No abstract

We discovered a new CK2 inhibitor and revealed its mechanism of action, connecting the circadian clock and cancer regulation.

The crystal structure of adenosine deaminase (ADA) from bovine intestine complexed with a transition-state analogue, 6-hydroxy-1,6-dihydropurine riboside (HDPR), was solved at 2.5 A resolution by the molecular-replacement method using a homology model based on the crystal structure of mouse ADA. The final refinement converged to a crystallographic R factor of 20.7%. The C(alpha) backbone of bovine ADA is mostly superimposable on that of mouse ADA, although mouse ADA itself did not lead to a solution by molecular replacement. HDPR tightly interacts with ADA by means of six hydrogen bonds and is entirely enclosed within the active site. The lid of the envelope consists of two components: one contains two leucine residues, Leu55 and Leu59, and the other contains the backbone atoms Asp182 and Glu183. The C(delta) atoms of the two leucine residues are 3.5 A from the respective N atoms of the backbone. A weak interaction, similar to CH-pi binding, might make it possible to open the lid. Taking account of the movement and observation of this structural feature, the aim is to design novel ADA inhibitors.

No abstract

To help resolve long-standing questions regarding the catalytic activity of the serine proteases, the structure of porcine pancreatic elastase has been analyzed by high-resolution neutron and X-ray crystallography. To mimic the tetrahedral transition intermediate, a peptidic inhibitor was used. A single large crystal was used to collect room-temperature neutron data to 1.65 A resolution and X-ray data to 1.20 A resolution. Another crystal provided a low-temperature X-ray data set to 0.94 A resolution. The neutron data are to higher resolution than previously reported for a serine protease and the X-ray data are comparable with other studies. The neutron and X-ray data show that the hydrogen bond between His57 and Asp102 (chymotrypsin numbering) is 2.60 A in length and that the hydrogen-bonding hydrogen is 0.80-0.96 A from the histidine nitrogen. This is not consistent with a low-barrier hydrogen which is predicted to have the hydrogen midway between the donor and acceptor atom. The observed interaction between His57 and Asp102 is essentially a short but conventional hydrogen bond, sometimes described as a short ionic hydrogen bond. The neutron analysis also shows that the oxygen of the oxopropyl group of the inhibitor is present as an oxygen anion rather than a hydroxyl group, supporting the role of the "oxyanion hole" in stabilizing the tetrahedral intermediate in catalysis.