Analysis of the structural specificity of the lactose permease toward sugars

The sugar specificity properties of the lactose permease were investigated. Free galactose was shown to competitively inhibit the lactose permease yielding a Ki value of 7.4 mM. This value was severalfold higher than the observed Km for lactose (1.3 mM). A variety of other monosaccharides also showed significant inhibition of lactose transport. With regard to -OH groups along the galactose ring it appears that the relative importance is OH-3 greater than OH-4 greater than OH-6 greater than OH-2 greater than OH-1. In general, galactosides with alpha-linkages exhibited significantly higher affinities compared with their beta-linked counterparts. An optimal size for the aglycone portion of the galactoside was reached with aglycones containing hexose residues or a benzene ring. The preferred size of the aglycone appears to be hexose, benzene ring greater than methyl group greater than no aglycone much greater than disaccharide greater than trisaccharide. However, neither the specific structure of the aglycone nor its relative hydrophobicity appeared to be important factors in permease recognition. For example, the hydrophobic beta-nitrophenyl-galactosides had lower affinities compared with lactose (a beta-galactoside), whereas the alpha-nitrophenylgalactosides generally had higher affinities compared with melibiose (an alpha-galactoside). In addition, no consistent preference was seen when considering the location of the nitro group on the benzene ring. From this work, a model is presented which depicts the binding of galactosides to the lactose permease.     

Thiol-sensitive genes of Escherichia coli.

The effect of 1-thioglycerol on the expression of genes of Escherichia coli was investigated. Pulse-labeled proteins from aerobically growing, 1-thioglycerol-treated E. coli were separated by two-dimensional gel electrophoresis, and their radioactivities were compared with those of identical proteins from nontreated cells. The first 10 min of exposure to thiol stimulated the synthesis of 10% of the observed proteins and inhibited the production of 16% of the proteins. After 30 min of growth with thiol, the synthesis of 44% of the observed proteins was inhibited and synthesis of 18% of the proteins was stimulated. In general, the expression of genes of carbohydrate metabolism, amino acid metabolism, and protein biosynthesis were inhibited, while nucleic acid synthetic and repair gene expressions showed mixed responses. Synthesis of transport proteins was not affected. Transient stimulation of oxidative-stress proteins and sustained stimulation of the expressions of trxB, ompA, and ompB genes and those of several unidentified gene products were also observed. Whether these complex responses merely reflect adjustments by cellular subsystems to a suddenly reducing environment or whether they are manifestations of a reductive-stress regulon will have to await genetic analysis of this phenomenon.     

A Model of Glutamate Neurotoxicity and Mechanisms of the Development of the Typical Pathological Process

Biophysics - A glutamate model of stroke was analyzed from the standpoint of the development of a typical pathological process that is thought to occur when major regulatory mechanisms are...     

The utility of wing morphometrics for assigning type specimens to cryptic bumblebee species

Since the beginning of taxonomy, species have been described based on morphology, but the advent of using semio-chemicals and genetics has led to the discovery of cryptic species (i.e. morphologically similar species). When a new cryptic species is described, earlier type specimens have to be re-evaluated, although this process can be challenging as only nondestructive methods ought to be used in order to preserve the integrity of the type specimens. Methods should allow comparison with recently collected specimens clustered based on chemical, ethological and/or genetic traits with old specimens (i.e. type specimens) where only morphological traits are available. Here we develop a method based on geometric morphometric analyses of wing shape for a taxonomically challenging group of bumblebees, the subgenus Alpinobombus Skorikov. We consider nine monophyletic taxa (including several cryptic species) to assess the accuracy of this method to discriminate the taxa based on their wing shape and then to attribute type specimens using a leave-one-out cross-validation procedure. We show that, for these bees, wing shape is taxon-specific, except for two sister taxa for which the species status is still debated. Moreover, for most of the taxa, type specimens were correctly attributed with high posterior probabilities of attribution, except for a few type specimens corresponding to the same two sister taxa where taxa delimitation based on wing shape was previously the subject of discussion. Our study highlights the potential of geometric morphometric analyses to help in the re-attribution of type specimens when the existence of cryptic species is revealed.     

Harder,better, faster,stronger: Weapon size is more sexually dimorphic than weapon biomechanical components in two freshwater anomuran species

Sexual selection influences the evolution of morphological traits that increase the likelihood of monopolizing scarce resources. When such traits are used during contests, they are termed weapons. Given that resources are typically linked to monopolizing mating partners, theory expects only males to bear weapons. In some species, however, females also bear weapons, although typically smaller than male weapons. Understanding why females bear smaller weapons can thus help us understand the selective pressures behind weapon evolution. However, most of our knowledge comes from studies on weapon size, while the biomechanics of weapons, such as the size of the muscles, efficiency, and shape are seldom studied. Our goal was to test if the theoretical expectations for weapon size sexual dimorphism also occur for weapon biomechanics using two aeglid crab species. Males of both species had larger claws which were also stronger than female claws. Male claws were also more efficient than females' claws (although we used only one species in this analysis). For weapon shape, though, only one species differed in the mean claw shape. Regarding scaling differences, in both species, male claws had higher size scaling than females, while only one species had a higher shape scaling. However, male weapons did not have higher scaling regarding strength and efficiency than females. Thus, males apparently allocate more resources in weapons than females, but once allocated, muscle and efficiency follow a similar developmental pathway in both sexes. Taken together, our results show that sexual dimorphism in weapons involves more than differences in size. Shape differences are especially intriguing because we cannot fully understand its causes. Yet, we highlight that such subtle differences can only be detected by measuring and analysing weapon shape and biomechanical components. Only then we might better understand how weapons are forged.