SAXS study of crotapotin at low pH.

The structure of crotapotin, a protein extracted, from the venom of the Crotalus durissus terrificus, in solution at pH = 1.5, was studied by SAXS. The experimental results yield structural parameter values of the molecular radius of gyration Rg = 13.6 A, volume v = 16.2 x 10(3) A3 A3 and maximal dimension Dmax = 46 A. The distance distribution function deduced from the scattering measurements is consistent with an overall molecular shape of an oblate ellipsoid of revolution with asymmetry parameter v = 0.45.     

Bud break and multiple shoot formation from tissues of mature trees ofPinus caribaea andPinus kesiya

Summary Proliferation of terminal and axillary buds of 20 yr-oldPinus caribaea andP. kesiya trees was obtained on half strength DCR medium supplemented with 0.5 mg·liter^−1 6-benzylaminopurine (BA). These sprouts further elongated with the formation of multiple shoots with the ratio of 1:3, on transfer to medium in which the 0.25 mg·liter^−1 BA of the initiation medium was replaced by 0.25 mg·liter^−1 kinetin. Rooting was obtained on the same medium. Plantlets thus formed were transferred to perlite:peat:vermiculite mixture (1:1:1) in polybags (10×5 cm) under 80±5% humidity in a polyhouse. Plantlets ofP. caribaea andP. kesiya were established with 72.5 and 83.3% survival, respectively.     

Composition,Antibiofilm, and Antibacterial Potential of Volatile Oils from Geopropolis of Different Stingless Bees’ Species**

We aimed to characterize and investigate the antibacterial potential of the native stingless bees geopropolis volatile oils (VO) for the search of potentially new bioactive compounds. Geopropolis samples from Melipona bicolor schencki, M. compressipes manaosensis, M. fasciculata, M. quadrifasciata, M. marginata and M. seminigra merrillae were collected from hives in South Brazil. VO were obtained by hydrodistillation and characterised by gas chromatography coupled to mass spectrometry (GC/MS). Antimicrobial activity was assessed by microplate dilution method. The lowest MIC against cell walled bacteria was 219±0 μg mL⁻¹ from M. quadrifasciata geopropolis VO with Staphylococcus aureus. The M. b. schencki geopropolis VO minimal inhibition concentration (MIC) was 424±0 μg mL⁻¹ against all the mycoplasma strains evaluated. Fractionation resulted in the reduction of 50 % of the MIC value from the original oil. However, its compounds’ synergism seems to be essential to this activity. Antibiofilm assays demonstrated 15.25 % eradication activity and 13.20 % inhibition of biofilm formation after 24 h for one subfraction at 2× its MIC as the best results found. This may be one of the essential mechanisms by which geopropolis VOs perform their antimicrobial activity.     

PREM-1, a putative maize retroelement has LTR (long terminal repeat) sequences that are preferentially transcribed in pollen

A family of highly dispersed repetitive elements, designated PREM-1, which are transcribed primarily during pollen development, has been identified in maize. Sequence data from six PREM-1-containing genomic clones suggest that the PREM-1 sequences are the LTRs of a family of putative retroelements. PREM-1 LTRs are estimated to be present in about 10 000 to 40 000 copies in the maize genome. Although related sequences have been detected in sorghum and crab grass, highly homologous sequences appear to be specific to the genus Zea (maize and teosinte). A diverse group of RNAs that contain portions of the PREM-1 sequence at their 3 ends are transcribed in pollen; highest levels appear in early uninucleate microspores. The PREM-1-containing cDNAs do not appear to code for protein products since stop codons are present in all three reading frames. The possible significance of expression of retroelements in the male gametophyte, in terms of transposition of DNA, is discussed.     

Crystallographic and spectroscopic characterization of a molecular hinge: Conformational changes in bothropstoxin I,a dimeric Lys49-phospholipase A2 homologue

Bothropstoxin I (BthTX-I) from the venom of Bothrops jararacussuis a myotoxic phospholipase A2 (PLA2) homologue which, although catalytically inactive due to an Asp49→Lys substitution, disrupts the integrity of lipid membranes by a Ca²⁺-independent mechanism. The crystal structures of two dimeric forms of BthTX-I which diffract X-rays to resolutions of 3.1 and 2.1 Å have been determined. The monomers in both structures are related by an almost perfect twofold axis of rotation and the dimer interfaces are defined by contacts between the N-terminal α-helical regions and the tips of the β-wings of partner monomers. Significant differences in the relative orientation of the monomers in the two crystal forms results in “open” and “closed” dimer conformations. Spectroscopic investigations of BthTX-I in solution have correlated these conformational differences with changes in the intrinsic fluorescence emission of the single tryptophan residues located at the dimer interface. The possible relevance of this structural transition in the Ca²⁺-independent membrane damaging activity is discussed. Proteins 30:442–454, 1998. © 1998 Wiley-Liss, Inc.     

Modulation of NF-kappa B activity and apoptosis in chronic lymphocytic leukemia B cells

Chronic lymphocytic leukemia (CLL) is an indolent malignancy of CD5+ B lymphocytes. CLL cells express CD40, a key regulator of B cell proliferation, differentiation, and survival. In nonmalignant B cells, CD40 ligation results in nuclear translocation and activation of NF-kappaB proteins. Based on observations that in some CLL cases, the tumor cells express both CD40 and its ligand, CD154 (CD40 ligand), we proposed a model for CLL pathogenesis due to CD40 ligation within the tumor. To evaluate this issue, we used freshly isolated CLL B cells to examine constitutive and inducible NF-kappaB activity by electrophoretic mobility shift assay. We consistently observed high levels of nuclear NF-kappaB-binding activity in unstimulated CLL B cells relative to that detected in nonmalignant human B cells. In each case examined, CD40 ligation further augmented NF-kappaB activity and prolonged CLL cell survival in vitro. The principle NF-kappaB proteins in stimulated CLL cells appear to be quite similar to those in nonmalignant human B cells and include p50, p65, and c-Rel. In a CD154-positive case, blocking CD154 engagement by mAb to CD154 resulted in inhibition of NF-kappaB activity in the CLL cells. The addition of anti-CD154 mAb resulted in accelerated CLL cell death to a similar degree as was observed in cells exposed to dexamethasone. These data indicate that CD40 engagement has a profound influence on NF-kappaB activity and survival in CLL B cells, and are consistent with a role for CD154-expressing T and B cells in CLL pathogenesis. The data support the development of novel therapies based on blocking the CD154-CD40 interaction in CLL.     

Inheritance and organisation of the mitochondrial genome differ between two Saccharomyces yeasts

Petite-positive Saccharomyces yeasts can be roughly divided into the sensu stricto, including Saccharomyces cerevisiae, and sensu lato group, including Saccharomyces castellii; the latter was recently studied for transmission and the organisation of its mitochondrial genome. S. castellii mitochondrial molecules (mtDNA) carrying point mutations, which confer antibiotic resistance, behaved in genetic crosses as the corresponding point mutants of S. cerevisiae. While S. castellii generated spontaneous petite mutants in a similar way as S. cerevisiae, the petites exhibited a different inheritance pattern. In crosses with the wild type strains a majority of S. castellii petites was neutral, and the suppressivity in suppressive petites was never over 50%. The two yeasts also differ in organisation of their mtDNA molecules. The 25,753 bp sequence of S. castellii mtDNA was determined and the coding potential of both yeasts is similar. However, the S. castellii intergenic sequences are much shorter and do not contain sequences homologous to the S. cerevisiae biologically active intergenic sequences, as ori/rep/tra, which are responsible for the hyper-suppressive petite phenotype found in S. cerevisiae. The structure of one suppressive S. castellii mutant, CA38, was also determined. Apparently, a short direct intergenic repeat was involved in the generation of this petite mtDNA molecule.