Vulnerability to predation and physiological stress responses of experimentally descaled juvenile chinook salmon,Oncorhynchus tshawytscha

Synopsis Juvenile salmonids,Oncorhynchus spp., commonly encounter conditions (e.g., during hatchery release and dam passage) that result in damage to the skin, scale, and slime complex. We conducted laboratory experiments to determine if descaling of juvenile chinook salmon,O. tshawytscha, increased their vulnerability to predation, and to assess the physiological stress responses elicited by descaling. Salmon were experimentally descaled on either 10% or 20% of their total body area. When offered equal numbers of control and descaled juvenile chinook salmon, northern squawfish,Ptychocheilus oregonensis, did not consume significantly more of either prey type (48–60% of consumed prey were descaled). Juvenile chinook salmon descaled on 10% of their body area did show significant physiological stress responses, however. Mean concentrations of plasma cortisol peaked 1 h after descaling, and returned to control levels by 12 h. Plasma glucose peaked 3 h post-treatment and remained elevated for 24 h. Plasma lactate increased immediately following treatment and returned to undisturbed control levels by 3 h. The osmoregulatory response of plasma potassium was highly variable, but plasma sodium decreased immediately and remained low for 24 h. The observed physiological responses suggest that descaling of juvenile chinook salmon could result in decreased resistance to disease and other stressors encountered in the field, possibly leading to reduced performance capacity and lowered survival.     

Characteristics of Mycoplasma hominis adhesion.

Mycoplasma hominis, a human pathogen, has previously been observed to bind to sulfatide separated on thin-layer chromatograms. It has not been demonstrated, however, that the binding is not simply a nonspecific ionic interaction. The ability of a low-passage patient isolate of M. hominis to adhere to glycoconjugates other than sulfatide and the characteristics of its binding to sulfatide were studied. Mycoplasmas were found to bind strongly and specifically in a temperature- and dose-dependent manner to only sulfatide of all of the glycolipids and glycoproteins tested. The avidity and specificity of binding, as well as the ability to inhibit the interaction specifically, suggest that the receptors to which M. hominis binds, particularly in the human urogenital tract, from which it is frequently isolated, are primarily, if not solely, sulfated glycolipids.     

A Simple and Safe Device for Spreading Ultrathin Sections with Chloroform

A simple and safe device for spreading ultrathin sections for electron microscopy is described. The use of this device minimizes the release of chloroform vapor during section spreading.     

Complete genome sequences of cellular life forms: glimpses of theoretical evolutionary genomics

The availability of complete genome sequences of cellular life forms creates the opportunity to explore the functional content of the genomes and evolutionary relationships between them at a new qualitative level. With the advent of these sequences, the construction of a minimal gene set sufficient for sustaining cellular life and reconstruction of the genome of the last common ancestor of bacteria, eukaryotes, and archaea become realistic, albeit challenging, research projects. A version of the minimal gene set for modern-type cellular life derived by comparative analysis of two bacterial genomes, those of Haemophilus influenzae and Mycoplasma genitalium, consists of ∼250 genes. A comparison of the protein sequences encoded in these genes with those of the proteins encoded in the complete yeast genome suggests that the last common ancestor of all extant life might have had an RNA genome.     

Molecular analysis of the feline immunodeficiency virus protease: generation of a novel form of the protease by autoproteolysis and construction of cleavage-resistant proteases.

The feline immunodeficiency virus (FIV) protease is essential for virion maturation and subsequent viral replication in that it cleaves the Gag and Gag/Pol polyproteins at eight sites to release the respective structural proteins and enzymes. During purification of a recombinant FIV protease (PR), we noted that it underwent autoproteolysis (autolysis) to give discrete cleavage products. These additional PR cleavage sites were defined using N-terminal amino acid sequence analysis and mass spectrometry. Protease breakdown products were also found in FIV virions and were of the same apparent molecular weights as the in vitro autolysis products. Four primary PR autolysis sites were blocked via substitution of either the P1 amino acid with a beta-branched amino acid or the P1' amino acid with lysine. Cleavage-resistant PRs which had Km and k(cat) values similar to those of FIV PR were constructed. An autolysis time course determined that blocking all four primary autolysis sites yielded a cleavage-resistant PR which was enzymatically stable. Concomitant with autolysis is the generation of an N-terminally truncated form of the PR (Thr6/PR) which has enhanced stability with respect to that of FIV PR. A structural basis for the Thr6/PR activity is presented, as are the possible roles of autolysis in the viral replication cycle.     

Homology modeling of histidine-containing phosphocarrier protein and eosinophil-derived neurotoxin: Construction of models and comparison with experiment

Homology modeling methods have been used to construct models of two proteins—the histidine-containing phosphocarrier protein (HPr) from Mycoplasma capricolum and human eosinophil-derived neurotoxin (EDN). Comparison of the models with the subsequently determined X-ray crystal structures indicates that the core regions of both proteins are reasonably well reproduced, although the template structures are closer to the X-ray structures in these regions—possible enhancements are discussed. The conformations of most of the side chains in the core of HPr are well reproduced in the modeled structure. As expected, the conformations of surface side chains in this protein differ significantly from the X-ray structure. The loop regions of EDN were incorrectly modeled—reasons for this and possible enhancements are discussed. © 1995 Wiley-Liss, Inc.     

Three-dimensional structure of ectatomin from Ectatomma tuberculatum ant venom

Summary Two-dimensional ¹H NMR techniques were used to determine the spatial structure of ectatomin, a toxin from the venom of the ant Ectatomma tuberculatum. Nearly complete proton resonance assignments for two chains of ectatomin (37 and 34 amino acid residues, respectively) were obtained using 2D TOCSY, DQF-COSY and NOESY experiments. The cross-peak volumes in NOESY spectra were used to define the local structure of the protein and generate accurate proton-proton distance constraints employing the MARDIGRAS program. Disulfide bonds were located by analyzing the global fold of ectatomin, calculated with the distance geometry program DIANA. These data, combined with data on the rate of exchange of amide protons with deuterium, were used to obtain a final set of 20 structures by DIANA. These structures were refined by unrestrained energy minimization using the CHARMm program. The resulting rms deviations over 20 structures (excluding the mobile N- and C-termini of each chain) are 0.75 ? for backbone heavy atoms, and 1.25 ? for all heavy atoms. The conformations of the two chains are similar. Each chain consists of two α-helices and a hinge region of four residues; this forms a hairpin structure which is stabilized by disulfide bridges. The hinge regions of the two chains are connected together by a third disulfide bridge. Thus, ectatomin forms a four-α-helical bundle structure.