Two types of endogenous cannabinoid-receptor agonists have been identified thus far. They are the ethanolamides of polyunsaturated fatty acids-arachidonoyl ethanolamide (anandamide) is the best known compound in the amide series-and 2-arachidonoyl glycerol, the only known endocannabinoid in the ester series. We report now an example of a third, ether-type endocannabinoid, 2-arachidonyl glyceryl ether (noladin ether), isolated from porcine brain. The structure of noladin ether was determined by mass spectrometry and nuclear magnetic resonance spectroscopy and was confirmed by comparison with a synthetic sample. It binds to the CB1 cannabinoid receptor (Ki ‫؍‬ 21.2 ؎ 0.5 nM) and causes sedation, hypothermia, intestinal immobility, and mild antinociception in mice. It binds weakly to the CB2 receptor (Ki > 3 M).W e have reported the isolation and identification of two types of endogenous cannabinoids that bind and activate the known cannabinoid receptors CB 1 and CB 2 . Arachidonoyl ethanolamide (anandamide; ref. 1) and later two more polyunsaturated fatty acid ethanol amides (2) were found in porcine brain. An ester, 2-arachidonoyl glycerol (2-AG) was isolated by us from canine gut (3) and by Sugiura et al. from brain (4). Anandamide and 2-AG have been the objects of numerous investigations in various areas of biology and have been found to affect processes in the nervous, cardiovascular, immune, and reproductive systems (5-8). They interact with many neurotransmitters and affect hormone levels (9-10). This ubiquity of effects led us to look for additional endocannabinoids.We report now that we have isolated from porcine brain a third endocannabinoid, 2-arachidonyl glyceryl ether, which we have named noladin ether ( Fig. 1). Materials and MethodsIsolation of Noladin Ether. Porcine brain (100 g, approximately a single brain) was added to a mixture of chloroform (200 ml) and methanol (200 ml) and mixed in a blender for 2 min. Water (100 ml) was added, and the mixing process was continued for another minute. The mixture was filtered. Two layers were formed. The water-methanol layer was separated and evaporated under reduced pressure. The residue obtained was extracted with methanol. The above isolation was repeated numerous times (from a total of 2.4 kg porcine brain). The extract obtained was chromatographed on a gravity column (i.d. 2.5 cm, height 28 cm, 82 g ICN Silica TSC, 60 A) with hexane͞acetone initially in a ratio of 10:1 (vol͞vol) (400 ml), then 9:1 (100 ml), and finally 4:1 (100 ml). The fractions eluted were monitored for binding to the CB 1 receptor from rat brain synaptosomes (prepared as described below; ref. 11) on the basis of displacement of the potent labeled agonist [ 3 H]HU-243 purchased from Tocris (Bristol, U.K.). The material eluted in fractions 45-54 (10-ml each) was found to bind to the receptor. These fractions were combined and purified further by HPLC (see below). A polar-active compound developed on a TLC plate (silica gel 60 F 254 , Merck) in a hexane͞ acetone (4:1) solvent system gave ...

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Crystal structures have shown that the HIV-1 protease flaps, domains that control access to the active site, are closed when the active site is occupied by a ligand. Although flap structures ranging from closed to semi-open are observed in the free protease, crystal structures reveal that even the semi-open flaps block access to the active site, indicating that the flaps are mobile in solution. The goals of this paper are to characterize the secondary structure and fast (sub-ns) dynamics of the flaps of the free protease in solution, to relate these results to X-ray structures and to compare them with predictions of dynamics calculations. To this end we have obtained nearly complete backbone and many sidechain signal assignments of a fully active free-protease construct that is stabilized against autoproteolysis by three point mutations. The secondary structure of this protein was characterized using the chemical shift index, measurements of 3h J NCЈ couplings across hydrogen bonds, and NOESY connectivities. Analysis of these measurements indicates that the protease secondary structure becomes irregular near the flap tips, residues 49-53. Model-free analysis of 15 N relaxation parameters, T 1 , T 2 (T 1 ) and 15 N-{ 1 H} NOE, shows that residues in the flap tips are flexible on the sub-ns time scale, in contrast with previous observations on the inhibitor-bound protease. These results are compared with theoretical predictions of flap dynamics and the possible biological significance of the sub-ns time scale dynamics of the flap tips is discussed.

To better understand the structural requirements for selective cytotoxicity of antimicrobial peptides, seven dermaseptin S4 analogs were produced and investigated with respect to molecular organization in solution, binding properties to model phospholipid membranes, and cytotoxic properties. Native dermaseptin S4 displayed high aggregation in solution and high binding affinity. These properties correlated with high cytotoxicity. Yet, potency was progressively limited when facing cells whose plasma membrane was surrounded by increasingly complex barriers. Increasing the positive charge of the native peptide led to partial depolymerization that correlated with higher binding affinity and with virtually non-discriminative high cytotoxicity against all cell types. The C-terminal hydrophobic domain was found responsible for binding to membranes but not for their disruption. Truncations of the C terminus combined with increased positive charge of the Nterminal domain resulted in short peptides having similar binding affinity as the parent compound but displaying selective activity against microbes with reduced toxicity toward human red blood cells. Nuclear magnetic resonance-derived three-dimensional structures of three active derivatives enabled the delineation of a common amphipathic structure with a clear separation of two lobes of positive and negative electrostatic potential surfaces. Whereas the spatial positive electrostatic potential extended considerably beyond the peptide dimensions and was required for potency, selectivity was affected primarily by hydrophobicity. The usefulness of this approach for the design of potent and/or selective cytolytic peptides is discussed herein.