The crystal structure of the catalytic core of murine terminal deoxynucleotidyltransferase (TdT) at 2.35 A Ê resolution reveals a typical DNA polymerase b-like fold locked in a closed form. In addition, the structures of two different binary complexes, one with an oligonucleotide primer and the other with an incoming ddATP-Co 2+ complex, show that the substrates and the two divalent ions in the catalytic site are positioned in TdT in a manner similar to that described for the human DNA polymerase b ternary complex, suggesting a common two metal ions mechanism of nucleotidyl transfer in these two proteins. The inability of TdT to accommodate a template strand can be explained by steric hindrance at the catalytic site caused by a long lariat-like loop, which is absent in DNA polymerase b. However, displacement of this discriminating loop would be suf®cient to unmask a number of evolutionarily conserved residues, which could then interact with a template DNA strand. The present structure can be used to model the recently discovered human polymerase m, with which it shares 43% sequence identity.

Synchrotron X-ray data have been collected to 1.4 Å resolution at the NE-CAT beam-line at the Advanced Photon Source from fibers of cellulose I b and regenerated cellulose II (Fortisan) at ambient temperature and at 100 K in order to understand the effects of low temperature on cellulose more thoroughly. Crystal structures have been determined at each temperature. The unit cell of regenerated cellulose II contracted, with decreasing temperature, by 0.25%, 0.22% and 0.1% along the a, b, and c axes, respectively, whereas that of cellulose I b contracted only in the direction of the a axis, by 0.9%. The value of 4.6Â10 )5 K )1 for the thermal expansion coefficient of cellulose I b in the a axis direction can be explained by simple harmonic molecular oscillations and the lack of hydrogen-bonding in this direction. The molecular conformations of each allomorph are essential unchanged by cooling to 100 K. The room temperature crystal structure of regenerated cellulose II is essentially identical to the crystal structure of mercerized cellulose II.

Certain leukocytes release serine proteases that sustain inflammatory processes and cause disease conditions, such as asthma and chronic obstructive pulmonary disease. We identified ␤-ketophosphonate 1 (JNJ-10311795; RWJ-355871) as a novel, potent dual inhibitor of neutrophil cathepsin G (K i ‫؍‬ 38 nM) and mast cell chymase (K i ‫؍‬ 2.3 nM). The x-ray crystal structures of 1 complexed with human cathepsin G (1.85 Å) and human chymase (1.90 Å) reveal the molecular basis of the dual inhibition. Ligand 1 occupies the S 1 and S 2 subsites of cathepsin G and chymase similarly, with the 2-naphthyl in S 1 , the 1-naphthyl in S 2 , and the phosphonate group in a complex network of hydrogen bonds. Surprisingly, however, the carboxamido-N-(naphthalene-2-carboxyl)piperidine group is found to bind in two distinct conformations. In cathepsin G, this group occupies the hydrophobic S 3 /S 4 subsites, whereas in chymase, it does not; rather, it folds onto the 1-naphthyl group of the inhibitor itself. Compound 1 exhibited noteworthy antiinflammatory activity in rats for glycogen-induced peritonitis and lipopolysaccharide-induced airway inflammation. In addition to a marked reduction in neutrophil influx, 1 reversed increases in inflammatory mediators interleukin-1␣, interleukin-1␤, tissue necrosis factor-␣, and monocyte chemotactic protein-1 in the glycogen model and reversed increases in airway nitric oxide levels in the lipopolysaccharide model. These findings demonstrate that it is possible to inhibit both cathepsin G and chymase with a single molecule and suggest an exciting opportunity in the treatment of asthma and chronic obstructive pulmonary disease.

Vitamin K antagonists are widely used anticoagulants targeting vitamin K epoxide reductases (VKOR), a family of integral membrane enzymes. To elucidate their catalytic cycle and inhibitory mechanism, here we report eleven x-ray crystal structures of human VKOR and pufferfish VKOR-like with substrates and antagonists in different redox states. Substrates entering the active site in a partially oxidized state form a cysteine adduct that induces an open-to-closed conformational change, triggering reduction. Binding and catalysis is facilitated by hydrogen-bonding interactions in a hydrophobic pocket. The antagonists bind specifically to the same hydrogen-bonding residues and induce a similar closed conformation. Thus, vitamin K antagonists act through mimicking the key interactions and conformational changes required for the VKOR catalytic cycle.