Structure-activity relations of the molluscan neuropeptide FMRFamide on some molluscan muscles

Analogs of the molluscan neuropeptide FMRFamide were tested on four different molluscan muscle preparations which show qualitatively different responses to the peptide; the structure-activity relations are basically similar, but not identical. The C-terminal amide and the Arg³ residue are critical for FMRFamide-like activity on all four preparations. In contrast, analogs extended at the N-terminal or with conservative substitutions for the Phe¹ or Met² residue are approximately equipotent to FMRFamide. These structural requirements parallel those for the C-terminal tetrapeptide amide of gastrin.     

SNPing variation from genomes

Genomic technologies are revealing several mechanisms of insecticide resistance involving enhanced detoxification or reduced target-site sensitivity that had previously defied molecular analyses. Genome projects are also revealing some potentially far-reaching consequences for pest-insect genomes of the rapid accumulation of multiple resistance mutations in very short periods of evolutionary time.     

‘Mild mitochondrial uncoupling’ induced protection against neuronal excitotoxicity requires AMPK activity

The preconditioning response conferred by a mild uncoupling of the mitochondrial membrane potential (Δψ_m) has been attributed to altered reactive oxygen species (ROS) production and mitochondrial Ca^2 + uptake within the cells. Here we have explored if altered cellular energetics in response to a mild mitochondrial uncoupling stimulus may also contribute to the protection. The addition of 100 nM FCCP for 30 min to cerebellar granule neurons (CGNs) induced a transient depolarization of the Δψ_m, that was sufficient to significantly reduce CGN vulnerability to the excitotoxic stimulus, glutamate. On investigation, the mild mitochondrial ‘uncoupling’ stimulus resulted in a significant increase in the plasma membrane levels of the glucose transporter isoform 3, with a hyperpolarisation of Δψ_m and increased cellular ATP levels also evident following the washout of FCCP. Furthermore, the phosphorylation state of AMP-activated protein kinase (AMPK) (Thr 172) was increased within 5 min of the uncoupling stimulus and elevated up to 1 h after washout. Significantly, the physiological changes and protection evident after the mild uncoupling stimulus were lost in CGNs when AMPK activity was inhibited. This study identifies an additional mechanism through which protection is mediated upon mild mitochondrial uncoupling: it implicates increased AMPK signalling and an adaptive shift in energy metabolism as mediators of the preconditioning response associated with FCCP-induced mild mitochondrial uncoupling.     

Dual Cyclin-Binding Domains Are Required for p107 To Function as a Kinase Inhibitor

The retinoblastoma (pRB) family of proteins includes three proteins known to suppress growth of mammalian cells. Previously we had found that growth suppression by two of these proteins, p107 and p130, could result from the inhibition of associated cyclin-dependent kinases (cdks). One important unresolved issue, however, is the mechanism through which inhibition occurs. Here we present in vivo and in vitro evidence to suggest that p107 is a bona fide inhibitor of both cyclin A-cdk2 and cyclin E-cdk2 that exhibits an inhibitory constant (K_i) comparable to that of the cdk inhibitor p21/WAF1. In contrast, pRB is unable to inhibit cdks. Further reminiscent of p21, a second cyclin-binding site was mapped to the amino-terminal portions of p107 and p130. This amino-terminal domain is capable of inhibiting cyclin-cdk2 complexes, although it is not a potent substrate for these kinases. In contrast, a carboxy-terminal fragment of p107 that contains the previously identified cyclin-binding domain serves as an excellent kinase substrate although it is unable to inhibit either kinase. Clustered point mutations suggest that the amino-terminal domain is functionally important for cyclin binding and growth suppression. Moreover, peptides spanning the cyclin-binding region are capable of interfering with p107 binding to cyclin-cdk2 complexes and kinase inhibition. Our ability to distinguish between p107 and p130 as inhibitors rather than simple substrates suggests that these proteins may represent true inhibitors of cdks.     

About the specificity of photoinduced affinity labeling of Escherichia coli ribosomes by dihydrorosaramicin, a macrolide related to erythromycin

Photoactivation of the [3H]dihydrorosaramicin chromophore at a wavelength above 300 nm allows the covalent attachment of the macrolide antibiotic to the bacterial ribosome. Bidimensional electrophoresis shows that the radioactivity is mainly associated with proteins L1, L5, L6, L15, L18, L19, S1, S3, S4, S5 and S9. When photoincorporation of the drug is conducted in the presence of puromycin as effector of [3H]dihydrorosaramicin-binding sites, a decrease in the labeling of most proteins is observed, except for L18 and L19, which are radiolabeled to a larger extent. These results allow us to speculate that L18 and L19 belong to the high-affinity binding site of rosaramicin antibiotic.     

Purification of human plasma fibronectin by double affinity chromatography on gelatin and heparin-Trisacryl

In this work the human plasma fibronectin was purified by affinity chromatography using a tandem column system. The first affinity column was filled with gelatin-Trisacryl whereas the second one contained heparin-Trisacryl. This double affinity chromatography demonstrated its high efficiency in term of purity and yield. Several analytical methods (electrophoresis, immunoelectrophoresis, F.P.L.C. and adhesion assay on cultured eucaryotic cells) evidenced in fact the high purity of the preparation as well as its biological behaviour in term of cell adhesion and spreading. The performances of the sorbents used facilitate the scaling up when large quantities of FNP are needed.