7 research outputs found
Structural basis for a new tetracycline resistance mechanism relying on the TetX monooxygenase.
The flavin-dependent monooxygenase TetX confers resistance to all clinically relevant tetracyclines, including the recently approved, broad-spectrum antibiotic tigecycline (Tygacil®) which is a critical last-ditch defense against multidrug-resistant pathogens. TetX represents the first resistance mechanism against tigecycline, which circumvents both the tet-gene encoded resistances, relying on active efflux of tetracyclines, and ribosomal protection proteins. The alternative enzyme-based mechanism of TetX depends on regioselective hydroxylation of tetracycline antibiotics to 11a-hydroxy-tetracyclines. Here, we report the X-ray crystallographic structure determinations at 2.1Å resolution of native TetX from Bacteroides thetaiotaomicron and its complexes with tetracyclines. Our crystal structures explain the extremely versatile substrate diversity of the enzyme and provide a first step towards the rational design of novel tetracycline derivatives to counter TetX-based resistance prior to emerging clinical observations
Structural Basis for Binding of Fluorescent CMP-Neu5Ac Mimetics to Enzymes of the Human ST8Sia Family
Polysialyltransferases
synthesize polysialic acid on cell surface-expressed
glycoconjugates, which is crucial for developing processes and signaling
pathways in eukaryotes. Recent advances in cancer research have rendered
polysialyltransferases important drug targets because polysialic acid
contributes to cancer cell progression, metastasis, and treatment
of resistant tumors. To aid the development of high-throughput screening
assays for polysialyltransferase inhibitors, we demonstrate that a
previously developed class of fluorescent CMP-sialic acid mimetics
for sialyltransferases has nanomolar affinities for oligo- and polysialyltransferases
and can be used for the rapid screening of new polysialyltransferase
inhibitors. We demonstrate that these CMP-Neu5Ac mimetics inhibit
polysialylation in vitro and perform cell culture experiments, where
we observe reduced polysialylation of NCAM. Furthermore, we describe
the structural basis of CMP-Neu5Ac mimetics binding to the human oligosialyltransferase
ST8SiaIII and extrapolate why their affinity is high for human polysialyltransferases.
Our results show that this novel class of compounds is a promising
tool for the development of potent and selective drugs against polysialyltransferase
activity