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Biomedical subjects

J B Thompson

Publications and source records attributed to J B Thompson.

At least 19 recordsLinked to original sources
PubMed2002

Segmented nanofibers of spider dragline silk: atomic force microscopy and single-molecule force spectroscopy.

Despite its remarkable materials properties, the structure of spider dragline silk has remained unsolved. Results from two probe microscopy techniques provide new insights into the structure of spider dragline silk. A soluble synthetic protein from dragline silk spontaneously forms nanofibers, as observed by atomic force microscopy. These nanofibers have a segmented substructure. The segment length and amino acid sequence are consistent with a slab-like shape for individual silk protein molecules. The height and width of nanofiber segments suggest a stacking pattern of slab-like molecules in each nanofiber segment. This stacking pattern produces nano-crystals in an amorphous matrix, as observed previously by NMR and x-ray diffraction of spider dragline silk. The possible importance of nanofiber formation to native silk production is discussed. Force spectra for single molecules of the silk protein demonstrate that this protein unfolds through a number of rupture events, indicating a modular substructure within single silk protein molecules. A minimal unfolding module size is estimated to be around 14 nm, which corresponds to the extended length of a single repeated module, 38 amino acids long. The structure of this spider silk protein is distinctly different from the structures of other proteins that have been analyzed by single-molecule force spectroscopy, and the force spectra show correspondingly novel features.

Amino Acid Sequence↗
PubMed2001

Bone indentation recovery time correlates with bond reforming time.

Despite centuries of work, dating back to Galileo, the molecular basis of bone's toughness and strength remains largely a mystery. A great deal is known about bone microsctructure and the microcracks that are precursors to its fracture, but little is known about the basic mechanism for dissipating the energy of an impact to keep the bone from fracturing. Bone is a nanocomposite of hydroxyapatite crystals and an organic matrix. Because rigid crystals such as the hydroxyapatite crystals cannot dissipate much energy, the organic matrix, which is mainly collagen, must be involved. A reduction in the number of collagen cross links has been associated with reduced bone strength and collagen is molecularly elongated ('pulled') when bovine tendon is strained. Using an atomic force microscope, a molecular mechanistic origin for the remarkable toughness of another biocomposite material, abalone nacre, has been found. Here we report that bone, like abalone nacre, contains polymers with 'sacrificial bonds' that both protect the polymer backbone and dissipate energy. The time needed for these sacrificial bonds to reform after pulling correlates with the time needed for bone to recover its toughness as measured by atomic force microscope indentation testing. We suggest that the sacrificial bonds found within or between collagen molecules may be partially responsible for the toughness of bone.

Animals↗
PubMed2001

Stereocontrolled synthesis of cis-dibenzoquinolizine chlorofumarates: curare-like agents of ultrashort duration.

The quaternizations of dibenzoquinolizines 9 and 14 with 3-halo-1-propanols are highly cis-selective (94-100% cis), results consistent with the N-methylation of O-methylcapaurine (7b), but in contrast to the proposed trans-stereochemistry of dibenzo[a,h]quinolizine methiodide 10 and the analogous quaternizations of 1-benzyl- and 1-phenylisoquinoline congeners 5b and 5c. In this report, we describe stereoselective preparation of the unique cis-dibenzoquinolizinium propanols 15 and 16and their transformation into bis- and mixed-onium chlorofumarates 19, 20ab, and 26. Dibenzo[a,g]quinolizinium propanol 15 was prepared enantioselectively in three steps from dihydroisoquinoline 11. Asymmetric transfer hydrogenation of 11 in the presence of triethylamine/formic acid and Noyori's chiral ruthenium catalyst 12 produced R-(-)-5',8-dimethoxynorlaudanosine (13) in 98% yield and 87% ee. Pictet-Spengler cyclization of 13 in formalin/formic acid afforded the dibenzo[a,g]quinolizine 14 in 65% yield. Quaternization of 14 with 3-chloro-1-propanol under Finkelstein conditions generated cis-dibenzoquinolizinium propanol 15 in 85% yield with >94% cis-selectivity. The cis-dibenzo[a,h]quinolizinium propanol 16 was obtained as a single stereoisomer by reaction of the known tetramethoxyquinolizine 9 with neat 3-iodo-1-propanol. Bis-onium chlorofumarates 18 and 19 and the mixed-onium derivative 20ab were prepared by a pool synthesis procedure from (1R)-trans-6a, 16, and chlorofumaryl chloride (17). Mixed-onium alpha-chlorofumarate 26 was synthesized from (1S)-trans-6d, 15 and (+/-)-trans-2,3-dichlorosuccinic anhydride (22), employing a recently disclosed chlorofumarate mixed-diester synthesis. The title compounds (19, 20ab, and 26) displayed curare-like effects of ultrashort duration in rhesus monkeys.

Animals↗
PubMed2000

Direct observation of the transition from calcite to aragonite growth as induced by abalone shell proteins.

The mixture of EDTA-soluble proteins found in abalone nacre are known to cause the nucleation and growth of aragonite on calcite seed crystals in supersaturated solutions of calcium carbonate. Past atomic force microscope studies of the interaction of these proteins with calcite crystals did not observe this transition because no information about the crystal polymorph on the surface was obtained. Here we have used the atomic force microscope to directly observe changes in the atomic lattice on a calcite seed crystal after the introduction of abalone shell proteins. The observed changes are consistent with a transition to (001) aragonite growth on a (1014) calcite surface.

Animal Structures↗
PubMed2000

Probing protein-protein interactions in real time.

We have used a prototype small cantilever atomic force microscope to observe, in real time, the interactions between individual protein molecules. In particular, we have observed individual molecules of the chaperonin protein GroES binding to and then dissociating from individual GroEL proteins, which were immobilized on a mica support. This work suggests that the small cantilever atomic force microscope is a useful tool for studying protein dynamics at the single molecule level.

Aluminum Silicates↗
PubMed1999

Synthesis of ultra-short-acting neuromuscular blocker GW 0430: a remarkably stereo- and regioselective synthesis of mixed tetrahydroisoquinolinium chlorofumarates.

[formula: see text] The stereo- and regioselective synthesis of ultra-short-acting nondepolarizing neuromuscular blocker GW 0430 (5a) is described. Key steps involved the enantioselective transfer hydrogenation of imine 8 employing Noyori's catalyst, the stereoselective crystallization and methanolysis of trans-bataines 11 and 12, and the stereo- and regioselective trans elimination of hydrogen chloride from 14. The latter transformation allowed complete control of the position of the chloro substituent and stereochemistry at the double bond of the linker in 15.

Crystallization↗
PubMed1998

Cotransfection of second and third intracellular loop fragments inhibit angiotensin AT1a receptor activation of phospholipase C in HEK-293 cells.

Peptides from the intracellular regions of G protein-coupled receptors are useful probes of receptor-G protein coupling mechanisms. As a first step toward the genetic delivery of such "G protein inhibitors," we describe inhibition of angiotensin II (AII) receptor responses by expressed fragments of the second and third intracellular loops of the AT1a receptor (AT1a/i2 and AT1a/i3). Transient transfection of human embryonic kidney 293 cells with DNA encoding the rat AT1a receptor resulted in AII-dependent increases of inositol phosphates (maximum 4.5-fold). Cotransfection of AT1a/i2 and AT1a/i3 fragments raised the EC50 for AII stimulation of phospholipase C activity 5-fold (from 0.18 nM to 0.99 nM, n = 12, P < .001) and 3-fold (from 0.38 nM to 1.2 nM, n = 8, P < .002), respectively. The combined effect of AT1a/i2 and AT1a/3 was additive, and transfection of an alpha-1b adrenergic receptor third intracellular loop (alpha1b/i3) fragments also increased the EC50 for AII. Neither AT1a/i1 nor C-terminus (AT1a/Ct) constructs had significant effects on angiotensin responses. These data confirm a role for the second and third intracellular loops in angiotensin receptor responses and show the potential of this approach to blocking multiple phospholipase C-linked receptors.

Animals↗
PubMed1997

Whiting events: biogenic origin due to the photosynthetic activity of cyanobacterial picoplankton.

An annual whiting event occurs each year in late May to early June in Fayetteville Green Lake, New York. The initiation of this event correlates with exponential growth of the Synechococcus population within the lake. Synechococcus is the dominant (by approximately 4 orders of magnitude) autotrophic organism owing to the oligotrophic condition of the lake. The delta 13C values of the dissolved inorganic C range seasonally from -9.5% in winter to -6.2% in summer due to photosynthetic activity. Calcite precipitates principally in the microenvironment surrounding Synechococcus because of a photosynthetically driven alkalization process and the availability of the cells as nucleation sites. This calcite has a heavier delta 13C value (>4%) than does the dissolved inorganic C of the lake water owing to the cells' preferential uptake of 12C. A conceptual model suggests that photosynthetic activity and cell surface chemistry, together with the substantial surface area that arises from the great abundance of micron-sized cells, allow Synechococcus to dominate the annual whiting events in Fayetteville Green Lake.

Calcium Carbonate↗
PubMed1996

Synthesis and evaluation of heterocyclic carboxamides as potential antipsychotic agents.

Heterocyclic analogues of 1192U90, 2-amino-N-(4-(4-(1,2-benzisothiazol-3-yl)-1-piperazinyl)-butyl) benzamide hydrochloride (1), were prepared and evaluated as potential antipsychotic agents. These analogues were evaluated in vitro for their binding to the dopamine D2, serotonin 5-HT2, and serotonin 5-HT1a receptors and in vivo for their ability to antagonize the apomorphine-induced climbing response in mice. Nine different types of heterocyclic carboxamides were studied in this investigation (i.e., pyridine-, thiophene-, benzothiophene-, quinoline-, 1,2,3,4-tetrahydroquinoline-, 2,3-dihydroindole-, indole-, benzimidazole-, and indazolecarboxamides). Two derivatives exhibited potent in vivo activities comparable to 1: 3-amino-N-(4-(4-(1,2-benzisothiazol-3-yl)-1-piperazinyl)butyl)-2 -pyridinecarboxamide (16) and 3-amino-N-(4-(4-(1,2-benzisothiazol-3-yl)-1-piperazinyl)butyl) -2-thiophenecarboxamide (29). Furthermore, these derivatives were found to be much less active in behavioral models predictive of extrapyramidal side effects than in the mouse climbing assay, which predicts antipsychotic activity. Carboxamides 16 and 29 were selected for further evaluation as potential backup compounds to 1.

Animals↗
PubMed1982

Effects of varying inspiratory flow waveform and time in intermittent positive pressure ventilation: pulmonary oedema.

Greyhound dogs were given oleic acid i.v. to induce controlled pulmonary oedema. These animals were then studied using intermittent positive pressure ventilation (IPPV) with four different inspiratory flow waveforms, each at three different inspiratory times, in a fixed respiratory cycle of 4 s at a constant tidal volume. Although there were statistically significant differences in airway and oesophageal pressures between the different waveforms and times, there was little variation in the other physiological parameters studied except for arterial carbon dioxide tension. (PaCO2) which showed statistically significant improvement with reversed ramp and sine wave inputs and at the longer inspiratory time of 2.2s. Venous admixture (Qs/Qt) was also less with the longer inspiratory time of 2.2s.

Animals↗