Neuronal and muscular alterations caused by two wheat endosperm proteins,puroindoline-a and alpha1-purothionin,are due to ion pore formation

Using the patch-clamp technique it was found that the toxicity of the two wheat endosperm proteins puroindoline-a and alpha1-purothionin probably results from the dissipation of ion concentration gradients essential for the maintenance of cellular homeostasis.Abbreviations PIN-a puroindoline-a - PTH alpha1-purothionin Presented at the Biophysical Society Meeting on Ion Channels—from structure to disease held in May 2003, Rennes, France     

UVA-induced cyclobutane pyrimidine dimers form predominantly at thymine-thymine dipyrimidines and correlate with the mutation spectrum in rodent cells

Ligation-mediated PCR was employed to quantify cyclobutane pyrimidine dimer (CPD) formation at nucleotide resolution along exon 2 of the adenine phosphoribosyltransferase (aprt) locus in Chinese hamster ovary (CHO) cells following irradiation with either UVA (340–400 nm), UVB (295–320 nm), UVC (254 nm) or simulated sunlight (SSL; λ > 295 nm). The resulting DNA damage spectrum for each wavelength region was then aligned with the corresponding mutational spectrum generated previously in the same genetic target. The DNA sequence specificities of CPD formation induced by UVC, UVB or SSL were very similar, i.e., in each case the overall relative proportion of this photoproduct forming at TT, TC, CT and CC sites was ~28, ~26, ~16 and ~30%, respectively. Furthermore, a clear correspondence was noted between the precise locations of CPD damage hotspots, and of ‘UV signature’ mutational hotspots consisting primarily of C→T and CC→TT transitions within pyrimidine runs. However, following UVA exposure, in strong contrast to the above situation for UVC, UVB or SSL, CPDs were generated much more frequently at TT sites than at TC, CT or CC sites (57% versus 18, 11 and 14%, respectively). This CPD deposition pattern correlates well with the strikingly high proportion of mutations recovered opposite TT dipyrimidines in UVA- irradiated CHO cells. Our results directly implicate the CPD as a major promutagenic DNA photoproduct induced specifically by UVA in rodent cells.     

Roles of Saccharomyces cerevisiae DNA polymerases Poleta and Polzeta in response to irradiation by simulated sunlight

Sunlight causes lesions in DNA that if unrepaired and inaccurately replicated by DNA polymerases yield mutations that result in skin cancer in humans. Two enzymes involved in translesion synthesis (TLS) of UV-induced photolesions are DNA polymerase η (Polη) and polymerase ζ (Polζ), encoded by the RAD30A and REV3 genes, respectively. Previous studies have investigated the TLS roles of these polymerases in human and yeast cells irradiated with monochromatic, short wavelength UVC radiation (254 nm). However, less is known about cellular responses to solar radiation, which is of higher and mixed wavelengths (310–1100 nm) and produces a different spectrum of DNA lesions, including Dewar photoproducts and oxidative lesions. Here we report on the comparative cytotoxic and mutagenic effects of simulated sunlight (SSL) and UVC radiation on yeast wild-type, rad30Δ, rev3Δ and rev3Δ rad30Δ strains. The results with SSL support several previous interpretations on the roles of these two polymerases in TLS of photodimers and (6–4) photoproducts derived from studies with UVC. They further suggest that Polη participates in the non-mutagenic bypass of SSL-dependent cytosine-containing Dewar photoproducts and 8-oxoguanine, while Polζ is mainly responsible for the mutagenic bypass of all types of Dewar photoproducts. They also suggest that in the absence of Polζ, Polη contributes to UVC- and SSL-induced mutagenesis, possibly by the bypass of photodimers containing deaminated cytosine.     

The redox protein construction kit: pre-last universal common ancestor evolution of energy-conserving enzymes

Genome analyses and the resolution of three-dimensional structures have provided evidence in recent years for hitherto unexpected family relationships between redox proteins of very diverse enzymes involved in bioenergetic electron transport. Many of these enzymes appear in fact to be constructed from only a limited set of building blocks. Phylogenetic analysis of selected units from this "redox enzyme construction kit" indicates an origin for several prominent bioenergetic enzymes that is very early, lying before the divergence of Bacteria and Archaea. Possible scenarios for the early evolution of selected complexes are proposed based on the obtained tree topologies.     

A maurotoxin with constrained standard disulfide bridging: innovative strategy of chemical synthesis,pharmacology, and docking on K+ channels

Maurotoxin (MTX) is a 34-residue toxin that has been isolated initially from the venom of the scorpion Scorpio maurus palmatus. It presents a large number of pharmacological targets, including small conductance Ca2+-activated and voltage-gated K+ channels. Contrary to other toxins of the alpha-KTx6 family (Pi1, Pi4, Pi7, and HsTx1), MTX exhibits a unique disulfide bridge organization of the type C1-C5, C2-C6, C3-C4, and C7-C8 (instead of the conventional C1-C5, C2-C6, C3-C7, and C4-C8, herein referred to as Pi1-like) that does not prevent its folding along the classic alpha/beta scaffold of scorpion toxins. Here, we developed an innovative strategy of chemical peptide synthesis to produce an MTX variant (MTXPi1) with a conventional pattern of disulfide bridging without any alteration of the toxin chemical structure. This strategy was used solely to address the impact of half-cystine pairings on MTX structural properties and pharmacology. The data indicate that MTXPi1 displays some marked changes in affinities toward the target K+ channels. Computed docking analyses using molecular models of both MTXPi1 and the various voltage-gated K+ channel subtypes (Shaker B, Kv1.2, and Kv1.3) were found to correlate with MTXPi1 pharmacology. A functional map detailing the interaction between MTXPi1 and Shaker B channel was generated in line with docking experiments.     

A novel nuclear export signal and a REF interaction domain both promote mRNA export by the Epstein-Barr virus EB2 protein

A striking characteristic of mRNA export factors is that they shuttle continuously between the cytoplasm and the nucleus. This shuttling is mediated by specific factors interacting with peptide motifs called nuclear export signals (NES) and nuclear localization signals. We have identified a novel CRM-1-independent transferable NES and two nuclear localization signals in the Epstein-Barr virus mRNA export factor EB2 (also called BMLF1, Mta, or SM) localized at the N terminus of the protein between amino acids 61 and 146. We have also found that a previously described double NES (amino acids 213-236) does not mediate the nuclear shuttling of EB2, but is an interaction domain with the cellular export factor REF in vitro. This newly characterized REF interaction domain is essential for EB2-mediated mRNA export. Accordingly, in vivo, EB2 is found in complexes containing REF as well as the cellular factor TAP. However, these interactions are RNase-sensitive, suggesting that the RNA is an essential component of these complexes.     

Yeast epiarginase regulation,an enzyme-enzyme activity control: identification of residues of ornithine carbamoyltransferase and arginase responsible for enzyme catalytic and regulatory activities

In the presence of ornithine and arginine, ornithine carbamoyltransferase (OTCase) and arginase form a one-to-one enzyme complex in which the activity of OTCase is inhibited whereas arginase remains catalytically active. The mechanism by which these nonallosteric enzymes form a stable complex triggered by the binding of their respective substrates raises the question of how such a cooperative association is induced. Analyses of mutations in both enzymes identify residues that are required for their association, some of them being important for catalysis. In arginase, two cysteines at the C terminus of the protein are crucial for its epiarginase function but not for its catalytic activity and trimeric structure. In OTCase, mutations of putative ornithine binding residues, Asp-182, Asn-184, Asn-185, Cys-289, and Glu-256 greatly reduced the affinity for ornithine and impaired the interaction with arginase. The four lysine residues located in the SMG loop, Lys-260, Lys-263, Lys-265, and Lys-268, also play an important role in mediating the sensitivity of OTCase to ornithine and to arginase and appear to be involved in transducing and enhancing the signal given by ornithine for the closure of the catalytic domain.     

Solution structure of the recombinant penaeidin-3, a shrimp antimicrobial peptide

Penaeidins are a family of antimicrobial peptides of 47-63 residues isolated from several species of shrimp. These peptides display a proline-rich domain (N-terminal part) and a cysteine-rich domain (C-terminal part) stabilized by three conserved disulfide bonds whose arrangement has not yet been characterized. The recombinant penaeidin-3a of Litopenaeus vannamei (63 residues) and its [T8A]-Pen-3a analogue were produced in Saccharomyces cerevisiae and showed similar antimicrobial activity. The solution structure of the [T8A]-Pen-3a analogue was determined by using two-dimensional 1H NMR and simulated annealing calculations. The proline-rich domain, spanning residues 1-28 was found to be unconstrained. In contrast, the cysteine-rich domain, spanning residues 29-58, displays a well defined structure, which consists of an amphipathic helix (41-50) linked to the upstream and the downstream coils by two disulfide bonds (Cys32-Cys47 and Cys48-Cys55). These two coils are in turn linked together by the third disulfide bond (Cys36-Cys54). Such a disulfide bond packing, which is in agreement with the analysis of trypsin digests by ESI-MS, contributes to the highly hydrophobic core. Side chains of Arg45 and Arg50, which belong to the helix, and side chains of Arg37 and Arg53, which belong to the upstream and the downstream coils, are located in two opposite parts of this globular and compact structure. The environment of these positively charged residues, either by hydrophobic clusters at the surface of the cysteine-rich domain or by sequential hydrophobic residues in the unconstrained proline-rich domain, gives rise to the amphipathic character required for antimicrobial peptides. We hypothesize that the antimicrobial activity of penaeidins can be explained by a cooperative effect between the proline-rich and cysteine-rich features simultaneously present in their sequences.     

Slit antagonizes netrin-1 attractive effects during the migration of inferior olivary neurons

Inferior olivary neurons (ION) migrate circumferentially around the caudal rhombencephalon starting from the alar plate to locate ventrally close to the floor-plate, ipsilaterally to their site of proliferation. The floor-plate constitutes a source of diffusible factors. Among them, netrin-1 is implied in the survival and attraction of migrating ION in vivo and in vitro. We have looked for a possible involvement of slit-1/2 during ION migration. We report that: (1) slit-1 and slit-2 are coexpressed in the floor-plate of the rhombencephalon throughout ION development; (2) robo-2, a slit receptor, is expressed in migrating ION, in particular when they reach the vicinity of the floor-plate; (3) using in vitro assays in collagen matrix, netrin-1 exerts an attractive effect on ION leading processes and nuclei; (4) slit has a weak repulsive effect on ION axon outgrowth and no effect on migration by itself, but (5) when combined with netrin-1, it antagonizes part of or all of the effects of netrin-1 in a dose-dependent manner, inhibiting the attraction of axons and the migration of cell nuclei. Our results indicate that slit silences the attractive effects of netrin-1 and could participate in the correct ventral positioning of ION, stopping the migration when cell bodies reach the floor-plate.