Charge substitution shows that repulsive electrostatic interactions impede the oligomerization of Alzheimer amyloid peptides

The strong pH dependence of A beta oligomerization could arise from favorable intermolecular charge-charge interactions between His and carboxylate groups, or, alternatively, by mutual electrostatic repulsion of peptide molecules. To test between these two possibilities, the pH dependence of the oligomerization of A beta and three charge substitution variants with Asp, Glu and His substituted by Ala is measured. All four peptides oligomerize, as detected by thioflavin T fluorescence, turbidity, and amyloid fibril formation; therefore, specific charge-charge interactions are nonessential for oligomerization. The strong negative correlation between net charge and oligomerization indicates that electrostatic repulsion between A beta monomers impedes their association.     

Enhanced plasminogen activation by staphylokinase in the presence of streptokinase beta/betagamma domains: plasminogen kringles play a role

Presence of isolated beta or betagamma domains of streptokinase (SK) increased the catalytic activity of staphylokinase (SAK)-plasmin (Pm) complex up to 60%. In contrast, fusion of SK beta or betagamma domains with the C-terminal end of SAK drastically reduced the catalytic activity of the activator complex. The enhancement effect mediated by beta or betagamma domain on Pg activator activity of SAK-Pm complex was reduced greatly (45%) in the presence of isolated kringles of Pg, whereas, kringles did not change cofactor activity of SAK fusion proteins (carrying beta or betagamma domains) significantly. When catalytic activity of SAK-microPm (catalytic domain of Pm lacking kringle domains) complex was examined in the presence of isolated beta and betagamma domains, no enhancement effect on Pg activation was observed, whereas, enzyme complex formed between microplasmin and SAK fusion proteins (SAKbeta and SAKbetagamma) displayed 50-70% reduction in their catalytic activity. The present study, thus, suggests that the exogenously present beta and betagamma interact with Pg/Pm via kringle domains and elevate catalytic activity of SAK-Pm activator complex resulting in enhanced substrate Pg activation. Fusion of beta or betagamma domains with SAK might alter these intermolecular interactions resulting in attenuated functional activity of SAK.     

A problem in multivariate analysis of codon usage data and a possible solution

Multivariate analyses are often used to identify major trends of variation in synonymous codon usage among genes. These analyses need to be performed on properly normalized codon usage data to avoid biases masking this synonymous variation, i.e., gene length, amino acid usage, and codon degeneracy; however, previous studies have failed to do so. In this paper, we demonstrate that the use of alternative normalized data (called 'relative adaptiveness' in the literature) can avoid all these biases and furthermore, can identify more trends of variation among genes, including GC-ending codon usage, GT-ending codon usage, and gene expression level.     

Dissection of Escherichia coli glutamate 5-kinase: functional impact of the deletion of the PUA domain

Glutamate 5-kinase (G5K) catalyzes the controlling first step of the synthesis of the osmoprotective amino acid proline, which feed-back inhibits G5K. Microbial G5K generally consists of one amino acid kinase (AAK) and one PUA (named after pseudo uridine synthases and archaeosine-specific transglycosylases) domain. To investigate the role of the PUA domain, we have deleted it from Escherichia coli G5K. We show that wild-type G5K requires free Mg for activity, it is tetrameric, and it aggregates to higher forms in a proline-dependent way. G5K lacking the PUA domain remains tetrameric, active, and proline-inhibitable, but the Mg requirement and the proline-triggered aggregation are greatly diminished and abolished, respectively, and more proline is needed for inhibition. We propose that the PUA domain modulates the function of the AAK domain, opening the way to potential PUA domain-mediated regulation of G5K; and that this domain moves, exposing new surfaces upon proline binding.     

The role of firefly luciferase C-terminal domain in efficient coupling of adenylation and oxidative steps

The N-terminal domain (N-domain) of the firefly luciferase from Photinus pyraris has weak luminescence activity, and shows a unique light emitting profile with very long rise time of more than several minutes. Through a sensitive assay of the reaction intermediate luciferyl-adenylate (LH2-AMP), we found that the slow increase in the N-domain luminescence faithfully reflected the concentration of dissociated LH2-AMP. No such correlation was observed for wild-type or mutant enzymes with short rise time, except one with longer rise time. The results suggest that the C-terminal domain plays an indispensable role in efficiently coupling adenylation and oxidative steps.     

Angiotensin II induces tyrosine nitration and activation of ERK1/2 in vascular smooth muscle cells

Angiotensin II (Ang II) induces a prominent and sustained nitration and activation of ERK1/2 in rat vascular smooth muscle cells, both mediated via AT1 receptor. Nitration and activation was also shown for recombinant non-activated extracellular signal-regulated kinase (ERK) and MEK. Nitration and phosphorylation of ERK1/2 by Ang II was significantly inhibited by NAD(P)H inhibitors and scavengers of oxygen and nitrogen reactive species and completely blocked by a selective inducible nitric-oxide synthase inhibitor. MEK inhibitor U0126 did not affect ERK nitration but completely blocked activation. These data indicate that Ang II nitrates and activates ERK1/2 via a reactive species-sensitive pathway.     

CHIP interacts with heat shock factor 1 during heat stress

Heat shock factor 1 (HSF1) is a major transactivator of heat shock genes in response to stress and mediates cell protection against various harmful conditions. In this study, we identified the interaction of CHIP (carboxyl terminus of the heat shock cognate protein 70-interacting protein) with the N-terminus of HSF1. Using GST full-down assay, we found that CHIP directly interacts with C-terminal deleted HSF1 (a.a. 1-290) but not with full-length HSF1 under non-stressed conditions. Interestingly, interaction of CHIP with full-length HSF1 was induced by heat shock treatment. The structural change of HSF1 was observed under heat stressed conditions by CD spectra. These observations demonstrate the direct interaction between HSF1 and CHIP and this interaction requires conformational change of HSF1 by heat stress.     

At least two Toc34 protein import receptors with different specificities are also present in spinach chloroplasts

The receptor components of the chloroplast protein import machinery, Toc34 and Toc159, are both encoded by small gene families in Arabidopsis thaliana. Recent results suggest that each member of these families preferentially interacts with different groups of precursor proteins. Here we address the question, whether multiple homologous Toc receptors are unique to Arabidopsis or whether they are a general phenomenon in plants. Indeed, in spinach we could identify at least two Toc34 proteins with different substrate specificities as demonstrated by competition and antibody inhibition experiments. In addition, an analysis of the available genomic data revealed the presence of at least two Toc34 homologs in six other plant species.     

African ancestry of the population of Buenos Aires

The population of Argentina today does not have a “visible” black African component. However, censuses conducted during most of the 19th century registered up to 30% of individuals of African origin living in Buenos Aires city. What has happened to this African influence? Have all individuals of African origin died, as lay people believe? Or is it possible that admixture with the European immigrants made the African influence “invisible?” We investigated the African contribution to the genetic pool of the population of Buenos Aires, Argentina, typing 12 unlinked autosomal DNA markers in a sample of 90 individuals. The results of this analysis suggest that 2.2% (SEM = 0.9%) of the genetic ancestry of the Buenos Aires population is derived from Africa. Our analysis of individual admixture shows that those alleles that have a high frequency in populations of African origin tend to concentrate among 8 individuals in our sample. Therefore, although the admixture estimate is relatively low, the actual proportion of individuals with at least some African influence is approximately 10%. The evidence we are presenting of African ancestry is consistent with the known historical events that led to the drastic reduction of the Afro‐Argentine population during the second half of the 19th century. However, as our results suggest, this reduction did not mean a total disappearance of African genes from the genetic pool of the Buenos Aires population. Am J Phys Anthropol 128:164‐170, 2005. © 2005 Wiley‐Liss, Inc.     

Diuretic factors and second messengers stimulate secretion of the organic cation TEA by the Malpighian tubules of Drosophila melanogaster

This study showed that four factors which stimulate transepithelial fluid secretion and inorganic ion transport across the main segment of the Malpighian tubules of Drosophila melanogaster also stimulate transepithelial secretion of the prototypical organic cation tetraethylammonium (TEA). TEA fluxes across the Malpighian tubules and gut were measured using a TEA-selective self-referencing (TEA-SeR) microelectrode. TEA flux across isolated Malpighian tubules was also measured using a TEA-selective microelectrode positioned in droplets of fluid secreted by tubules set up in a modified Ramsay assay. TEA flux was stimulated by the intracellular second messengers cAMP and cGMP, which increase the lumen-positive transepithelial potential (TEP), and also by tyramine and leucokinin-I (LK-I), which decrease TEP. The largest increase was measured in response to 1 micromol l-1 LK-I which increased transepithelial TEA flux by 72%. TEA flux in the lower tubule was stimulated slightly (13%) by 1 micromol l-1 tyramine but not by any of the other factors. TEA flux across the midgut was unaffected by cAMP, cGMP or tyramine. This is the first study to demonstrate the effects of insect diuretic factors and second messengers on excretion of organic cations.