Toll-like receptor (TLR)-10 remains an orphan receptor without well-characterized ligands or functions. Here, we reveal that TLR10 is predominantly localized to endosomes and binds dsRNA in vitro at endosomal pH, suggesting that dsRNA is a ligand of TLR10. Recognition of dsRNA by TLR10 activates recruitment of myeloid differentiation primary response gene 88 for signal transduction and suppression of interferon regulatory factor-7 dependent type I IFN production. We also demonstrate crosstalk between TLR10 and TLR3, as they compete with each other for dsRNA binding. Our results suggest for the first time that dsRNA is a ligand for TLR10 and propose novel dual functions of TLR10 in regulating IFN signaling: first, recognition of dsRNA as a nucleotide-sensing receptor and second, sequestration of dsRNA from TLR3 to inhibit TLR3 signaling in response to dsRNA stimulation.

Development of potent biocatalysts for enzymatic detoxification of estrogenic mycotoxin zearalenone (ZEN) and its more toxic derivative α-zearalenol (α-ZOL) is of great interest. Here, we report the crystal structures of a ZEN-hydrolyzing enzyme from Rhinocladiella mackenziei (RmZHD), including substrate complexes. A molecular mechanism for the distinct activity of RmZHD in hydrolyzing the structurally similar ZEN and α-ZOL is then proposed. In addition, structure-based engineering to modify the substratebinding pocket and improve the RmZHD activity toward α-ZOL is presented. These results expand our scope in understanding the catalytic mechanism of ZHD-family enzymes and are of vital importance in further industrial applications.

We report the first structure of heptaprenyl diphosphate synthase from Staphylococcus aureus (SaHepPPS), together with an investigation of its mechanism of action, and inhibition. The protein is involved in the formation of menaquinone, a key electron transporter in many bacteria, including pathogens. SaHepPPS consists of a “catalytic” subunit (SaHepPPS-2) having two “DDXXD” motifs and a “regulatory” subunit (SaHepPPS-1) that lacks these motifs. High concentrations of the substrates, isopentenyl diphosphate and farnesyl diphosphate, inhibit the enzyme, which is also potently inhibited by bisphosphonates. The most active inhibitors (Ki ~ 200 nM) were N-alkyl analogs of zoledronate containing ~C6 alkyl side-chains. They were modestly active against S. aureus cell growth, and growth inhibition was partially “rescued” by addition of menaquinone-7. Since SaHepPPS is essential for S. aureus cell growth, its structure is of interest in the context of the development of menaquinone biosynthesis inhibitors as potential antibiotic leads.