Heavy metal stress. Activation of distinct mitogen-activated protein kinase pathways by copper and cadmium

Excessive amounts of heavy metals adversely affect plant growth and development. Whereas some regions naturally contain high levels of heavy metals, anthropogenic release of heavy metals into the environment continuously increases soil contamination. The presence of elevated levels of heavy metal ions triggers a wide range of cellular responses including changes in gene expression and synthesis of metal-detoxifying peptides. To elucidate signal transduction events leading to the cellular response to heavy metal stress we analyzed protein phosphorylation induced by elevated levels of copper and cadmium ions as examples for heavy metals with different physiochemical properties and functions. Exposure of alfalfa (Medicago sativa) seedlings to excess copper or cadmium ions activated four distinct mitogen-activated protein kinases (MAPKs): SIMK, MMK2, MMK3, and SAMK. Comparison of the kinetics of MAPK activation revealed that SIMK, MMK2, MMK3, and SAMK are very rapidly activated by copper ions, while cadmium ions induced delayed MAPK activation. In protoplasts, the MAPK kinase SIMKK specifically mediated activation of SIMK and SAMK but not of MMK2 and MMK3. Moreover, SIMKK only conveyed MAPK activation by CuCl(2) but not by CdCl(2). These results suggest that plants respond to heavy metal stress by induction of several distinct MAPK pathways and that excess amounts of copper and cadmium ions induce different cellular signaling mechanisms in roots.     

Crystal structure of human factor VIIa/tissue factor in complex with peptide mimetic inhibitor

The 3D structure of human factor VIIa/soluble tissue factor in complex with a peptide mimetic inhibitor, propylsulfonamide-D-Thr-Met-p-aminobenzamidine, is determined by X-ray crystallography. As compared with the interactions between thrombin and thrombin inhibitors, the interactions at S2 and S3 sites characteristic of factor VIIa and factor VIIa inhibitors are revealed. The S2 site has a small pocket, which is filled by the hydrophobic methionine side chain in P2. The small S3 site fits the small size residue, D-threonine in P3. The structural data and SAR data of the peptide mimetic inhibitor show that these interactions in the S2 and S3 sites play an important role for the improvement of selectivity versus thrombin. The results will provide valuable information for the structure-based drug design of specific inhibitors for FVIIa/TF.     

Evaluation of bifidobacterial adhesion to acidic sugar chains of porcine colonic mucins

The aim of this study was to assess the adhesion of Bifidobacterium strains to acidic carbohydrate moieties of porcine colonic mucin. Mucins were extracted and purified via gel filtration chromatography followed by density-gradient ultracentrifugation. The presence of sulfated and sialylated carbohydrates in mucins was shown by enzyme-linked immunosorbent assays using PGM34 and HMC31 monoclonal antibodies (mAbs), respectively. Adhesion of Bifidobacterium strains to mucin preparations was markedly affected by the degree of purification. In eight of 22 strains, we observed increased adhesion to mucin preparations purified by ultracentrifugation. Moreover, in some of these eight strains, adhesion to mucin was reduced by pretreatment with sulfatase and/or sialidase, and competitively inhibited by pretreatment with PGM34 and/or HCM31 mAbs. Our results showed that some Bifidobacterium strains adhered to sulfo- and/or sialomucin and were able to recognize carbohydrate structures of the mAbs epitopes.     

Role of alpha-tocopherol in the regulation of mitochondrial permeability transition

We previously showed that Ca2+-induced cyclosporin A-sensitive membrane permeability transition (MPT) of mitochondria occurred with concomitant generation of reactive oxygen species (ROS) and release of cytochrome c (Free Rad. Res.38, 29-35, 2004). To elucidate the role of alpha-tocopherol in MPT, we investigated the effect of alpha-tocopherol on mitochondrial ROS generation, swelling and cytochrome c release induced by Ca2+ or hydroxyl radicals. Biochemical analysis revealed that alpha-tocopherol suppressed Ca2+-induced ROS generation and oxidation of critical thiol groups of mitochondrial adenine nucleotide translocase (ANT) but not swelling and cytochrome c release. Hydroxyl radicals also induced cyclosporin A-sensitive MPT of mitochondria. alpha-Tocopherol suppressed the hydroxyl radical-induced lipid peroxidation, swelling and cytochrome c release from mitochondria. These results indicate that alpha-tocopherol inhibits ROS generation, ANT oxidation, lipid peroxidation and the opening of MPT, thereby playing important roles in the prevention of oxidative cell death.