Social learning of hunting skills in juvenile marsh harriers <Emphasis Type="Italic">Circus aeruginosus</Emphasis>

The impact of social factors on the improvement of hunting skills of juvenile marsh harriers during their first autumnal migration were studied in SE Poland. While foraging with adult birds, juveniles performed more dives on prey both in terms of number of trials and rates. Hunting sessions of juveniles were more efficient in the presence of adults than in the absence of adults. Juveniles hunting with adults and other juveniles could select adequate habitat patches in which access to prey is easier. The role of vertical and horizontal transmission of information in the development of hunting skills in juvenile marsh harrier were confirmed because faster development of hunting ability was achieved in the social hunting after the end of their postfledging dependency period.     

Model for fitting longitudinal traits subject to threshold response applied to genetic evaluation for heat tolerance

A semi-parametric non-linear longitudinal hierarchical model is presented. The model assumes that individual variation exists both in the degree of the linear change of performance (slope) beyond a particular threshold of the independent variable scale and in the magnitude of the threshold itself; these individual variations are attributed to genetic and environmental components. During implementation via a Bayesian MCMC approach, threshold levels were sampled using a Metropolis step because their fully conditional posterior distributions do not have a closed form. The model was tested by simulation following designs similar to previous studies on genetics of heat stress. Posterior means of parameters of interest, under all simulation scenarios, were close to their true values with the latter always being included in the uncertain regions, indicating an absence of bias. The proposed models provide flexible tools for studying genotype by environmental interaction as well as for fitting other longitudinal traits subject to abrupt changes in the performance at particular points on the independent variable scale.     

Use of surface plasmon-coupled emission to measure DNA hybridization

The authors describe a new approach to measuring DNA hybridization based on surface plasmon-coupled emission (SPCE). SPCE is the resonance coupling of excited fluorophores with electron motions in thin metal films, resulting in efficient transfer of energy through the film and radiation into the glass substrate. The authors evaluated the use of SPCE for detection of DNA hybridization. An unlabeled capture biotinylated oligonucleotide was attached near the surface of a thin (50 nm) silver film using streptavidin. The authors then measured the emission intensity of single-stranded Cy5-labeled DNA upon binding to a complementary oligomer attached to a silver film. Hybridization could be detected by an increase in SPCE, which appeared as light radiated into the substrate at a sharply defined angle near 73 degrees from the normal. The largest signals were observed when the excitation angle of incidence equaled the surface plasmon wavelength, but directional emission was also observed without excitation by the surface plasmon evanescent field. The increased intensity is due to proximity to the metal surface, so that hybridization can be detected without a change in the quantum yield of the fluorophore. These results indicate that SPCE can provide highly sensitive real-time measurement of DNA hybridization.     

Metal-enhanced fluorescence: an emerging tool in biotechnology

Over the past 15 years, fluorescence has become the dominant detection/sensing technology in medical diagnostics and biotechnology. Although fluorescence is a highly sensitive technique, where single molecules can readily be detected, there is still a drive for reduced detection limits. The detection of a fluorophore is usually limited by its quantum yield, autofluorescence of the samples and/or the photostability of the fluorophores; however, there has been a recent explosion in the use of metallic nanostructures to favorably modify the spectral properties of fluorophores and to alleviate some of these fluorophore photophysical constraints. The use of fluorophore-metal interactions has been termed radiative decay engineering, metal-enhanced fluorescence or surface-enhanced fluorescence.     

Immunosuppressory activity of ubiquitin fragments containing retro-RGD sequence

A peptide fragment corresponding to the ubiquitin(50-59) sequence (LEDGRTLSDY) (U50-59) possesses a very high immunosuppressory activity, comparable to that of cyclosporine, both in the cellular and humoral immune responses. We found that the pentapeptide DGRTL (U52-56) is the shortest, effective immunosuppressory fragment of ubiquitin, although its potency is weaker than that of U50-59. Replacement of each consecutive residue with alanine in U52-56 allowed identification of essential amino acids involved in the immunosuppression. We also evaluated the roles of its N- and C-terminal groups by their acetylation and/or amidation, respectively. The active sequence is located in the external loop of the molecule and therefore it may serve as an important functional epitope for intermolecular binding. Based on the crystal structure of ubiquitin molecule, we designed and synthesized the cyclic analogue with a restricted conformation, cyclo(Glt-Gln-Leu-Glu-Asp-Gly-Arg-Thr-Leu-Ser-Asp-Lys)-NH2 (Glt = glutaryl) by reacting the C-terminal Lys side chain with the glutarylated N-terminus. The peptide was designed to mimic the ubiquitin(48-59) loop, in order to obtain the ligand that may interact with hypothetical receptors of the loop. The cyclization product selectively but strongly suppresses the cellular immune response. The results indicate that the 48-59 loop may serve as an important functional epitope in the ubiquitin molecule for intermolecular binding.     

The mimetics of antiadhesive peptides as the inhibitors of Mycobacterium kansasii phagocytosis

The alpha-guanidino acids derived of 15 proteinaceous amino acids, omega-guanidino acids with gradually increased hydrocarbon chains, and amidinated dipeptides, were tested as the mimetics of antiadhesive peptides in Mycobacteria phagocytosis inhibition. The crystal structure of omega-guanidino acids used was determined by X-ray structural analysis. It follows from our experiments that the proper distance between guanidine and carboxyl groups of effector molecules is of decisive importance for their inhibitory activity.     

The Problem of the Biologically Active Conformation of Thymopoietin

Summary The biologically active conformation of thymopoietin, based on X-ray data reported for a discontinuous thymopoietin-like motif of G-actin, is proposed.     

The New Hypothesis on Amino Acid Complementarity and its Experimental Proof

Summary During our work on the periodicity of the genetic code we proposed a new scheme of amino acid pairing [Siemion, I.Z. and Stefanowicz, P., Biosystems, 27 (1992) 77; Bull. Pol. Acad. Sci., 40 (1992) 11]. Based on this scheme, we designed and synthesized the sequences IIYTLC(Acm)GLYL(II), IIYPLC(Acm)GLYL(V), and IYPLC(Acm)GLY (VI), which are ‘antipeptides’ with respect to immunoactive fragments of TGFβ₂: YIGKTPKI (III) and YYIGKTPKIE(IV). The peptide-antipeptide interaction was investigated by electrospray ionization mass spectrometry and circular dichroism methods. The results obtained indicate that peptides interact selectively with ‘antipeptides’.     

Cyclopeptides of Linum usitatissimum.

Cyclolinopeptide A (CLA), a cyclic nonapeptide from linseed, possesses strong immunosuppressive and antimalarial activity along with the ability to inhibit cholate uptake into hepatocytes. The structure of the peptide was studied extensively in solution as well as in the solid state. It is postulated that both the Pro-Pro cis-amide bond and an 'edge-to-face' interaction between the aromatic rings of two adjacent Phe residues are important for biological activity. Structure-activity relationship studies of many linear and cyclic analogues of CLA suggest that the Pro-Xxx-Phe sequence and the flexibility of the peptide are important for the immunosuppressive activity.     

Site-specific variations in RNA folding thermodynamics visualized by 2-aminopurine fluorescence

The fluorescent base analogue 2-aminopurine (2-AP) is commonly used to study specific conformational and protein binding events involving nucleic acids. Here, combinations of steady-state and time-resolved fluorescence spectroscopy of 2-AP were employed to monitor conformational transitions within a model hairpin RNA from diverse structural perspectives. RNA substrates adopting stable, unambiguous secondary structures were labeled with 2-AP at an unpaired base, within the loop, or inside the base-paired stem. Steady-state fluorescence was monitored as the RNA hairpins made the transitions between folded and unfolded conformations using thermal denaturation, urea titration, and cation-mediated folding. Unstructured control RNA substrates permitted the effects of higher-order RNA structures on 2-AP fluorescence to be distinguished from stimulus-dependent changes in intrinsic 2-AP photophysics and/or interactions with adjacent residues. Thermodynamic parameters describing local conformational changes were thus resolved from multiple perspectives within the model RNA hairpin. These data provided energetic bases for construction of folding mechanisms, which varied among different folding-unfolding stimuli. Time-resolved fluorescence studies further revealed that 2-AP exhibits characteristic signatures of component fluorescence lifetimes and respective fractional contributions in different RNA structural contexts. Together, these studies demonstrate localized conformational events contributing to RNA folding and unfolding that could not be observed by approaches monitoring only global structural transitions.