Accommodating variety in iron-responsive elements: Crystal structure of transferrin receptor 1 B IRE bound to iron regulatory protein 1

Iron responsive elements (IREs) are short stem-loop structures found in several mRNAs encoding proteins involved in cellular iron metabolism. Iron regulatory proteins (IRPs) control iron homeostasis through differential binding to the IREs, accommodating any sequence or structural variations that the IREs may present. Here we report the structure of IRP1 in complex with transferrin receptor 1 B (TfR B) IRE, and compare it to the complex with ferritin H (Ftn H) IRE. The two IREs are bound to IRP1 through nearly identical protein-RNA contacts, although their stem conformations are significantly different. These results support the view that binding of different IREs with IRP1 depends both on protein and RNA conformational plasticity, adapting to RNA variation while retaining conserved protein-RNA contacts.     

Molecular basis for failure of "atypical" C1 domain of Vav1 to bind diacylglycerol/phorbol ester

C1 domains, the recognition motif of the second messenger diacylglycerol and of the phorbol esters, are classified as typical (ligand-responsive) or atypical (not ligand-responsive). The C1 domain of Vav1, a guanine nucleotide exchange factor, plays a critical role in regulation of Vav activity through stabilization of the Dbl homology domain, which is responsible for exchange activity of Vav. Although the C1 domain of Vav1 is classified as atypical, it retains a binding pocket geometry homologous to that of the typical C1 domains of PKCs. This study clarifies the basis for its failure to bind ligands. Substituting Vav1-specific residues into the C1b domain of PKCδ, we identified five crucial residues (Glu(9), Glu(10), Thr(11), Thr(24), and Tyr(26)) along the rim of the binding cleft that weaken binding potency in a cumulative fashion. Reciprocally, replacing these incompatible residues in the Vav1 C1 domain with the corresponding residues from PKCδ C1b (δC1b) conferred high potency for phorbol ester binding. Computer modeling predicts that these unique residues in Vav1 increase the hydrophilicity of the rim of the binding pocket, impairing membrane association and thereby preventing formation of the ternary C1-ligand-membrane binding complex. The initial design of diacylglycerol-lactones to exploit these Vav1 unique residues showed enhanced selectivity for C1 domains incorporating these residues, suggesting a strategy for the development of ligands targeting Vav1.     

Microbial Transport, Survival, and Succession in a Sequence of Buried Sediments

Abstract Two chronosequences of unsaturated, buried loess sediments, ranging in age from <10,000 years to >1 million years, were investigated to reconstruct patterns of microbial ecological succession that have occurred since sediment burial. The relative importance of microbial transport and survival to succession was inferred from sediment ages, porewater ages, patterns of abundance (measured by direct counts, counts of culturable cells, and total phospholipid fatty acids), activities (measured by radiotracer and enzyme assays), and community composition (measured by phospholipid fatty acid patterns and Biolog substrate usage). Core samples were collected at two sites 40 km apart in the Palouse region of eastern Washington State, near the towns of Washtucna and Winona. The Washtucna site was flooded multiple times during the Pleistocene by glacial outburst floods; the Winona site elevation is above flood stage. Sediments at the Washtucna site were collected from near surface to 14.9 m depth, where the sediment age was approximately 250 ka and the porewater age was 3700 years; sample intervals at the Winona site ranged from near surface to 38 m (sediment age: approximately 1 Ma; porewater age: 1200 years). Microbial abundance and activities declined with depth at both sites; however, even the deepest, oldest sediments showed evidence of viable microorganisms. Same-age sediments had equal quantities of microorganisms, but different community types. Differences in community makeup between the two sites can be attributed to differences in groundwater recharge and paleoflooding. Estimates of the microbial community age can be constrained by porewater and sediment ages. In the shallower sediments (<9 m at Washtucna, <12 m at Winona), the microbial communities are likely similar in age to the groundwater; thus, microbial succession has been influenced by recent transport of microorganisms from the surface. In the deeper sediments, the populations may be considerably older than the porewater ages, since microbial transport is severely restricted in unsaturated sediments. This is particularly true at the Winona site, which was never flooded.     

Analysis of sister chromatid exchanges in the 1st, 2d and 3d mitoses using 5-bromodeoxyuridine and 5-bromodeoxycytidine

The cultures of Chinese hamster cells were treated with different concentrations (2.5, 5.0, 10.0, 20.0, 80.0 and 160.0 microgram/ml) 5-BrdU and 5-BrdC during 12 hours. The cultures were fixed at the 24-th hour. The linear increase of sister chromatid exchanges (SCE) was discovered with the increase of BrdU concentration. No change of SCE frequency was observed at different BrdC concentrations. The reasons for these differences in a concentration effect are discussed.     

Yeast superoxide dismutase: isolation and properties (review of the literature)]

Modern data are reviewed on isolation procedures and properties of superoxide dismutase from Saccharomyces cerevisiae. Properties of superoxide dismutase (SOD) from yeast and SOD from macro-organisms were compared.     

Phospholipase C inhibitor from Streptoverticillium mycoheptinicum

Streptoverticillium mycoheptinicum, a producer of the antifungal antibiotic mycoheptin, was found to produce an inhibitor of Clostridium perfringens phospholipase C. Dynamics of the enzyme accumulation in the culture liquid filtrate was studied. A technique was developed for purification of the inhibitor, which includes adsorption, selective precipitation, ultrafiltration, gel chromatography and isoelectric focusing. The inhibitor was found to be of the peptide nature with the molecular weight of 3500-4000 and to exist in two isoforms with the isoelectric points of 8.15 and 8.50.     

Antipertussis immunity studied by immunoenzyme analysis

The levels of antibodies to disintegrated Bordetella pertussis and its individual fractions (protein and polysaccharide) in children immunized with different batches of adsorbed DPT vaccine have been determined with the use of EIA techniques. The background level of antibodies in the control groups has been determined, and in immunized children the levels of antibodies to disintegrated B. pertussis and its protein fraction have been shown to considerably exceed the levels of antibodies to lipopolysaccharide.     

Dependence of the specific activity of antitetanus immunoglobulin on the degree of its fragmentation

Antitetanus immunoglobulin preparations with the increasing content of Fab-fragments (15, 30, 53%) have been obtained under specific experimental conditions. Tests for specific activity have revealed an insignificant decrease (13%) in this activity in the preparation containing 15% of Fab-fragments and its sharp drop in the preparations containing 30-50% of Fab-fragments. The specific activity of antitetanus immunoglobulin has been found to be related to the degree of its fragmentation.