a structural model for human galectin-4. Our results provide insight into the structural role of the linker-peptide and shed light on the dynamic characteristics of the mechanism of carbohydrate recognition among tandem-repeat galectins.