The first crystal structure of human cyclooxygenase-2, in the presence of a selective inhibitor, is similar to that of cyclooxygenase-1. The structure of the NSAID binding site is also well conserved, although there are differences in its overall size and shape which may be exploited for the further development of selective COX-2 inhibitors. A second COX-2 structure with a different bound inhibitor displays a new, open conformation at the bottom of the NSAID binding site, without significant changes in other regions of the COX-2 structure. These two COX-2 structures provide evidence for the flexible nature of cyclooxygenase, revealing details about how substrate and inhibitor may gain access to the cyclooxygenase active site from within the membrane.

No abstract

Oxidative modification converts low-density lipoprotein (LDL) into its atherogenic form and appears to be a necessary precondition for LDL uptake by macrophages during foam cell formation. Cellular lipoxygenases have been implicated in this process. We studied the interaction of purified mammalian lipoxygenases with human LDL in v i m and found that the arachidonate 15-lipoxygenases of rabbit and man are capable of oxygenating lipoproteins as indicated by oxygen uptake and by the formation of thiobarbituric-acid-reactive substances. Furthermore, oxygenated polyenoic fatty acids, such as 13-hydro(pero)xy-9Z, 11 E-octadecadienoic acid and 15-hydro(pero)xy-5,8,11,13 (Z,Z, Z,E)-eicosatetraenoic acid were detected in the lipid compartment of various lipoproteins classes after lipoxygenase treatment. More than 90% of the oxygenated polyenoic fatty acids were found in the ester-lipid fraction, particularly in the cholesterol esters, whereas only small amounts of free hydro(pero)xy polyenoic fatty acids were detected. Lipoxygenase-catalyzed oxygenation of LDL is not restricted to the lipid compartment but also leads to a cooxidative modification of the apoproteins as indicated by changes in the electrophoretic mobility and by the formation of carbonyl derivatives of amino acid side chains. The possible biological significance of lipoxygenase-induced oxidative modification of lipoproteins in the pathogenesis of atherosclerosis is discussed.Atherosclerosis is a multifactoral disease, the pathogenesis of which is not fully understood [l-31. It has been shown by morphological studies that the accumulation of lipid-loaded foam cells in the subendothelial space leads to the formation of fatty streaks, which are generally accepted as the early atherosclerotic lesions [l -41. Foam cells develop from monocyte-derived macrophages [5, 61 or from smooth muscle cells [7] by taking up modified low-density lipoproteins (LDL) via scavenger-receptor(s)-mediated pathways. The occurrence of oxidatively modified proteins in atherosclerotic lesions [8, 91 and the fact that oxidatively modified LDL is rapidly taken up by macrophages [lo] suggested an involvement of oxidative processes in the pathogenesis of atherosclerosis. However, the mechanism of oxidative modification in vivo remains unclear. In-vitro studies with cell-free systems indicated that copper-mediated oxidation converts LDL into its atherogenic form [ll] The oxygenation of lipoproteins by mammalian lipoxygenases has not been studied so far. The soybean lipoxygenase which largely differs from mammalian lipoxygenases with respect to its protein chemical and enzymic properties is capable of oxidizing LDL only in the presence of phospholipase A, which provides free polyenoic fatty acids by cleaving lipoprotein phospholipids [20]. This result is not surprising since the soybean lipoxygenase has been shown to effectively oxygenate ester lipids only in the presence of detergents [21]. However, the rabbit reticulocyte lipoxygenase is capable of oxygenating complex ester lipids such ...

No abstract

IL-1R-associated kinase (IRAK)4 plays a central role in innate and adaptive immunity, and is a crucial component in IL-1/TLR signaling. We have determined the crystal structures of the apo and ligand-bound forms of human IRAK4 kinase domain. These structures reveal several features that provide opportunities for the design of selective IRAK4 inhibitors. The N-terminal lobe of the IRAK4 kinase domain is structurally distinctive due to a loop insertion after an extended N-terminal helix. The gatekeeper residue is a tyrosine, a unique feature of the IRAK family. The IRAK4 structures also provide insights into the regulation of its activity. In the apo structure, two conformations coexist, differing in the relative orientation of the two kinase lobes and the position of helix C. In the presence of an ATP analog only one conformation is observed, indicating that this is the active conformation.