A time-resolved fluoroimmunometric assay for the detection of microcystins, cyanobacterial peptide hepatotoxins

An immunoassay based on the time-resolved fluorometry (TR-FIA) was developed for microcystins, cyanobacterial peptide hepatotoxins. The assay was performed in a competitive mode and it utilised the monoclonal antibodies raised against microcystin-LR, and a europium chelate of microcystin-LR as a competitive antigen. The sensitivity of the assay was 0.1microg/l. The detection method of TR-FIA was compared to a commercially available kit based on the enzyme-linked immunosorbent assay (ELISA). The same level of sensitivity could be obtained with TR-FIA (in a non-optimised system). The simplified method of TR-FIA leads to a shorter analysis time.

Mitotic reorganization of the intermediate filament protein nestin involves phosphorylation by cdc2 kinase

The intermediate filament protein nestin is expressed during early stages of development in the central nervous system and in muscle tissues. Nestin expression is associated with morphologically dynamic cells, such as dividing and migrating cells. However, little is known about regulation of nestin during these cellular processes. We have characterized the phosphorylation-based regulation of nestin during different stages of the cell cycle in a neuronal progenitor cell line, ST15A. Confocal microscopy of nestin organization and (32)P in vivo labeling studies show that the mitotic reorganization of nestin is accompanied by elevated phosphorylation of nestin. The phosphorylation-induced alterations in nestin organization during mitosis in ST15A cells are associated with partial disassembly of nestin filaments. Comparative in vitro and in vivo phosphorylation studies identified cdc2 as the primary mitotic kinase and Thr(316) as a cdc2-specific phosphorylation site on nestin. We generated a phosphospecific nestin antibody recognizing the phosphorylated form of this site. By using this antibody we observed that nestin shows constitutive phosphorylation at Thr(316), which is increased during mitosis. This study shows that nestin is reorganized during mitosis and that cdc2-mediated phosphorylation is an important regulator of nestin organization and dynamics during mitosis.

Production and specificity of mono and polyclonal antibodies against microcystins conjugated through N-methyldehydroalanine

Microcystins (MCs) are a group of closely related toxic cyclic heptapeptides produced by common cyanobacteria (blue-green algae). Their toxicity is associated with specific inhibition of intracellular protein phosphatases type-1 and type-2A (PP1 and PP2A, respectively). We have developed a battery of antibodies to microcystins using chemical modification (aminoethylation) of one of its core amino acids, N-methyl-dehydroalanine. The developed antibodies displayed different reactivities to closely related MCs. Selected monoclonal antibodies were used for quantitative competitive ELISA assays. The analytical sensitivity of these assays was up to 1 ng/ml. Comparison of the developed ELISA tests with HPLC-based measurements of MCs in laboratory and field samples showed a good correspondence between the results yielded by these two methods. The antibodies developed by this technique provide the means for developing extremely sensitive and specific analytical assays for direct measurement of toxins in cyanobacterial or water samples.

Relationship between microtubule dynamics and lamellipodium formation revealed by direct imaging of microtubules in cells treated with nocodazole or taxol

Microtubules (MTs) contribute to the directional locomotion of many cell types through an unknown mechanism. Previously, we showed that low concentrations (<200 nM) of nocodazole or taxol reduced the rate of locomotion of NRK fibroblasts over 60% without altering MT polymer level [Liao et al., 1995: J. Cell Sci. 108:3473-3483]. In this paper, we directly measured the dynamics of MTs in migrating NRK cells injected with rhodamine tubulin and treated with low concentrations of nocodazole or taxol. Both drug treatments caused statistically significant reductions (approx. twofold) in growth and shortening rates and less dramatic effects on rescue and catastrophe transition frequencies. The percent time MTs were inactive (i.e., paused) increased greater than twofold in nocodazole- and taxol-treated cells, while the percent time growing was substantially reduced. Three parameters of MT dynamics were linearly related to the rates of locomotion determined previously: rate of shortening, percent time pausing and percent time growing. The number of MTs that came within 1 microm of the leading edge was reduced in drug-treated cells, suggesting that reduced MT dynamics may affect actin arrays necessary for cell locomotion. We examined two such structures, lamellipodium and adhesion plaques, and found that lamellipodia area was coordinately reduced with MT dynamics. No effect was detected on adhesion plaque density or distribution. In time-lapse recordings, MTs did not penetrate into the lamellipodium of untreated cells, suggesting that MTs affect lamellipodia either through their interaction with factors at the base of the lamellipodium or by releasing factors that diffuse into the lamellipodia. In support of the latter hypothesis, when all MTs were rapidly depolymerized by 20 microM nocodazole, we detected the rapid formation of exaggerated protrusions from the leading edge of the cell. Our results show for the first time a linear relationship between MT dynamics and the formation of the lamellipodium and support the idea that MT dynamics may contribute to cell locomotion by regulating the size of the lamellipodium, perhaps through diffusable factors.

Microcystin-LR toxicodynamics, induced pathology, and immunohistochemical localization in livers of blue-green algae exposed rainbow trout (oncorhynchus mykiss)

With this retrospective study, we investigated the temporal pattern of toxin exposure and pathology, as well as the topical relationship between hepatotoxic injury and localization of microcystin-LR, a potent hepatotoxin, tumor promoter, and inhibitor of protein phosphatases-1 and -2A (PP), in livers of MC-gavaged rainbow trout (Oncorhynchus mykiss) yearlings, using an immunohistochemical detection method and MC-specific antibodies. H&E stains of liver sections were used to determine pathological changes. Nuclear morphology of hepatocytes and ISEL analysis were employed as endpoints to detect the advent of apoptotic cell death in hepatocytes. Trout had been gavaged with lyophilized cyanobacteria (Microcystis aeruginosa, strain PCC 7806) at acutely toxic doses of 5700 microg microcystin (MC) per kg of body weight (bw), as described previously (Tencalla and Dietrich, 1997). Briefly, 3 control and 3 test animal were killed 1, 3, 12, 24, 48, and 72 h after bolus dosing, and livers were fixed and paraffin embedded for histological analysis and later retrospective histochemical analyses. The results of the immunohistochemistry reported here revealed a time dependent, discernible increase in MC-positive staining intensity throughout the liver, clearly not concurring with the kinetics of hepatic PP inhibition observed in the same fish and reported in an earlier publication by Tencalla and Dietrich (1997). After 3 h, marked and increasing MC-immunopositivity was observed in the cytoplasm, as well as the nuclei of hepatocytes. Apoptotic cell death could be detected after 48 h, at the very earliest. These data suggest that accumulation of MC and subsequent changes in cellular morphology, PP inhibition, and hepatocyte necrosis represent the primary events in microcystin induced hepatotoxicity and appear to be associated with the reversible interaction of MC with the PP. In contrast, apoptotic cell death, as demonstrated here, seems to be of only secondary nature and presumably results from the covalent interaction of MC with cellular and nuclear PP as well as other thiol containing cellular proteins.

Manipulation of cells through elastic films

Manipulation of cells in open dishes is often incompatible withpreservation of sterility. A dish covered with an elastic orstretchable latex or plastic film allows manipulation of cellsthrough the film with preservation of sterility of the cultureand the integrity of the film. The latter forms a ;microglove'for the instrument tip. The idea of manipulation through a thintransparent film is also applicable to general surgery, so thatthe surgeon's hand operates through a film and without a glove.

Dynamics of gap junctions observed in living cells with connexin43-GFP chimeric protein

To study the aggregation of cell-to-cell channels into gap junctions at individual cell-cell contacts, we transfected cells with an expression vector for a chimeric protein composed of the cell-to-cell channel protein connexin43 and a green fluorescent protein. The chimeric channel protein was visualized in the fluorescence microscope and was found to form gap junctions at the cell-cell contacts just like wild-type connexin43. Cells expressing the chimeric protein had functional cell-to-cell channels. Using timelapse videomicroscopy on live cells we observed individual gap junctions over long periods and recorded the time course of aggregation of the chimeric channel protein into gap junctions at newly formed cell-cell contacts. We found that individual small gap junctions were very dynamic, moving about or becoming assembled and disassembled in the course of minutes. Larger gap junctions were more stable than small punctate ones. In control condition, stable new gap junctions were not formed during observation times of 30 min or longer. But at elevated levels of cyclic adenosine monophosphate, the chimeric channel protein began aggregating at new junctions 5-10 minutes after cell-cell contact and continued to concentrate there for at least one hour. Also already established junctions grew in size. The fluorescent chimeric channel protein will be an excellent tool to investigate the regulation of trafficking of connexin from and to the membrane and the mechanism of connexin channel aggregation into gap junctions.

Focal adhesion motility revealed in stationary fibroblasts

Focal adhesions (FAs) are clustered integrins and associated proteins that mediate cell adhesion and signaling. A green fluorescent protein-beta1 integrin chimera was used to label FAs in living cells. In stationary cells, FAs were highly motile, moving linearly for several plaque lengths toward the cell center. FA motility was independent of cell density and resulted from contraction of associated actin fibers. In migrating cells, FAs were stationary and only moved in the tail. FA motility in stationary cells suggests that cell movement may be regulated by a clutch-like mechanism by which the affinity of integrins to substrate may be altered in response to migratory cues.

Structure of ribosomal protein L30 from Thermus thermophilus at 1.9 A resolution: conformational flexibility of the molecule

The crystal structure of ribosomal protein L30 from the extreme thermophilic bacterium Thermus thermophilus has been determined at 1. 9 A resolution. The crystals are trigonal and belong to space group P3(2)21, with unit-cell parameters a = b = 63.5, c = 77.8 A, alpha = beta = 90, gamma = 120 degrees and two molecules per asymmetric unit. The structure was solved by the molecular-replacement method with AMoRe and refined with X-PLOR to an R value of 20.3% and an R(free) of 25.3% in the resolution range 8-1.9 A. Detailed analyses of the structures of the two molecules in the asymmetric unit and comparison of T. thermophilus L30 structure with the structure of homologous L30 from Bacillus stearothermophilus reveal two flexible regions at opposite ends of the rather elongated molecule. Such flexibility could be important for the protein fitting in the ribosome. A comparison with B. stearothermophilus L30 shows a higher number of salt bridges and unbound positively charged residues and an increased accessible hydrophobic area on the surface of T. thermophilus L30. This could contribute to the stability of both the extreme thermophile protein and the ribosome as a whole.

Self-organizing molecular networks

Strong diffusional mixing and short delivery times typical for micrometer and sub-micrometer reaction volumes lead to a special situation where the turnover times of individual enzyme molecules become the largest characteristic time scale of the chemical kinetics. Under these conditions, populations of cross-regulating allosteric enzymes form molecular networks that exhibit various kinds of self-organized coherent collective dynamics.

Crystal structure of mistletoe lectin I from Viscum album

The crystal structure of the ribosome-inactivating protein (RIP) mistletoe lectin I (ML-I) from Viscum album has been solved by molecular replacement techniques. The structure has been refined to a crystallographic R-factor of 24.5% using X-ray diffraction data to 2.8 A resolution. The heterodimeric 63-kDa protein consists of a toxic A subunit which exhibits RNA-glycosidase activity and a galactose-specific lectin B subunit. The overall protein fold is similar to that of ricin from Ricinus communis; however, unlike ricin, ML-I is already medically applied as a component of a commercially available misteltoe extract with immunostimulating potency and for the treatment of human cancer. The three-dimensional structure reported here revealed structural details of this pharmaceutically important protein. The comparison to the structure of ricin gives more insights into the functional mechanism of this protein, provides structural details for further protein engineering studies, and may lead to the development of more effective therapeutic RIPs.

Novel features of intermediate filament dynamics revealed by green fluorescent protein chimeras

In order to study the dynamic behavior of intermediate filament networks in living cells, we have prepared constructs fusing green fluorescent protein to intermediate filament proteins. Vimentin fused to green fluorescent protein labeled the endogenous intermediate filament network. We generated stable SW13 and NIH3T3 cell lines that express an enhanced green fluorescent protein fused to the N-terminus of full-length vimentin. We were able to observe the dynamic behavior of the intermediate filament network in these cells for periods as long as 4 hours (images acquired every 2 minutes). In both cell lines, the vimentin network constantly moves in a wavy manner. In the NIH3T3 cells, we observed extension of individual vimentin filaments at the edge of the cell. This movement is dependent on microtubules, since the addition of nocodazole stopped the extension of the intermediate filaments. Injection of anti-IFA causes the redistribution or ‘collapse’ of intermediate filaments. We injected anti-IFA antibodies into NIH3T3 cells stably expressing green fluorescent protein fused to vimentin and found that individual intermediate filaments move slowly towards the perinuclear area without obvious disassembly. These results demonstrate that individual intermediate filaments are translocated during the collapse, rather than undergoing disassembly-induced redistribution. Injections of tubulin antibodies disrupt the interactions between intermediate filaments and stable microtubules and cause the collapse of the vimentin network showing that these interactions play an important role in keeping the intermediate filament network extended. The nocodazole inhibition of intermediate filament extension and the anti-IFA microinjection experiments are consistent with a model in which intermediate filaments exhibit an extended distribution when tethered to microtubules, but are translocated to the perinuclear area when these connections are severed.

Primary structure and molecular modeling of mistletoe lectin I from Viscum album

The first three-dimensional structure of the ribosome inactivating protein mistletoe lectin I (ML-I) from Viscum album has been modeled on the basis of the X-ray structure of castor bean ricin from Ricinus communis. The relative high sequence homology and conserved secondary structure enabled accurate modeling. The 196 sequence changes between ML-I and ricin could be accomodated with only little pertubation in the main chain folding. A close comparison of the primary structures of ML-I and ricin is given and the effects of the sequence changes are elucidated on the basis of the modeled three-dimensional structure. Differences have been identified in the vicinity of the active site, in the high affinity galactose binding site and in the interface between the A and B chains, which might account for the reduced cytotoxicity of ML-I.

Self-organizing molecular networks

Strong diffusional mixing and short delivery times typical for micrometer and sub-micrometer reaction volumes lead to a special situation where the turnover times of individual enzyme molecules become the largest characteristic time scale of the chemical kinetics. Under these conditions, populations of cross-regulating allosteric enzymes form molecular networks that exhibit various kinds of self-organized coherent collective dynamics.

Transition from molecular chaos to coherent spiking of enzymic reactions in small spatial volumes

Theoretical study of an irreversible enzymic reaction with allosteric product activation reveals that, in small spatial volumes, it can undergo a transition to coherent spiking regime characterized by the presence of strong correlations between reaction events and the states of individual enzyme molecules.

Microscopic self-organization in living cells: a study of time matching

Biochemical subsystems of a living cell may operate with only a few thousand enzyme molecules and their response can be triggered by the entrance of individual molecules of a certain species. This mode of operation is not described by classical chemical kinetics, which deals with large numbers of reacting molecules. Theoretical estimates for the characteristic times of enzymic reactions in small cells and cellular compartments show that any two macromolecules within a micrometer-size volume meet each other each second and that the transit time, required for a mediator molecule to meet a target enzyme, is comparable to the duration of a catalytic round for a single enzyme molecule. When these conditions are satisfied, an enzymic subsystem represents a coherent molecular network with persistent strong temporal correlations between the catalytic events of individual enzyme molecules.

Fluctuations in living cells and intracellular traffic

Theoretical estimates reveal the presence of strong thermal hydrodynamic fluctuations in the cytoplasm of living cells. It is suggested here that these intensive fluctuations may be utilized by biological vesicles inside the cells to produce their directed drift to the targets. A possible mechanism of partial rectification of thermal fluctuations is based on the effect of active navigation: i.e. on the controlled response of vesicles to velocity fluctuations.