Plasmodium Para-Aminobenzoate Synthesis and Salvage Resolve Avoidance of Folate Competition and Adaptation to Host Diet

1. Download high-res image (150KB)
2. Download full-size image

     

Relation of B-type natriuretic peptide to left ventricular wall stress as assessed by cardiac magnetic resonance imaging in patients with dilated cardiomyopathy

Ventricular loading conditions are crucial determinants of cardiac function and prognosis in heart failure. B-type natriuretic peptide (BNP) is mainly stored in the ventricular myocardium and is released in response to an increased ventricular filling pressure. We examined, therefore, the hypothesis that BNP serum concentrations are related to ventricular wall stress. Cardiac magnetic resonance imaging (MRI) was used to assess left ventricular (LV) mass and cardiac function of 29 patients with dilated cardiomyopathy and 5 controls. Left ventricular wall stress was calculated by using a thick-walled sphere model, and BNP was assessed by immunoassay. LV mass (r = 0.73, p < 0.001) and both LV end-diastolic (r = 0.54, p = 0.001) and end-systolic wall stress (r = 0.66, p < 0.001) were positively correlated with end-diastolic volume. LV end-systolic wall stress was negatively related to LV ejection fraction (EF), whereas end-diastolic wall stress was not related to LVEF. BNP concentration correlated positively with LV end-diastolic wall stress (r = 0.50, p = 0.002). Analysis of variance revealed LV end-diastolic wall stress as the only independent hemodynamic parameter influencing BNP (p < 0.001). The present approach using a thick-walled sphere model permits determination of mechanical wall stress in a clinical routine setting using standard cardiac MRI protocols. A correlation of BNP concentration with calculated LV stress was observed in vivo. Measurement of BNP seems to be sufficient to assess cardiac loading conditions. Other relations of BNP with various hemodynamic parameters (e.g., EF) appear to be secondary. Since an increased wall stress is associated with cardiac dilatation, early diagnosis and treatment could potentially prevent worsening of the outcome.     

Mutant analyses reveal different functions of fgfr1 in medaka and zebrafish despite conserved ligand-receptor relationships

Medaka (Oryzias latipes) is a small freshwater teleost that provides an excellent developmental genetic model complementary to zebrafish. Our recent mutagenesis screening using medaka identified headfish (hdf) which is characterized by the absence of trunk and tail structures with nearly normal head including the midbrain-hindbrain boundary (MHB). Positional-candidate cloning revealed that the hdf mutation causes a functionally null form of Fgfr1. The fgfr1hdf is thus the first fgf receptor mutant in fish. Although FGF signaling has been implicated in mesoderm induction, mesoderm is induced normally in the fgfr1hdf mutant, but subsequently, mutant embryos fail to maintain the mesoderm, leading to defects in mesoderm derivatives, especially in trunk and tail. Furthermore, we found that morpholino knockdown of medaka fgf8 resulted in a phenotype identical to the fgfr1hdf mutant, suggesting that like its mouse counterpart, Fgf8 is a major ligand for Fgfr1 in medaka early embryogenesis. Intriguingly, Fgf8 and Fgfr1 in zebrafish are also suggested to form a major ligand-receptor pair, but their function is much diverged, as the zebrafish fgfr1 morphant and zebrafish fgf8 mutant acerebellar (ace) only fail to develop the MHB, but develop nearly unaffected trunk and tail. These results provide evidence that teleost fish have evolved divergent functions of Fgf8-Fgfr1 while maintaining the ligand-receptor relationships. Comparative analysis using different fish is thus invaluable for shedding light on evolutionary diversification of gene function.     

Adaptation of a quantitative trait to a moving optimum

We investigate adaptive evolution of a quantitative trait under stabilizing selection with a moving optimum. We characterize three regimes, depending on whether (1) the beneficial mutation rate, (2) the fixation time, or (3) the rate of environmental change is the limiting factor for adaptation. If the environment is rate limiting, mutations with a small phenotypic effect are preferred over large mutations, in contrast to standard theory.     

Biophysics and bioinformatics reveal structural differences of the two peripheral stalk subunits in chloroplast ATP synthase

ATP synthases convert an electrochemical proton gradient into rotational movement to produce the ubiquitous energy currency adenosine triphosphate. Tension generated by the rotational torque is compensated by the stator. For this task, a peripheral stalk flexibly fixes the hydrophilic catalytic part F1 to the membrane integral proton conducting part F(O) of the ATP synthase. While in eubacteria a homodimer of b subunits forms the peripheral stalk, plant chloroplasts and cyanobacteria possess a heterodimer of subunits I and II. To better understand the functional and structural consequences of this unique feature of photosynthetic ATP synthases, a procedure was developed to purify subunit I from spinach chloroplasts. The secondary structure of subunit I, which is not homologous to bacterial b subunits, was compared to heterologously expressed subunit II using CD and FTIR spectroscopy. The content of alpha-helix was determined by CD spectroscopy to 67% for subunit I and 41% for subunit II. In addition, bioinformatics was applied to predict the secondary structure of the two subunits and the location of the putative coiled-coil dimerization regions. Three helical domains were predicted for subunit I and only two uninterrupted domains for the shorter subunit II. The predicted length of coiled-coil regions varied between different species and between subunits I and II.     

Scaffolding as an organizing principle in trans-translation. The roles of small protein B and ribosomal protein S1

A eubacterial ribosome stalled on a defective mRNA can be released through a quality control mechanism referred to as trans-translation, which depends on the coordinating binding actions of transfer-messenger RNA, small protein B, and ribosome protein S1. By means of cryo-electron microscopy, we obtained a map of the complex composed of a stalled ribosome and small protein B, which appears near the decoding center. This result suggests that, when lacking a codon, the A-site on the small subunit is a target for small protein B. To investigate the role of S1 played in trans-translation, we obtained a cryo-electron microscopic map, including a stalled ribosome, transfer-messenger RNA, and small protein Bs but in the absence of S1. In this complex, several connections between the 30 S subunit and transfer-messenger RNA that appear in the +S1 complex are no longer found. We propose the unifying concept of scaffolding for the roles of small protein B and S1 in binding of transfer-messenger RNA to the ribosome during trans-translation, and we infer a pathway of sequential binding events in the initial phase of trans-translation.     

Heterologous expression of the glutamine transporter SNAT3 in Xenopus oocytes is associated with four modes of uncoupled transport

The glutamine transporter SNAT3 (SLC38A3, former SN1) plays a major role in glutamine release from brain astrocytes and in glutamine uptake into hepatocytes and kidney epithelial cells. Here we expressed rat SNAT3 in oocytes of Xenopus laevis and reinvestigated its transport modes using two-electrode voltage clamp and pH-sensitive microelectrodes. In addition to the established coupled Na+-glutamine-cotransport/H+ antiport, we found that there are three conductances associated with SNAT3, two dependent and one independent of the amino acid substrate. The glutamine-dependent conductance is carried by cations at pH 7.4, whereas at pH 8.4 the inward currents are still dependent on the presence of external Na+ but are carried by H+. Mutation of threonine 380 to alanine abolishes the cation conductance but leaves the proton conductance intact. Under Na+-free conditions, where the substrate-dependent conductance is suppressed, a substrate-independent, outwardly rectifying current becomes apparent at pH 8.4 that is carried by K+ and H+. In addition, we identified a glutamine-dependent uncoupled Na+/H+ exchange activity that becomes apparent upon removal of Na+ in the presence of glutamine. In conclusion, our results suggest that, in addition to coupled transport, SNAT3 mediates four modes of uncoupled ion movement across the membrane.