Anja Rosengarth

Oleylethanolamide regulates feeding and body weight through activation of the nuclear receptor PPAR-α

Oleylethanolamide (OEA) is a naturally occurring lipid that regulates satiety and body weight. Although structurally related to the endogenous cannabinoid anandamide, OEA does not bind to cannabinoid receptors and its molecular targets have not been defined. Here we show that OEA binds with high affinity to the peroxisome-proliferator-activated receptor-α (PPAR-α), a nuclear receptor that regulates several aspects of lipid metabolism. Administration of OEA produces satiety and reduces body weight gain in wild-type mice, but not in mice deficient in PPAR-α. Two distinct PPAR-α agonists have similar effects that are also contingent on PPAR-α expression, whereas potent and selective agonists for PPAR-γ and PPAR-β/δ are ineffective. In the small intestine of wild-type but not PPAR-α-null mice, OEA regulates the expression of several PPAR-α target genes: it initiates the transcription of proteins involved in lipid metabolism and represses inducible nitric oxide synthase, an enzyme that may contribute to feeding stimulation. Our results, which show that OEA induces satiety by activating PPAR-α, identify an unexpected role for this nuclear receptor in regulating behaviour, and raise possibilities for the treatment of eating disorders.

A calcium-driven conformational switch of the N-terminal and core domains of annexin A1.

In 1993, Huber and co-workers published the structure of an N-terminally truncated version of human annexin A1 lacking the first 32 amino acid residues (PDB code: 1AIN). In 2001, we reported the structure of full-length porcine annexin A1 including the N-terminal domain in the absence of calcium ions (PDB code: 1HM6). The latter structure did not reflect a typical annexin core fold, but rather a surprising interaction of the N-terminal domain and the core domain. Comparing these two structures revealed that in the full-length structure the first 12 residues of the N-terminal domain insert into the core of the protein, thereby replacing and unwinding one of the alpha-helices (helix D in repeat 3) that is involved in calcium binding. We hypothesized that this structure in the absence of calcium ions represents the inactive form of the protein. Furthermore, we proposed that upon calcium binding, the N-terminal domain would be expelled from the core domain and that the core D-helix would reform in the proper conformation for calcium coordination. Herein, we report the X-ray structure of full-length porcine annexin A1 in the presence of calcium. This new structure shows a typical annexin core structure as we hypothesized, with the D-helix back in place for calcium coordination while parts of the now exposed N-terminal domain are disordered. We could locate eight calcium ions in this structure, two of which are octa-coordinated and two of which were not observed in the structure of the N-terminally truncated annexin A1. Possible implications of this calcium-induced conformational switch for the membrane aggregation properties of annexin A1 will be discussed.

Structure of the human p53 core domain in the absence of DNA.

The tumor suppressor protein p53 plays a key role in cell-cycle regulation by triggering DNA repair, cell-cycle arrest and apoptosis when the appropriate signal is received. p53 has the classic architecture of a transcription factor, with an amino-terminal transactivation domain, a core DNA-binding domain and carboxy-terminal tetramerization and regulatory domains. The crystal structure of the p53 core domain, which includes the amino acids from residue 96 to residue 289, has been determined in the absence of DNA to a resolution of 2.05 A. Crystals grew in a new monoclinic space group (P2(1)), with unit-cell parameters a = 68.91, b = 69.36, c = 84.18 A, beta = 90.11 degrees . The structure was solved by molecular replacement and has been refined to a final R factor of 20.9% (R(free) = 24.6%). The final model contains four molecules in the asymmetric unit with four zinc ions and 389 water molecules. The non-crystallographic tetramers display different protein contacts from those in other p53 crystals, giving rise to the question of how p53 arranges as a tetramer when it binds its target DNA.

Ca2+-independent interaction of annexin I with phospholipid monolayers.

At pH 6.0, the interaction of annexin I, a proteolytic fragment of annexin I and annexin V, was studied with monolayers composed of dipalmitoylphosphatidylserine (DPPS), dipalmitoylphosphatidylcholine (DPPC) or DPPS/DPPC mixtures (molar ratio 1:4). The measurements reveal that only annexin I shows a significant increase in the surface pressure at constant surface area in the absence of Ca2+ ions. We interpret these pressure changes as reflecting penetration of the protein. Kinetic analyses of the annexin I/monolayer interaction at pH 6.0 in the presence and absence of Ca2+ ions show differences between the interaction mechanisms that support the occurrence of a pH‐regulated process. At pH 7.4, Ca2+ ions are required for the interaction.

Cloning, purification and crystallization of full-length human annexin 2

Annexin 2, a Ca(2+)/phospholipid-binding protein, is involved in many biological processes, including membrane aggregation and the modulation of fibrinolytic activity. Here, the expression and purification of recombinant full-length human annexin 2 is reported, as well as crystals obtained by sitting-drop and hanging-drop vapor diffusion at 277 K. A condition consisting of 18% PEG 8000, 0.1 M sodium cacodylate pH 6.5, 0.2 M calcium acetate yielded long needles that diffracted to 3.20 A. Another condition, consisting of 2.5 M NaCl, 0.1 M acetate pH 4.5, 0.2 M Li(2)SO(4), gave crystals with unit-cell parameters a = 48.36, b = 62.86, c = 119.11 A that diffracted to 1.52 A. Both crystals belong to the orthorhombic P2(1)2(1)2(1) space group. The high-resolution 1.52 A data set was collected at ALS beamline 5.0.2 and is 93.0% complete, with an R(sym) of 4.5%. The structure of full-length annexin 2 will provide insight into how its N-terminal domain contributes to its functional role in a variety of biological processes.

Crystallization and preliminary X-ray analysis of full-length annexin I comprising the core and N-­terminal domain

Annexin I, a member of the annexin family of Ca(2+)- and phospholipid-binding proteins, has been crystallized with the complete N-terminus. Annexins are structurally divided into a conserved protein core and an N-terminal domain that is variable in sequence and length. Three-dimensional structures of annexins comprising the protein core and a short N-terminal domain (annexins III, IV, V, VI, XII) or a truncated form almost completely lacking the N-terminal domain (annexins I and II) have been published so far. Here, the crystallization of annexin I comprising not only the core but also the complete N-terminal domain is reported. The crystals belong to the space group P2(1)2(1)2(1), with unit-cell parameters a = 63.6, b = 96.3, c = 127.4 A, and diffract to better than 2 A. Assuming a molecular weight of 38.7 kDa for annexin I and an average value of 2.5 A(3) Da(-1) for V(M), two molecules per asymmetric unit are present.