Nuclear-magnetic-resonance study of aggregations and conformations of melanostatin and related peptides.

The 1H and 13C nuclear magnetic resonance spectra of melanostatin (Pro-Leu-Gly-NH2) and related peptides (Pro-Leu-Gly, Z-Pro-Leu-Gly, Z-Pro-Leu-Gly-NH2 and Z-Pro-Leu-Gly-OCH3, where Z = benzyloxycarbonyl) were analysed in a variety of solvents. At physiological pH, the melanostatin molecule is N-protonated in aqueous solution. The concentration dependences of the chemical shifts of amide-proton and carbonyl-carbon resonances and of proton spin-lattice relaxation times were observed in relation to molecular aggregations. In dimethylsulfoxide solution, aggregations were observed for N-protonated melanostatin and Pro-Leu-Gly prepared with HCl and for the Na salt of Z-Pro-Leu-Gly but not for N-protonated melanostatin prepared with HClO4 or HNO3, unprotonated melanostatin, Z-Pro-Leu-Gly-NH2, or Z-Pro-Leu-Gly-OCH3. The leucine NH and glycine CO groups of N-protonated melanostatin are involved in the intermolecular hydrogen bonds of aggregates. The leucine NH group of N-protonated Pro-Leu-Gly also forms the intermolecular hydrogen bond. The solvent and temperature dependences of the chemical shifts of amide-proton and carbonyl-carbon resonances were measured to determine intramolecular hydrogen bonding. In dimethylsulfoxide solution, N-protonated melanostatin molecules in part take the beta-turn structure and the trans carboxamide NH proton and carbonyl oxygen of the proline residue form an intramolecular hydrogen bond.     

Transferred nuclear Overhauser effect analyses of membrane-bound enkephalin analogues by 1H nuclear magnetic resonance: correlation between activities and membrane-bound conformations

Leu-enkephalin, [D-Ala2]Leu-enkephalin, and [D-Ala2]Leu-enkephalinamide (agonists) and [L-Ala2]Leu-enkephalin (inactive analogue) bind to lipid bilayer consisting of phosphatidylcholine and phosphatidylserine. The conformations that these compounds assume, once bound to perdeuterated phospholipid bilayer, have been shown to be unique, as shown by the transferred nuclear Overhauser effect (TRNOE) of 1H NMR spectroscopy. In addition, their location in the bilayer was analyzed by TRNOE in the presence of spin-labeled phospholipids. These analyses showed a clear relationship between the activity and the peptide-membrane interaction. The three active peptides, when bound to membranes, adopt the same conformation, characterized by a type II' beta-turn around Gly3-Phe4 and a gamma-turn around Gly2 (or D-Ala2). The inactive analogue, [L-Ala2]Leu-enkephalin, displayed a completely different TRNOE pattern corresponding to a different conformation in the membrane-bound state. The tyrosine residue of the active compounds is not inserted into the interior of membrane, but it is inserted into the bilayer for the L-Ala2 analogue. According to these results, [L-Ala2]Leu-enkephalin may be explained to be inactive because the mode of binding to the membranes is different from that of active compounds.     

Enzyme domain affects the movement of the voltage sensor in ascidian and zebrafish voltage-sensing phosphatases

The ascidian voltage-sensing phosphatase (Ci-VSP) consists of the voltage sensor domain (VSD) and a cytoplasmic phosphatase region that has significant homology to the phosphatase and tensin homolog deleted on chromosome TEN (PTEN).The phosphatase activity of Ci-VSP is modified by the conformational change of the VSD. In many proteins, two protein modules are bidirectionally coupled, but it is unknown whether the phosphatase domain could affect the movement of the VSD in VSP. We addressed this issue by whole-cell patch recording of gating currents from a teleost VSP (Dr-VSP) cloned from Danio rerio expressed in tsA201 cells. Replacement of a critical cysteine residue, in the phosphatase active center of Dr-VSP, by serine sharpened both ON- and OFF-gating currents. Similar changes were produced by treatment with phosphatase inhibitors, pervanadate and orthovanadate, that constitutively bind to cysteine in the active catalytic center of phosphatases. The distinct kinetics of gating currents dependent on enzyme activity were not because of altered phosphatidylinositol 4,5-bisphosphate levels, because the kinetics of gating current did not change by depletion of phosphatidylinositol 4,5-bisphosphate, as reported by coexpressed KCNQ2/3 channels. These results indicate that the movement of the VSD is influenced by the enzymatic state of the cytoplasmic domain, providing an important clue for understanding mechanisms of coupling between the VSD and its effector.     

Inhibitory activities against topoisomerase I and II by isoaurostatin derivatives and their structure-activity relationships

Isoaurostatin A (IAS-A) isolated from Thermomonospora alba showed weak inhibition against topoisomerase (topo) I (IC(50)=307microM). To get more strong inhibition, derivatives of IAS-A were prepared and their structure-activity relationships against topo I and II were investigated. The addition of hydroxyl group on aromatic rings increased the activities, 3-(3,4,5-trihydroxybenzylidene)-5-hydroxy-3H-benzofuran-2-one (IAS-9) showed strong inhibition (IC(50)=3microM) against topo I. And also, the increasing of hydroxyl group increased growth inhibition against a variety of cancer cells, and IAS-9 showed most potent inhibition. Unlike camptothecin and etoposide, IAS-9 neither stabilized DNA-topo cleavable complex nor intercalated into DNA, and it inhibited topo I and II noncompetitively. The inhibitory activities also increased by opening of lactone ring in the molecule of IAS-9.     

Migration of zebrafish spinal motor nerves into the periphery requires multiple myotome-derived cues

In vertebrate embryos, spinal motor neurons project through segmentally reiterated nerves into the somites. Here, we report that zebrafish secondary motor neurons, which are similar to motor neurons in birds and mammals, depend on myotomal cues to navigate into the periphery. We show that the absence of myotomal adaxial cells in you-too/gli2 embryos severely impairs secondary motor axonal pathfinding, including their ability to project into the somites. Moreover, in diwanka mutant embryos, in which adaxial cells are present but fail to produce cues essential for primary motor growth cones to pioneer into the somites, secondary motor axons display similar pathfinding defects. The similarities between the axonal defects in you-too/gli2 and diwanka mutant embryos strongly suggest that pathfinding of secondary motor axons depends on myotome-derived cues, and that the diwanka gene is a likely candidate to produce or encode such a cue. Our experiments also demonstrate that diwanka plays a central role in the migration of primary and secondary motor neurons, suggesting that both neural populations share mechanisms underlying axonal pathfinding. In summary, we provide compelling evidence that myotomal cells produce multiple signals to initiate and control the migration of spinal nerve axons into the somites.     

Optical and genetic approaches toward understanding neuronal circuits in zebrafish

Optical and genetic tools are beginning to revolutionize thestudies of neuronal circuits. Neurons can now be labeled withconventional or genetically encoded indicators that allow theiractivity to be monitored during behavior in intact animals.Laser ablations and genetic inactivation offer ways to perturbactivity of specific cells to test their contributions to behavior.These approaches promise to speed progress in the understandingof vertebrate networks in genetic model systems such as miceand zebrafish. Here we review some of the progress in applyingthese tools, with an emphasis on our work to develop and applythese approaches in the zebrafish model.     

The influence of bound GDP on the kinetics of guanine nucleotide binding to G proteins

Purified guanine nucleotide-binding regulatory proteins, as either the oligomers or the isolated nucleotide-binding alpha subunits, display anomalous kinetics of nucleotide binding. This is due to the presence of tightly bound GDP in these preparations. The dissociation of bound GDP is the rate-limiting step for nucleotide binding. GDP can be removed by chromatography in the presence of 1 M (NH4)2SO4 and 20% glycerol, which yields preparations of G proteins that contain less than 0.1 mol of GDP/mol of guanosine 5'-(gamma-thio)triphosphate (GTP gamma S)-binding site. When the GDP is removed, the binding of GTP gamma S displays kinetics consistent with a bimolecular reaction.     

Physicochemical properties of the mouse plasmacytoma cell membranes with modified phospholipids

Earlier work from our laboratory has demonstrated that the modification of membrane phospholipid composition markedly retards secretion of immunoglobulin G1 by mouse plasmacytoma MOPC-31C cells. In the present study, we examined the physicochemical properties of lipid vesicles prepared from these cells with modified phospholipids by analyzing temperature dependence of 1H NMR signal line-widths of fatty-acyl chains. The results suggest that the export of IgG1 is affected by the local microenvironment of membranes rather than the bulk fluidity.