Crystal Structure of the TLR4-MD-2 Complex with Bound Endotoxin Antagonist Eritoran

SummaryTLR4 and MD-2 form a heterodimer that recognizes LPS (lipopolysaccharide) from Gram-negative bacteria. Eritoran is an analog of LPS that antagonizes its activity by binding to the TLR4-MD-2 complex. We determined the structure of the full-length ectodomain of the mouse TLR4 and MD-2 complex. We also produced a series of hybrids of human TLR4 and hagfish VLR and determined their structures with and without bound MD-2 and Eritoran. TLR4 is an atypical member of the LRR family and is composed of N-terminal, central, and C-terminal domains. The β sheet of the central domain shows unusually small radii and large twist angles. MD-2 binds to the concave surface of the N-terminal and central domains. The interaction with Eritoran is mediated by a hydrophobic internal pocket in MD-2. Based on structural analysis and mutagenesis experiments on MD-2 and TLR4, we propose a model of TLR4-MD-2 dimerization induced by LPS

Purification and characterization of Alu I methylase

Alu I methylase has been isolated from 300g (wet weight) cells of Arthrobacter luteus. After ammonium sulfate fractionation, the protein which has methylase activity was purified through phosphocellulose, DEAE-cellulose, Heparin agarose, and Hydroxylapatite column chromatography. The methylated DNA by the purified methylase was resistatnt against Alu I endonuclease. The purified Alu I methylase was essentially homogeneous as judged by 10% SDS-polyacrylamide gel electrophoresis, and the apparent subunit molecular weight was 56,000±1,000. The specific activity of the enzyme was 1.32 × 105 units per mg protein.Accepted versio

The specificity and catalytic properties of Alu I methylase

The specific methylation site for Alu I methylase was the cytosine nucleotide in Alu I sequence. The position of the methylated cytosine nucleotide was determined by the chemical cleavage reactions of the Maxam-Gilbert DNA sequencing procedure. As expected, the methylated cytosine nucleotide bands were disappeared on C+ T and C lanes on 12% sequencing gels. Alu I methylase was maximally active at near pH 7.5 in the presence of 50 mM NaCl. The methylase did not require Mg++ for activity, and obeyed Michaelis-Menten Kinetics with respect to both AdoMet and DNA. At 37°C, the Km for AdoMet was 0.44 μM, that for the Alu I site of pBR 322 DNA was 4.03 nM, and the corresponding turnover numbers were 1.83 methyl transfer per minute per monomer and 1.61 transfers per minute per monomer, respectively.Accepted versio