Stereochemical control over Mn(II)-thio versus Mn(II)-oxy coordination in adenosine 5'-O-(1-thiodiphosphate) complexes at the active site of creatine kinase

The stereochemical configurations of the Mn(II) complexes with the resolved epimers of adenosine 5'-O-(1-thiodiphosphate) (ADP alpha S), bound at the active site of creatine kinase, have been determined in order to assess the relative strengths of enzymic stereoselectivity versus Lewis acid/base preferences in metal-ligand binding. Electron paramagnetic resonance (EPR) data have been obtained for Mn(II) in anion-stabilized, dead-end (transition-state analogue) complexes, in ternary enzyme-MnIIADP alpha S complexes, and in the central complexes of the equilibrium mixture. The modes of coordination of Mn(II) at P alpha in the nitrate-stabilized, dead-end complexes with each epimer of ADP alpha S were ascertained by EPR measurements with (Rp)-[alpha-17O]ADP alpha S and (Sp)-[alpha-17O]ADP alpha S. The EPR spectrum for the complex with (Rp)-[alpha-17O]ADP alpha S showed inhomogeneous broadening due to unresolved superhyperfine coupling from coordinated 17O at P alpha. By contrast, the EPR spectrum for Mn(II) in complex with (Sp)-[alpha-17O]ADP alpha S is indistinguishable from that obtained for a matched sample with unlabeled (Sp)-ADP alpha S. A reduction in the magnitude of the 55Mn hyperfine coupling constant in the spectrum for the complex containing (Sp)-ADP alpha S is indicative of Mn(II)-thio coordination at P alpha.(ABSTRACT TRUNCATED AT 250 WORDS)     

Observation of manganese(II)-ligand superhyperfine couplings in complexes with proteins by electron spin-echo spectroscopy

Pulsed electron paramagnetic resonance spectroscopy has been used to detect Mn(II)-ligand superhyperfine couplings in complexes with creatine kinase and in the Mn(II) metalloprotein concanavalin A. Electron spin-echo envelopes from Mn(II), bound in these complexes, are modulated by superhyperfine interactions between Mn(II) and nearby, weakly coupled nuclear spins. The characteristic frequencies of the modulations were obtained by Fourier transformation of the three-pulse, spin-echo envelopes. In transition-state analogue complexes of creatine kinase (enzyme-MnIIADP-anion-creatine), superhyperfine interactions from the directly coordinated nitrogen of the thiocyanate ligand give envelope modulations. The source of the modulations was confirmed by measurements with the 14N and 15N forms of thiocyanate. On the other hand, the nitrogen of coordinated nitrate, which is two bonds removed from the paramagnetic center, does not produce detectable modulations. In spectra for Mn(II) concanavalin A, envelope modulations are detected due to the nitrogen of the coordinated histidine residue. Complexes prepared in 2H2O give strong signals due to weakly coupled 2H. For Mn(II)-doped single crystals of sodium pyrophosphate, signals are observed in the frequency domain spectra that are due to coupling from 31P. Phosphorus signals from the ADP ligand in complexes with creatine kinase show approximately the same coupling constant but have a much broader line width.     

Schistosoma mansoni: complexity of antigenic and nonantigenic surface polypeptides

Two-dimensional gel analysis of the surface polypeptides of the schistosomula stage of Schistosoma mansoni resolved a complex pattern of approximately 20 polypeptides. The majority of these were identified as immunogenic since they were immunoprecipitated with antisera from chronically infected mice and from mice vaccinated with irradiated cercariae. However, several major surface polypeptides were not immunoprecipitated by sera from infected or immune mice and were presumed to be nonantigenic.     

31P nuclear magnetic resonance study of phosphoribosyldiphosphate and its interaction with magnesium ions

31P NMR has been used to study phosphoribosyldiphosphate (P-Rib-PP) over a wide range of pH values, both in the absence and presence of MgCl2. In the absence of MgCl2, the chemical shift variations of the three 31P nuclei in the molecule, over the pH range 4 to 9, were found to be largest for the terminal 1-diphosphate (1P beta) oxyanion and the 5-phosphate (5P) moiety. Apparent pK alpha values of approximately 6.1 and 6.3 were estimated for protonation of the 1P beta and 5P groups, respectively. Variations in the apparent pK alpha values associated with 1P beta and 5P oxyanions in the presence of various concentrations of MgCl2 were consistent with P-Rib-PP having two independent metal ion binding sites with different affinities for Mg2+ ions. The binding of Mg2+ reduced the apparent pK alpha of the 1P beta moiety by approximately 1.6 units and the apparent pK alpha of the 5P group by approximately 0.7 unit. This behavior is analogous to the situation reported for the terminal phosphooxyanion of ADP and observed for the phosphate group of ribose 5-phosphate, respectively. In the presence of an equimolar concentration of added MgCl2, the 1P alpha and 1P beta resonances of P-Rib-PP were shifted downfield and the 31P-31P coupling constant was decreased. Changes in both these parameters were very similar to those reported for the MgADP- complex. The observed chemical shifts and spin-spin coupling constants suggest that the diphosphate and monophosphate moieties of P-Rib-PP act as independent binding sites for Mg2+ in a manner similar to the phosphooxyanion groups of ADP and ribose 5-phosphate, respectively.     

Parenting Practices at 24 to 47 Months and IQ at Age 8: Effect-Measure Modification by Infant Temperament

Cognitive development might be influenced by parenting practices and child temperament. We examined whether the associations between parental warmth, control and intelligence quotient (IQ) may be heightened among children in difficult temperament. Participants were from the Avon Longitudinal Study of Parents and Children (n = 7,044). Temperament at 6 months was measured using the Revised Infant Temperament Questionnaire and classified into ‘easy’ and ‘difficult’. Parental warmth and control was measured at 24 to 47 months and both were classified into 2 groups using latent class analyses. IQ was measured at 8 years using the Wechsler Intelligence Scale for Children and dichotomized (<85 and ≥85) for analyzing effect-measure modification by temperament. Linear regression adjusted for multiple confounders and temperament showed lower parental warmth was weakly associated with lower IQ score [β = -0.52 (95% CI 1.26, 0.21)], and higher parental control was associated with lower IQ score [β = -2.21 (-2.95, -1.48)]. Stratification by temperament showed no increased risk of having low IQ in temperamentally difficult children [risk ratio (RR) = 0.97 95% CI 0.65, 1.45)] but an increased risk among temperamentally easy children (RR = 1.12 95% CI 0.95, 1.32) when parental warmth was low. There was also no increased risk of having low IQ in temperamentally difficult children (RR = 1.02 95% CI 0.69, 1.53) but there was an increased risk among temperamentally easy children (RR = 1.30 95% CI 1.11, 1.53) when parental control was high. For both parental warmth and control, there was some evidence of negative effect-measure modification by temperament on the risk-difference scale and the risk-ratio scale. It may be more appropriate to provide parenting interventions as a universal program rather than targeting children with difficult temperament.     

Xhex-expressing endodermal tissues are essential for anterior patterning in Xenopus

Two regions expressing Hex in the early gastrula contribute to organizing the anterior of the vertebrate embryo. In Xenopus, these include the anterior yolky endoderm and the suprablastoporal endoderm (SBE), which is fated to form the epithelial lining of the gut. These tissues may correspond to the anterior visceral endoderm and anterior definitive endoderm of amniotes. Genetic studies in mice have demonstrated the important roles of these tissues in producing anterior identity in the adjacent neural ectoderm. In Xenopus, both the anterior endoderm and the SBE have anterior inducing properties; furthermore, the SBE can organize a full anterior-posterior axis. Inhibition of Xhex function shows that both these Xhex-expressing endodermal tissues are required for anterior development in Xenopus.     

Mitogenic whey extract stimulates wound repair activity in vitro and promotes healing of rat incisional wounds

The ability of single growth factors to promote healing of normal and compromised wounds has been well described, but wound healing is a process requiring the coordinated action of multiple growth factors. Only the synergistic effect on wound healing of combinations containing at most two individual growth factors has been reported. We sought to assess the ability of a novel milk-derived growth factor-enriched preparation ?mitogenic bovine whey extract (MBWE), which contains six known growth factors, to promote repair processes in organotypic in vitro models and incisional wounds in vivo. MBWE stimulated the contraction of fibroblast-populated collagen lattices in a dose-dependent fashion and promoted the closure of excisional wounds in embryonic day 17 fetal rat skin. Application of MBWE increased incisional wound strength in normal animals on days 3, 5, 7, and 10 and reversed the decrease in wound strength observed following steroid treatment. Wound histology showed increased fibroblast numbers in wounds from normal and steroid-compromised animals. These data suggest the mixture of factors present in bovine milk exerts a direct action on the cells of cutaneous wound repair to enhance both normal and compromised healing.     

Multiple binding sites for fatty acids on the potassium channel KcsA

Interactions of fatty acids with the potassium channel KcsA were studied using Trp fluorescence quenching and electron paramagnetic resonance (EPR) techniques. The brominated analogue of oleic acid was shown to bind to annular sites on KcsA and to the nonannular sites at each protein-protein interface in the homotetrameric structure with binding constants relative to dioleoylphosphatidylcholine of 0.67 ± 0.04 and 0.87 ± 0.08, respectively. Mutation of the two Arg residues close to the nonannular binding sites had no effect on fatty acid binding. EPR studies with a spin-labeled analogue of stearic acid detected a high-affinity binding site for the fatty acid with strong immobilization. Fluorescence quenching studies with the spin-labeled analogue showed that the binding site detected in the EPR experiments could not be one of the annular or nonannular binding sites. Instead, it is proposed that the EPR studies detect binding to the central hydrophobic cavity of the channel, with a binding constant in the range of ~0.1-1 μM.