The N-terminal domain of annexin 2 serves as a secondary binding site during membrane bridging

Annexin A2 (AnxA2) is a Ca(2+)- and acidic phospholipid-binding protein involved in many cellular processes. It undergoes Ca(2+)-mediated membrane bridging at neutral pH and has been demonstrated to be involved in an H(+)-mediated mechanism leading to a novel AnxA2-membrane complex structure. We used fluorescence techniques to characterize this H(+)-dependent mechanism at the molecular level; in particular, the involvement of the AnxA2 N-terminal domain. This domain was labeled at Cys-8 either with acrylodan or pyrene-maleimide fluorescent probes. Steady-state and time-resolved fluorescence analysis for acrylodan and fluorescence quenching by doxyl-labeled phospholipids revealed direct interaction between the N-terminal domain and the membrane. The absence of pyrene excimer suggested that interactions between N termini are not involved in the H(+)-mediated mechanism. These findings differ from those previously observed for the Ca(2+)-mediated mechanism. Protein titration experiments showed that the protein concentration for half-maximal membrane aggregation was twice for Ca(2+)-mediated compared with H(+)-mediated aggregation, suggesting that AnxA2 was able to bridge membranes either as a dimer or as a monomer, respectively. An N-terminally deleted AnxA2 was 2-3 times less efficient than the wild-type protein for H(+)-mediated membrane aggregation. We propose a model of AnxA2-membrane assemblies, highlighting the different roles of the N-terminal domain in the H(+)- and Ca(2+)-mediated membrane bridging mechanisms.     

Salicyl alcohol oxidase of the chemical defense secretion of two chrysomelid leaf beetles. Molecular and functional characterization of two new members of the glucose-methanol-choline oxidoreductase gene family

Salicyl alcohol oxidase is an extracellular enzyme that occurs in glandular reservoirs of chrysomelid leaf beetle larvae and catalyzes the formation of salicylaldehyde, a volatile deterrent used by the larvae against predators. Salicyl alcohol is the hydrolysis product of salicin, a plant-derived precursor taken up by the beetle larvae from the leaves of willow and poplar trees. The cDNA encoding salicyl alcohol oxidase from two related species Chrysomela tremulae and Chrysomela populi has been identified, cloned, and expressed in an active form in Escherichia coli. The open reading frame of 623 amino acids begins in both enzymes with an N-terminal signal peptide of 21 amino acids. Sequence comparison has revealed that salicyl alcohol oxidase belongs to the family of glucose-methanol-choline oxidoreductase-like sequences with mostly unknown function. Enzymes of this family share similar overall structure with an essentially identical FAD-binding site but possess different catalytic activities. The data suggest that salicyl alcohol oxidase, essential for the activation of the plant-derived precursor salicin, was originally recruited from an oxidase involved in the autogenous biosynthesis of iridoid monoterpenes and found in related chrysomelid leaf beetle species.     

Characterization of truncated forms of abnormal prion protein in Creutzfeldt-Jakob disease

In prion disease, the abnormal conformer of the cellular prion protein, PrP(Sc), deposits in fibrillar protein aggregates in brain and other organs. Limited exposure of PrP(Sc) to proteolytic digestion in vitro generates a core fragment of 19-21 kDa, named PrP27-30, which is also found in vivo. Recent evidence indicates that abnormal truncated fragments other than PrP27-30 may form in prion disease either in vivo or in vitro. We characterized a novel protease-resistant PrP fragment migrating 2-3 kDa faster than PrP27-30 in Creutzfeldt-Jakob disease (CJD) brains. The fragment has a size of about 18.5 kDa when associated with PrP27-30 type 1 (21 kDa) and of 17 kDa when associated with type 2 (19 kDa). Molecular mass and epitope mapping showed that the two fragments share the primary N-terminal sequence with PrP27-30 types 1 and 2, respectively, but lack a few amino acids at the very end of C terminus together with the glycosylphosphatidylinositol anchor. The amounts of the 18.5- or 17-kDa fragments and the previously described 13-kDa PrP(Sc) C-terminal fragment relatively to the PrP27-30 signal significantly differed among CJD subtypes. Furthermore, protease digestion of PrP(Sc) or PrP27-30 in partially denaturing conditions generated an additional truncated fragment of about 16 kDa only in typical sporadic CJD (i.e. MM1). These results show that the physicochemical heterogeneity of PrP(Sc) in CJD extends to abnormal truncated forms of the protein. The findings support the notion of distinct structural "conformers" of PrP(Sc) and indicate that the characterization of truncated PrP(Sc) forms may further improve molecular typing in CJD.     

Low dose beta-blocker prevents ovariectomy-induced bone loss in rats without affecting heart functions

Findings from animal studies have suggested that bone remodeling is under beta-adrenergic control. However, the level of adrenergic inhibition required to achieve the most favorable effects on the skeleton remains unknown. To address this question, we compared the effects of low (0.1 mg/Kg/day), medium (5 mg/Kg/day) or high (20 mg/Kg/day) doses of propranolol given 5 days per week for 10 weeks in ovariectomized (OVX) rats. Characteristics of bone microarchitecture, biomechanical properties and bone turnover were investigated, whilst heart functions were assessed by echocardiography and catheterization of the left ventricle. We first confirmed the expression of Adrbeta2R and the absence of Adrbeta1R on osteoblasts by PCR and confocal microscopy. We then showed that low dose propranolol prevented OVX induced bone loss by increasing bone formation (+30% of MAR vs. placebo, P = 0.01) and decreasing bone resorption (-52% of osteoclast surface on bone surface vs. placebo, P = 0.01). Consequently, rats receiving 0.1 mg/kg/day propranolol displayed higher stress (+27%), intrinsic energy (+28.7%) and Young's Modulus in compression versus placebo (all, P < 0.05). No significant effects on heart hemodynamic parameters were found in rats receiving this dose. In contrast, medium and high doses of propranolol had a negative effect on heart functions but no significant protective effects on bone mass in ovariectomized rats. These results, consistent with the dominant nature of the high bone mass phenotype and normal heart function of Adrbeta2R-deficient mice, suggest that low doses of beta-blockers may have a therapeutic utility in the treatment of osteoporosis with high selectivity for bone tissues.     

Periostin, a member of a novel family of vitamin K-dependent proteins, is expressed by mesenchymal stromal cells

The modification of glutamic acid residues to gamma-carboxyglutamic acid (Gla) is a post-translational modification catalyzed by the vitamin K-dependent enzyme gamma-glutamylcarboxylase. Despite ubiquitous expression of the gamma-carboxylation machinery in mammalian tissues, only 12 Gla-containing proteins have so far been identified in humans. Because bone tissue is the second most abundant source of Gla-containing proteins after the liver, we sought to identify Gla proteins secreted by bone marrow-derived mesenchymal stromal cells (MSCs). We used a proteomics approach to screen the secretome of MSCs with a combination of two-dimensional gel electrophoresis and tandem mass spectrometry. The most abundant Gla-containing protein secreted by MSCs was identified as periostin, a previously unrecognized gamma-carboxylated protein. In silico amino acid sequence analysis of periostin demonstrated the presence of four consensus gamma-carboxylase recognition sites embedded within fasciclin-like protein domains. The carboxylation of periostin was confirmed by immunoprecipitation and purification of the recombinant protein. Carboxylation of periostin could be inhibited by warfarin in MSCs, demonstrating its dependence on the presence of vitamin K. We were able to demonstrate localization of carboxylated periostin to bone nodules formed by MSCs in vitro, suggesting a role in extracellular matrix mineralization. Our data also show that another fasciclin I-like protein, betaig-h3, contains Gla. In conclusion, periostin is a member of a novel vitamin K-dependent gamma-carboxylated protein family characterized by the presence of fasciclin domains. Furthermore, carboxylated periostin is produced by bone-derived cells of mesenchymal lineage and is abundantly found in mineralized bone nodules in vitro.     

Self-association of adenine-dependent hairpin ribozymes

Hairpin ribozymes are flexible molecules that catalyse reversible self-cleavage after the docking of two independently folded internal loops, A and B. The activities, self-association and structures in solution of two 85 base adenine-dependent hairpin ribozymes (ADHR1 and ADHR2) were studied by native gel electrophoresis, analytical centrifugation, and small angle neutron scattering. Bi-molecular RNA interactions such as linear–linear, loop–loop, loop–linear or kissing interactions have been found to be important in the control of various biological functions, and hairpin loops present rich potential for establishing both intra- and intermolecular interactions through standard Watson-Crick base pairing or non-canonical interactions. Similar results were obtained for ADHR1 and ADHR2. At room temperature, they indicated end-to-end self-association of the ribozymes in rod-like structures with a cross-section corresponding to two double strands side-by-side. Dimers, which predominate at low concentration (∼0.1 mg/ml), associate into longer rods, with increasing concentration (∼1 mg/ml). Above 65°C, the dimers and rods dissociated into compact monomers, with a radius of gyration similar to that of tRNA (about 70 bases). The dimers were non-active for catalysis, which suggests that dimer formation, probably by preventing the correct docking of loops A and B, could act as an inhibition mechanism for the regulation of hairpin ribozyme catalysis.     

The relationships between Ixodes ricinus and small mammal species at the woodland–pasture interface

Ixodes ricinus, as vector, and small mammals, as reservoirs, are implicated in pathogen transmission between wild fauna, domestic animals and humans at the woodland–pasture interface. The ecological relationship between ticks and small mammals was monitored in 2005 on four bocage (enclosed pastureland) sites in central France, where questing ticks were collected by dragging and small mammals were trapped. Questing I. ricinus tick and small mammal locations in the environment were assessed through correspondence analysis. I. ricinus larval burden on small mammals was modeled using a negative binomial law. The correspondence analyses underlined three landscape features: grassland, hedgerow, and woodland. Seven small mammal species were trapped, while questing ticks were all I. ricinus, with the highest abundance in woodland and the lowest in pasture. The small mammals were overall more abundant in hedgerow, less present in woodland and sparse in grassland. They carried mainly I. ricinus, and secondarily I. acuminatus and I. trianguliceps. The most likely profile for a tick-infested small mammal corresponded to a male wood mouse (Apodemus sylvaticus) in woodland or hedgerow during a dry day. A. sylvaticus, which was the only species captured in grassland, but was also present in hedgerow and woodland, may be a primary means of transfer of I. ricinus larvae from woodland to pasture.     

X-ray structure of the metal-sensor CnrX in both the apo- and copper-bound forms

Both the X-ray structures of the apo- and the copper-bound forms of the metal-sensor domain (residues 31-148) of CnrX from Cupriavidus metallidurans CH34 were obtained at 1.74 Å resolution from a selenomethionine derivative. This four-helix hooked-hairpin is the first structure of a metal-sensor in an ECF-type signaling pathway. The copper ion is bound in a type 2-like center with a 3N1O coordination in the equatorial plane and shows an unprecedented remote fifth axial ligand with Met93 contributing a weak S-Cu bond. The signal onset cannot be explained by conformational changes associated with CnrX metallation.