No abstract

Seven human isoforms of importin α mediate nuclear import of cargo in a tissue- and isoform-specific manner. How nuclear import adaptors differentially interact with cargo harbouring the same nuclear localisation signal (NLS) remains poorly understood, as the NLS recognition region is highly conserved. Here, we provide a structural basis for the nuclear import specificity of W proteins in Hendra and Nipah viruses. We determine the structural interfaces of these cargo bound to importin α1 and α3, identifying a 2.4-fold more extensive interface and > 50-fold higher binding affinity for importin α3. Through the design of importin α1 and α3 chimeric and mutant proteins, together with structures of cargo-free importin α1 and α3 isoforms, we establish that the molecular basis of specificity resides in the differential positioning of the armadillo repeats 7 and 8. Overall, our study provides mechanistic insights into a range of important nucleocytoplasmic transport processes reliant on isoform adaptor specificity.

There is a desperate need to develop new antibiotic agents to combat the rise of drug-resistant bacteria, such as clinically important Staphylococcus aureus. The essential multifunctional enzyme, biotin protein ligase (BPL), is one potential drug target for new antibiotics. We report the synthesis and characterization of a series of biotin analogues with activity against BPLs from S. aureus, Escherichia coli, and Homo sapiens. Two potent inhibitors with K i < 100 nM were identified with antibacterial activity against a panel of clinical isolates of S. aureus (MIC 2-16 μg/mL). Compounds with high ligand efficiency and >20-fold selectivity between the isozymes were identified and characterized. The antibacterial mode of action was shown to be via inhibition of BPL. The bimolecular interactions between the BPL and the inhibitors were defined by surface plasmon resonance studies and X-ray crystallography. These findings pave the way for second-generation inhibitors and antibiotics with greater potency and selectivity.

Dysregulation of the inflammatory response underlies numerous diseases. Although most interleukin-1 family cytokines are proinflammatory, human interleukin-37 (IL-37) is a powerful, broad-spectrum inhibitor of inflammation and immunity. We determined the crystal structure of IL-37 to establish the anti-inflammatory mechanism of this key cytokine in view of developing IL-37-based therapies. We found that two β-trefoil fold IL-37 molecules form a head-to-head dimer that is stable in solution. IL-37 variants mutated to convert the cytokine into an obligate monomer were up to 13-fold more effective than the dimer in suppressing proinflammatory events both in primary human blood cells and in vivo in murine endotoxic shock. Therapeutic exploitation of the powerful anti-inflammatory properties of monomeric IL-37 may prove beneficial in treating a wide range of inflammatory and autoimmune disorders.

Summary Protein biotinylation is catalysed by biotin protein ligase (BPL). The most characterized BPL is fromEscherichia coli where it functions as both a biotin ligase and a homodimeric transcriptional repressor. Here we investigated another bifunctional BPL from the clinically important Staphylococcus aureus (SaBPL). Unliganded SaBPL (apo) exists in a dimermonomer equilibrium at low micromolar concentrations -a stark contrast to E. coli BPL (EcBPL) that is monomeric under the same conditions. EMSA and SAXS analysis demonstrated that dimeric apo SaBPL adopted a conformation that was competent to bind DNA and necessary for it to function as a transcription factor. The SaBPL dimer-monomer dissociation constant was 5.8-fold tighter when binding the inhibitor biotin acetylene, but unchanged with biotin. F123, located in the dimer interface, was critical for homodimerization. Inhibition studies together with surface plasmon resonance analyses revealed a strong correlation between inhibitor potency and slow dissociation kinetics. A 24-fold difference in K i values for these two enzymes was explained by differences in enzyme:inhibitor dissociation rates. Substitution of F123 in SaBPL and its equivalent in EcBPL altered both inhibitor potency and dissociation. Hence, F123 in SaBPL has novel roles in both protein dimerization and ligand-binding that have not been reported in EcBPL.

A 'leaky mutant' (SaBPL-R122G) of Staphylococcus aureus biotin protein ligase (SaBPL) is used to enhance the turnover rate for the reaction of biotin alkyne with an azide to give a triazole. This allows the enzyme to select the optimum triazole-based inhibitor using a library of such azides in a single experiment with greatly improved efficiency and sensitivity of detection, difficulties that can restrict the general utility of a multi-component in situ click approach to ligand optimisation.

No abstract

The global increase in multi-drug-resistant bacteria is severely impacting our ability to effectively treat common infections. For Gram-negative bacteria, their intrinsic and acquired resistance mechanisms are heightened by their unique cell wall structure. The cell wall, while being a target of some antibiotics, represents a barrier due to the inability of most antibacterial compounds to traverse and reach their intended target. This means that its composition and resulting mechanisms of resistance must be considered when developing new therapies. Here, we discuss potential antibiotic targets within the most well-characterised resistance mechanisms associated with the cell wall in Gram-negative bacteria, including the outer membrane structure, porins and efflux pumps. We also provide a timely update on the current progress of inhibitor development in these areas. Such compounds could represent new avenues for drug discovery as well as adjuvant therapy to help us overcome antibiotic resistance.