Evaluation of 5-(2-(4-pyridinyl)vinyl)-6-chloro-3-(1-methyl-2-(S)-pyrrolidinylmethoxy)pyridine and its analogues as PET radioligands for imaging nicotinic acetylcholine receptors

A novel series of compounds derived from the high-affinity nicotinic acetylcholine receptor (nAChR) ligand, 5-(2-(4-pyridinyl)vinyl)-6-chloro-3-((1-methyl-2-(S)-pyrrolidinyl)methoxy)pyridine (Me-p-PVC), originally developed by Abbott Laboratories, was characterized in vitro in nAChR binding assays at 37 degrees C to show K(i) values in the range of 9-611 pm. Several compounds of this series were radiolabeled with (11)C and evaluated in vivo in mice and monkeys as potential candidates for PET imaging of nAChRs. [(11)C]Me-p-PVC (K(i) =56 pm at 37 degrees C; logD = 1.6) was identified as a radioligand suitable for the in vivo imaging of the alpha 4 beta 2* nAChR subtype. Compared with 2-[(18)F]FA, a PET radioligand that has been successfully used in humans and is characterized by a slow kinetic of brain distribution, [(11)C]Me-p-PVC is more lipophilic. As a result, [(11)C]Me-p-PVC accumulated in the brain more rapidly than 2-[(18)F]FA. Pharmacological evaluation of Me-p-PVC in mice demonstrated that the toxicity of this compound was comparable with or lower than that of 2-FA. Taken together, these results suggest that [(11)C]Me-p-PVC is a promising PET radioligand for studying nAChR occupancy by endogenous and exogenous ligands in the brain in vivo.     

Multivalent mechanism of membrane insertion by the FYVE domain

Targeting of a wide variety of proteins to membranes involves specific recognition of phospholipid head groups and insertion into lipid bilayers. For example, proteins that contain FYVE domains are recruited to endosomes through interaction with phosphatidylinositol 3-phosphate (PtdIns(3)P). However, the structural mechanism of membrane docking and insertion by this domain remains unclear. Here, the depth and angle of micelle insertion and the lipid binding properties of the FYVE domain of early endosome antigen 1 are estimated by NMR spectroscopy. Spin label probes incorporated into micelles identify a hydrophobic protuberance that inserts into the micelle core and is surrounded by interfacially active polar residues. A novel proxyl PtdIns(3)P derivative is developed to map the position of the phosphoinositide acyl chains, which are found to align with the membrane insertion element. Dual engagement of the FYVE domain with PtdIns(3)P and dodecylphosphocholine micelles yields a 6-fold enhancement of affinity. The additional interaction of phosphatidylserine with a conserved basic site of the protein further amplifies the micelle binding affinity and dramatically alters the angle of insertion. Thus, the FYVE domain is targeted to endosomes through the synergistic action of stereospecific PtdIns(3)P head group ligation, hydrophobic insertion and electrostatic interactions with acidic phospholipids.     

Identification of unusual fatty acids of four alpine plant species from the Pamirs

Fatty acid composition and structure in total lipids from the green above-ground parts of four alpine plants, Oxygraphis glacialis, Primula macrophylla, Rhodiola pamiroalaica, and Swertia marginata, were established by GC and GC-MS. A total of 55 fatty acids was detected, and 48 of them were identified. Ubiquitous palmitate, linoleate, and linolenate predominated in the lipids accounting for about 72-90% of the total fatty acids. At the same time, the latter contained numerous species, which were unusual for higher plants and included saturated odd-numbered n-acids (six C15-C25 species, 0.26-1.40%), saturated even-numbered very-long-chain n-acids (six C20-C30 species, 1.00-2.49%), iso-acids (nine C15-C26 species, 0.64-1.53%), anteiso-acids (four C15-C20 species, 0.08-1.57%), certain uncommon mono- and dienoic acids, as well as 16:3omega3, 18:3omega6, and 18:4omega3 acids that are absent from the most higher plants. Nine fatty acids were found here for the first time in higher plants and two may be new to science. The evidence on the unusual fatty acids is discussed with respect to their distribution in living organisms, pathways of biosynthesis, and chemotaxonomic role.     

Protein tyrosine phosphatases in the human genome

Tyrosine phosphorylation is catalyzed by protein tyrosine kinases, which are represented by 90 genes in the human genome. Here, we present the set of 107 genes in the human genome that encode members of the four protein tyrosine phosphatase (PTP) families. The four families of PTPases, their substrates, structure, function, regulation, and the role of these enzymes in human disease will be discussed.     

The chromosomal passenger complex is required for chromatin-induced microtubule stabilization and spindle assembly

In cells lacking centrosomes, such as those found in female meiosis, chromosomes must nucleate and stabilize microtubules in order to form a bipolar spindle. Here we report the identification of Dasra A and Dasra B, two new components of the vertebrate chromosomal passenger complex containing Incenp, Survivin, and the kinase Aurora B, and demonstrate that this complex is required for chromatin-induced microtubule stabilization and spindle formation. The failure of microtubule stabilization caused by depletion of the chromosomal passenger complex was rescued by codepletion of the microtubule-depolymerizing kinesin MCAK, whose activity is negatively regulated by Aurora B. By contrast, we present evidence that the Ran-GTP pathway of chromatin-induced microtubule nucleation does not require the chromosomal passenger complex, indicating that the mechanisms of microtubule assembly by these two pathways are distinct. We propose that the chromosomal passenger complex regulates local MCAK activity to permit spindle formation via stabilization of chromatin-associated microtubules.     

Mutational patterns correlate with genome organization in SARS and other coronaviruses

Focused efforts by several international laboratories have resulted in the sequencing of the genome of the causative agent of severe acute respiratory syndrome (SARS), novel coronavirus SARS-CoV, in record time. Using cumulative skew diagrams, I found tht mutational patterns in the SARS-CoV genome were strikingly different from other coronaviruses in terms of mutation rates, although they were in general agreement with the model of the coronavirus lifecycle. These findings might be relevant for the development of sequence-based diagnostics and the design of agents to treat SARS.     

Xrcc4 physically links DNA end processing by polynucleotide kinase to DNA ligation by DNA ligase IV

Nonhomologous end joining (NHEJ) is the major DNA double-strand break (DSB) repair pathway in mammalian cells. A critical step in this process is DNA ligation, involving the Xrcc4-DNA ligase IV complex. DNA end processing is often a prerequisite for ligation, but the coordination of these events is poorly understood. We show that polynucleotide kinase (PNK), with its ability to process ionizing radiation-induced 5'-OH and 3'-phosphate DNA termini, functions in NHEJ via an FHA-dependent interaction with CK2-phosphorylated Xrcc4. Analysis of the PNK FHA-Xrcc4 interaction revealed that the PNK FHA domain binds phosphopeptides with a unique selectivity among FHA domains. Disruption of the Xrcc4-PNK interaction in vivo is associated with increased radiosensitivity and slower repair kinetics of DSBs, in conjunction with a diminished efficiency of DNA end joining in vitro. Therefore, these results suggest a new role for Xrcc4 in the coordination of DNA end processing with DNA ligation.     

On the evolution of erythrocyte programmed cell death: apoptosis of Rana esculenta nucleated red blood cells involves cysteine proteinase activation and mitochondrion permeabilization

Batracian Rana esculenta erythrocytes cell death induced by either calcium influx, or staurosporine, involves typical apoptotic phenotype. Our data reveal: (i) a drastic modification of the cell morphology with loss of the ellipsoidal form as assessed by phase contrast microscopy and scanning electron microscopy; (ii) an exposure of the phosphatidylserine residues in the outer leaflet of the cell membrane; (iii) a caspase-3-like activity; (iv) a mitochondrial membrane potential (Delta Psi m) loss; and (v) a chromatin condensation and fragmentation. Erythrocyte chromatin condensation and fragmentation are prevented by caspase and calpain peptide inhibitors. These inhibitors also prevent Delta Psi m loss supporting the idea that mitochondria is a central sensor for Rana erythrocytes cell death. Our observations highlight the conservation of the programmed cell death machinery in erythrocytes across kingdom.     

PhyloGenie: automated phylome generation and analysis

Phylogenetic reconstruction is the method of choice to determine the homologous relationships between sequences. Difficulties in producing high-quality alignments, which are the basis of good trees, and in automating the analysis of trees have unfortunately limited the use of phylogenetic reconstruction methods to individual genes or gene families. Due to the large number of sequences involved, phylogenetic analyses of proteomes preclude manual steps and therefore require a high degree of automation in sequence selection, alignment, phylogenetic inference and analysis of the resulting set of trees. We present a set of programs that automates the steps from seed sequence to phylogeny and a utility to extract all phylogenies that match specific topological constraints from a database of trees. Two example applications that show the type of questions that can be answered by phylome analysis are provided. The generation and analysis of the Thermoplasma acidophilum phylome with regard to lateral gene transfer between Thermoplasmata and Sulfolobus, showed best BLAST hits to be far less reliable indicators of lateral transfer than the corresponding protein phylogenies.The generation and analysis of the Danio rerio phylome provided more than twice as many proteins as described previously, supporting the hypothesis of an additional round of genome duplication in the actinopterygian lineage.     

Identification of a hydrophobic residue as a key determinant of fructose transport by the facilitative hexose transporter SLC2A7 (GLUT7)

Until recently, the only facilitated hexose transporter GLUT proteins (SLC2A) known to transport fructose were GLUTs 2 and 5. However, the recently cloned GLUT7 can also transport fructose as well as glucose. Comparison of sequence alignments indicated that GLUTs 2, 5, and 7 all had an isoleucine residue at position "314" (GLUT7), whereas the non-fructose-transporting isoforms, GLUTs 1, 3, and 4, had a valine at this position. Mutation of Ile-314 to a valine in GLUT7 resulted in a loss of fructose transport, whereas glucose transport remained completely unaffected. Similar results were obtained with GLUTs 2 and 5. Energy minimization modeling of GLUT7 indicated that Ile-314 projects from transmembrane domain 7 (TM7) into the lumen of the aqueous pore, where it could form a hydrophobic interaction with tryptophan 89 from TM2. A valine residue at 314 appeared to produce a narrowing of the vestibule when compared with the isoleucine. It is proposed that this hydrophobic interaction across the pore forms a selectivity filter restricting the access of some hexoses to the substrate binding site(s) within the aqueous channel. The presence of a selectivity filter in the extracellular vestibule of GLUT proteins would allow for subtle changes in substrate specificity without changing the kinetic parameters of the protein.