Antiamoebin I in methanol solution: rapid exchange between right-handed and left-handed 3(10)-helical conformations

Antiamoebin I (Aam-I) is a membrane-active peptaibol antibiotic isolated from fungal species belonging to the genera Cephalosporium, Emericellopsis, Gliocladium, and Stilbella. Antiamoebin I has the amino acid sequence: Ac-Phe(1)-Aib-Aib-Aib-Iva-Gly-Leu-Aib(8)-Aib-Hyp-Gln-Iva-Hyp-Aib-Pro-Phl(16). By using the uniformly (13)C,(15)N-labeled sample of Aam-I, the set of conformationally dependent J couplings and (3h)J(NC) couplings through H-bonds were measured. Analysis of these data along with the data on magnetic nonequivalence of the (13)C(beta) nuclei (Deltadelta((13)C(beta))) in Aib and Iva residues allowed us to draw the univocal conclusion that the N-terminal part (Phe(1)-Gly(6)) of Aam-I in MeOH solution is in fast exchange between the right-handed and left-handed 3(10)-helical conformations, with an approximately equal population of both states. An additional conformational exchange process was found at the Aib(8) residue. The (15)N-NMR-relaxation and CD-spectroscopy measurements confirmed these findings. Molecular modeling and Monte Carlo simulations revealed that both exchange processes are correlated and coupled with significant hinge-bending motions around the Aib(8) residue. Our results explain relatively low activity of Aam-I with respect to other 15-amino acid residue peptaibols (for example, zervamicin) in functional and biological tests. The high dynamic 'propensity' possibly prevents both initial binding of the antiamoebin to the membrane and subsequent formation of stable ionic channels according to the barrel-stave mechanism.     

Comparative study of the "membrane reserve" of blood cells of reptiles and mammals

Based on the method of hypoosmotic loads, the value of membrane reserve and its use by blood cells of reptiles and mammals have been studied. It has been shown that lymphocytes of the both animal species have the highest reserve of plasmalemma, while frog heterophils - the lowest one. A significantly lower part of the membrane reserve participates in formation of phagosomes by mammalian neutrophils as compared with amphibian erythrocytes.     

Horseradish peroxidase. XXXIV. Oxidation of compound II to I by periodate and inorganic anion radicals.

The one-electron oxidation of horseradish peroxidase compound II to compound I by sodium periodate was observed. The bimolecular rate constant for the NaIO4--compound II interaction is equal to 9.5 +/- 1 x 10(-3) M-1s-1 at room temperature. Irradiation, using ultraviolet light, of the solution containing compound II and persulfate in the presence of bicarbonate, chloride, or bromide, leads ot the fast accumulation of compound I due to the oxidative action of SO4, CO3, Cl2, and Br2 anion radicals, which are products of the photolysis.     

Nucleotide sequences of long terminal repeats of the human endogenous retrovirus (LTR HERV-K) on the short arm of chromosome 7: identification,analysis and evaluation of transcriptional activity

Six clones containing long terminal repeat (LTR) sequences of human endogenous retrovirus of the HERV-K family were found in the YAC library (1200 kb) of the short arm of human chromosome 7. The sequence sizes of the three clones corresponded to the full-length LTR (969 bp). The LTR localization was determined using FISH and verified by comparison with the GenBank database. All three DNA fragments containing solitary LTRs were transcribed in normal germline cells (testicular parenchyma tissue). The differences in the expression of these clones in the germline tumor cells (seminoma) were observed.     

Recombinant expression, synthesis, purification, and solution structure of arenicin

Arenicins are 21-residue cationic antimicrobial peptides, isolated from marine polychaeta Arenicola marina. In order to determine a high-resolution three-dimensional structure of arenicin-2, the recombinant peptide was overexpressed as a fused form in Escherichia coli. Both arenicin isoforms were synthesized using the Fmoc-based solid-phase strategy. Recombinant and synthetic arenicins were purified, and their antimicrobial and spectroscopic properties were analyzed. NMR investigation shows that in water solution arenicin-2 displays a prolonged beta-hairpin, formed by two antiparallel beta-strands and stabilized by one disulfide and nine hydrogen bonds. A significant right-handed twist in the beta-sheet is deprived the peptide surface of amphipathicity. CD spectroscopic analysis indicates that arenicin-2 binds to the SDS and DPC micelles, and conformation of the peptide is significantly changed upon binding. Arenicin strongly binds to anionic lipid (POPE/POPG) vesicles in contrast with zwitterionic (POPC) ones. These results suggest that arenicins are membrane active peptides and point to possible mechanism of their selectivity toward bacterial cells.     

Modular toxin from the lynx spider Oxyopes takobius: Structure of spiderine domains in solution and membrane‐mimicking environment

We have recently demonstrated that a common phenomenon in evolution of spider venom composition is the emergence of so‐called modular toxins consisting of two domains, each corresponding to a “usual” single‐domain toxin. In this article, we describe the structure of two domains that build up a modular toxin named spiderine or OtTx1a from the venom of Oxyopes takobius. Both domains were investigated by solution NMR in water and detergent micelles used to mimic membrane environment. The N‐terminal spiderine domain OtTx1a‐AMP (41 amino acid residues) contains no cysteines. It is disordered in aqueous solution but in micelles, it assumes a stable amphiphilic structure consisting of two α‐helices separated by a flexible linker. On the contrary, the C‐terminal domain OtTx1a‐ICK (59 residues) is a disulfide‐rich polypeptide reticulated by five S–S bridges. It presents a stable structure in water and its core is the inhibitor cystine knot (ICK) or knottin motif that is common among single‐domain neurotoxins. OtTx1a‐ICK structure is the first knottin with five disulfide bridges and it represents a good reference for the whole oxytoxin family. The affinity of both domains to membranes was measured with NMR using titration by liposome suspensions. In agreement with biological tests, OtTx1a‐AMP was found to show high membrane affinity explaining its potent antimicrobial properties.     

NMR structure of a full-length single-pass membrane protein NRADD

Structural study of any single-pass membrane protein is both an important and challenging task. In this report, we present the structure of a neurotrophin receptor-alike death-domain protein. The structure and dynamics of the protein was investigated by conventional nuclear magnetic resonance techniques in the solution of phospholipid bicelles. The receptor contains two folded regions—α-helical transmembrane domain and globular C-terminal death domain with more than 50% of the rest of backbone being disordered. This is the first structure of a full-length single-pass membrane receptor-alike protein solved by the single method.