X-ray structure of recombinant horse L-chain apoferritin at 2.0 Å resolution: implications for stability and function

The X-ray structure of recombinant horse L-chain (rL) apoferritin, solved at 2.0?Å resolution with a final R factor of 17.9%, gives evidence that the residue at position 93 in the sequence is a proline and not a leucine, as found in earlier sequencing studies. The structure is isomorphous with other apoferritin structures, and we thus draw particular attention to those structural features which can be related to the stability and function of the protein. Analysis of hydrogen bonding and salt bridge interactions shows that dimers and tetramers are the most stable molecular entities within the protein shell: a result confirming earlier biophysical experiments. The stability of horse rL apoferritin to both dissociation into subunits at acidic pH values and to complete unfolding in guanidine chloride solutions is compared with that of other apoferritins. This emphasizes the role played by the salt bridge in the stability of this protein family. The horse rL apoferritin is significantly more resistant to denaturation than horse spleen ferritin, which in turn is more resistant than any human rH apoferritins, even those for which a salt bridge is restored. Finally, this structure determination not only establishes that a preformed pocket exists in L-chain apoferritin, at a site known to be able to bind porphyrin, but also underlines the particular function of a cluster of glutamic acids (E53, E56, E57 and E60) located at the entrance of this porphyrin-binding pocket.     

Marine nematodes of the family Draconematidae (Nemata): a synthesis with phylogenetic relationships

The family Draconematidae is reviewed. Diagnoses of all taxa are updated or emended, basedupon an evaluation of diagnostic features. Aphylogenetic analysis at the genus level based onparsimony suggested that Tenuidraconema belongsto the Draconematinae. A new genus Bathychaetosoma is erected to accomodate B.uchidai (Kito, 1983). It is characterized by acephalic region with a smooth, non-thickened cuticleand numerous cephalic adhesion tubes located posteriorto the head region and extending over more than twohead diameters along the cervical region.     

Modeling of adaptations to physical training by using a recursive least squares algorithm

Busso, Thierry, Christian Denis, Régis Bonnefoy,André Geyssant, and Jean-René Lacour. Modeling ofadaptations to physical training by using a recursive least squaresalgorithm. J. Appl. Physiol. 82(5):1685-1693, 1997.The present study assesses the usefulnessof a systems model with time-varying parameters for describing theresponses of physical performance to training. Data for two subjectswho undertook a 14-wk training on a cycle ergometer were used to testthe proposed model, and the results were compared with a model withtime-invariant parameters. Two 4-wk periods of intensive training wereseparated by a 2-wk period of reduced training and followed by a 4-wkperiod of reduced training. The systems input ascribed to the trainingdoses was made up of interval exercises and computed in arbitraryunits. The systems output was evaluated one to five times per week byusing the endurance time at a constant workload. The time-invariantparameters were fitted from actual performances by using the leastsquares method. The time-varying parameters were fitted by using arecursive least squares algorithm. The coefficients of determinationr² were 0.875 and0.879 for the two subjects using the time-varying model, higher thanthe values of 0.682 and 0.666, respectively, obtained with thetime-invariant model. The variations over time in the model parametersresulting from the expected reduction in the residuals appearedgenerally to account for changes in responses to training. Such a modelwould be useful for investigating the underlying mechanisms ofadaptation and fatigue.

     

RANDOM AMPLIFIED POLYMORPHIC DNA (RAPD) AND PARSIMONY METHODS

Abstract — Random amplified polymorphic DNA (RAPD) data possess a number of undesirable features for parsimony analysis. These features include their non-codominant inheritance, their anonymous nature, their different (a)symmetrical transformation probabilities, and their possible GC priming bias. As a consequence, no single parsimony method seems appropriate for RAPD data. Moreover, the presence/absence coding of RAPDs is equivalent to the invalid independent allele model for allozymes. These issues are discussed and the way in which parsimony analysis of RAPDs can be misleading is illustrated.     

Glutamine synthetase (GS) expression is reduced in senile dementia of the Alzheimer type

Glutamine synthetase (GS), a metabolic marker of the mature astrocyte, was investigated in the temporal neocortex of postmortem brain samples of 8 cases, either not demented or affected by senile dementia of the Alzheimer type. A negative correlation between the GS protein level and the density of both classical A4 deposits and senile plaques was evidenced. Such a correlation for GS underlies a dysfunction of the astroglial metabolism and particularly of the glutamate and ammonia neutralization. Since GS is sensitive to oxidative lesioning, the changes in GS level that were observed, occurring at the posttranslational stage, might reflect oxidative damage and have severe consequences on the pathological cascade of events.     

Global scale patterns of fish species richness in rivers

Explanations of spatial and temporal variation in species richness is a central theme in community ecology Until recently, most research has focused on small-scale phenomena, often emphasizing on local environmental factors and, thus, poorly reflecting large-scale processes that organize species richness In this paper, we analyze variations in species richness of indigeneous freshwater fish on a worldwide scale We show that factors related to species-area and species-energy theories statistically explain most of the variation in freshwater fish species richness across continents Historical events supposed to influence present distributions offish are of little assistence in explaining variations in fish species richness at the global scale Our model, which uses easily measured factors, should also be of practical value to aquatic conservation biology and natural resource management     

Conformational change in yeast tRNAAsp

The structure of yeast tRNA^Asp in aqueous solutions has been analyzed in the light of results obtained from Raman spectra recorded at from 5 to 82°C and compared to those of tRNA^Phe. Firm evidence is given of a reversible conformation transition for tRNA^Asp at 20°C. This transition is observed for the first time in the tRNA series. The low-temperature conformation appears to have a more regular ribose–phosphate backbone and a more effective G base-stacking. This conformational change, which occurs essentially in the D loop, could be connected to the existence of two (A and B) crystal forms obtained depending on crystallization conditions. The melting temperatures, which are different for each base stacking in tRNA^Asp, lie in a range of about 70°C, much higher than for tRNA^Phe. This fact is interpreted by a higher ratio of G-C base pairs in tRNA^Asp.     

Yeast transfer RNAasp: a new high-resolution x-ray diffracting crystal form of a transfer RNA.

Systematic crystallization studies on brewer's yeast aspartic acid transfer RNA have yielded different crystal forms, one of them diffracting to 3 Å resolution. The high resolution crystal form is orthorhombic ($\text{C222}{}_1\text{, a = 61}\text{A}\text{?}\text{, b = 68}\text{A}\text{?}\text{, c = 148}\text{A}\text{?}$ with one molecule per asymmetric unit) and is stable for over four days under X-rays.     

A neutron investigation of yeast valyl-tRNA synthetase interaction with tRNAs.

A new way of studying RNA-protein complexes, using neutron small angle scattering in solution, is described and was applied in the case of the system, yeast valyl-tRNA synthetase, interacting with its cognate and non cognate yeast tRNAs. It was shown that, when limited amounts of tRNA (either cognate or non cognate) are added to valyl-tRNA synthetase, a complex consisting of two enzyme molecules and one tRNA molecule is first formed. It is subsequently dissociated to a one to one complex when more tRNA is present in the solution. The association curve shows a maximum for a molecular ratio, enzyme over tRNA, equal to 2.