Phosphoryl transfer by a concerted reaction mechanism in UMP/CMP-kinase

The reaction mechanism of phosphoryl transfer catalyzed by UMP/CMP-kinase from Dictyostelium discoideum was investigated by semiempirical AM1 molecular orbital computations of an active site model system derived from crystal structures that contain a transition state analog or a bisubstrate inhibitor. The computational results suggest that the nucleoside monophosphate must be protonated for the forward reaction while it is unprotonated in the presence of aluminium fluoride, a popular transition state analog for phosphoryl transfer reactions. Furthermore, a compactification of the active site model system during the reaction and for the corresponding complex containing AlF3 was observed. For the active site residues that are part of the LID domain, conformational flexibility during the reaction proved to be crucial. On the basis of the calculations, a concerted phosphoryl transfer mechanism is suggested that involves the synchronous shift of a proton from the monophosphate to the transferred PO3-group. The proposed mechanism is thus analogous to the phosphoryl transfer mechanism in cAMP-dependent protein kinase that phosphorylates the hydroxyl groups of serine residues.     

Experimental manipulation of queen number affects colony sex ratio investment in the highly polygynous ant Formica exsecta

In polygynous (multiple queens per nest) ants, queen dispersal is often limited with young queens being recruited within the parental colony. This mode of dispersal leads to local resource competition between nestmate queens and is frequently associated with extremely male-biased sex ratios at the population level. The queen-replenishment hypothesis has been recently proposed to explain colony sex ratio investment under such conditions. It predicts that colonies containing many queens (subject to high local resource competition) should only produce males, whereas colonies hosting few queens (reduced or no local resource competition) should produce new queens in addition to males. We experimentally tested this hypothesis in the ant Formica exsecta by manipulating queen number over three consecutive years in 120 colonies of a highly polygynous population. Queens were transferred from 40 colonies into another 40 colonies while queen number was not manipulated in 40 control colonies. Genetic analyses of worker offspring revealed that our treatment significantly changed the number of reproductive queens. The sex ratio of colonies was significantly different between treatments in the third breeding season following the experiment initiation. We found that, as predicted by the queen-replenishment hypothesis, queen removal resulted in a significant increase in the proportion of colonies that produced new queens. These results provide the first experimental evidence for the queen-replenishment hypothesis, which might account for sex ratio specialization in many highly polygynous ant species.     

Possible role of eclosion rhythm in mediating the effects of light-dark environments on pre-adult development in <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

Background  

In insects, circadian clocks have been implicated in affecting life history traits such as pre-adult development time and adult lifespan. Studies on the period (per) mutants of Drosophila melanogaster, and laboratory-selected lines of Bactrocera cucurbitae suggested a close link between circadian clocks and development time. There is a possibility of clock genes having pleiotropic effects on clock period and pre-adult development time. In order to avoid such pleiotropic effects we have used wild type flies of same genotype under environments of different periodicities, which phenotypically either speeded up or slowed down the eclosion clock of D. melanogaster.     

Auto-antibodies to the receptor tyrosine kinase MuSK in patients with myasthenia gravis without acetylcholine receptor antibodies

Myasthenia gravis (MG) is an antibody-mediated autoimmune disease of the neuromuscular junction. In approximately 80% of patients, auto-antibodies to the muscle nicotinic acetylcholine receptor (AChR) are present. These antibodies cause loss of AChR numbers and function, and lead to failure of neuromuscular transmission with muscle weakness. The pathogenic mechanisms acting in the 20% of patients with generalized MG who are seronegative for AChR-antibodies (AChR-Ab) have not been elucidated, but there is evidence that they also have an antibody-mediated disorder, with the antibodies directed towards another, previously unidentified muscle-surface-membrane target. Here we show that 70% of AChR-Ab-seronegative MG patients, but not AChR-Ab-seropositive MG patients, have serum auto-antibodies against the muscle-specific receptor tyrosine kinase, MuSK. MuSK mediates the agrin-induced clustering of AChRs during synapse formation, and is also expressed at the mature neuromuscular junction. The MuSK antibodies were specific for the extracellular domains of MuSK expressed in transfected COS7 cells and strongly inhibited MuSK function in cultured myotubes. Our results indicate the involvement of MuSK antibodies in the pathogenesis of AChR-Ab-seronegative MG, thus defining two immunologically distinct forms of the disease. Measurement of MuSK antibodies will substantially aid diagnosis and clinical management.     

Protein--protein docking of electron transfer complexes: cytochrome c oxidase and cytochrome c

Electron transferring protein complexes form only transiently and the crystal structures of electron transfer protein--protein complexes involving cytochrome c could so far be determined only for the pairs of yeast cytochrome c peroxidase (CcP) with iso-1-cytochrome c (iso-1-cyt c) and with horse heart cytochrome c (cyt c). This article presents models from computational docking for complexes of cytochrome c oxidase (COX) from Paracoccus denitrificans with horse heart cytochrome c, and with its physiological counterpart cytochrome c552 (c552). Initial docking is performed with the FTDOCK program, which permits an exhaustive search of translational and rotational space. A filtering procedure is then applied to reduce the number of complexes to a manageable number. In a final step of structural and energetic refinement, the complexes are optimized by rigid-body energy minimization with the molecular mechanics package CHARMM. This methodology was first tested on the CcP:iso-1-cyt c complex, in which the complex with the lowest CHARMM energy has an RMSD from the crystal structure of only 1.8 A (C(alpha) carbon atoms). Notably, the crystal conformation has an even lower energy. The same procedure was then applied to COX:cyt c and COX:c552. The lowest-energy COX:cyt c complex is very similar to a docking model previously described for the complex of bovine cytochrome c oxidase with horse heart cytochrome c. For the COX:c552 complex, cytochrome c552 is found in two different orientations, depending on whether it is docked against COX from a two-subunit or from a four-subunit crystal structure, respectively. Both conformations are discussed critically in the light of the available experimental data.     

Seasonality in water related intestinal disease in Guatemala

Field studies in two rural communities in the Pacific lowlands have been in process since 1973 to evaluate the relationship between environmental improvements, particularly a piped water supply, and the prevalence of diarrheal diseases. An initial appraisal of the data indicates that diarrheal diseases in the tropics vary with the dry and rainy seasons. However, there are aspects of the relationship between water and diarrheal disease which still require explanation. The field studies are designed to provide further insight into these seasonal influences as well as to variations which are related to epidemic cycles, environmental factors and the range of socio-economic development in these areas.Presented at the Seventh International Biometeorological Congress, 17–23 August 1975, College Park, Maryland, USA.     

Ecdysteroids: A novel class of anabolic agents?

Increasing numbers of dietary supplements with ecdysteroids are marketed as “natural anabolic agents”. Results of recent studies suggested that their anabolic effect is mediated by estrogen receptor (ER) binding. Within this study the anabolic potency of ecdysterone was compared to well characterized anabolic substances. Effects on the fiber sizes of the soleus muscle in rats as well the diameter of C2C12 derived myotubes were used as biological readouts. Ecdysterone exhibited a strong hypertrophic effect on the fiber size of rat soleus muscle that was found even stronger compared to the test compounds metandienone (dianabol), estradienedione (trenbolox), and SARM S 1, all administered in the same dose (5 mg/kg body weight, for 21 days). In C2C12 myotubes ecdysterone (1 µM) induced a significant increase of the diameter comparable to dihydrotestosterone (1 µM) and IGF 1 (1.3 nM). Molecular docking experiments supported the ERβ mediated action of ecdysterone. To clarify its status in sports, ecdysterone should be considered to be included in the class “S1.2 Other Anabolic Agents” of the list of prohibited substances of the World Anti-Doping Agency.