Panorama of the Intracellular Molecular Concert Orchestrated by Actinoporins, Pore-Forming Toxins from Sea Anemones

Actinoporins (APs) are soluble pore-forming proteins secreted by sea anemones that experience conformational changes originating in pores in the membranes that can lead to cell death. The processes involved in the binding and pore-formation of members of this protein family have been deeply examined in recent years; however, the intracellular responses to APs are only beginning to be understood. Unlike pore formers of bacterial origin, whose intracellular impact has been studied in more detail, currently, we only have knowledge of a few poorly integrated elements of the APs’ intracellular action. In this review, we present and discuss an updated landscape of the studies aimed at understanding the intracellular pathways triggered in response to APs attack with particular reference to sticholysin II, the most active isoform produced by the Caribbean Sea anemone Stichodactyla helianthus. To achieve this, we first describe the major alterations these cytolysins elicit on simpler cells, such as non-nucleated mammalian erythrocytes, and then onto more complex eukaryotic cells, including tumor cells. This understanding has provided the basis for the development of novel applications of sticholysins such as the construction of immunotoxins directed against undesirable cells, such as tumor cells, and the design of a cancer vaccine platform. These are among the most interesting potential uses for the members of this toxin family that have been carried out in our laboratory.

Sticholysins, pore-forming proteins from a marine anemone can induce maturation of dendritic cells through a TLR4 dependent-pathway

Sticholysins (Sts) I and II (StI and StII) are pore-forming proteins (PFPs), purified from the Caribbean Sea anemone Stichodactyla helianthus. StII encapsulated into liposomes induces a robust antigen-specific cytotoxic CD8⁺ T lymphocytes (CTL) response and in its free form the maturation of bone marrow-derived dendritic cells (BM-DCs). It is probable that the latter is partially supporting in part the immunomodulatory effect on the CTL response induced by StII-containing liposomes. In the present work, we demonstrate that the StII's ability of inducing maturation of BM-DCs is also shared by StI, an isoform of StII. Using heat-denatured Sts we observed a significant reduction in the up-regulation of maturation markers indicating that both PFP's ability to promote maturation of BM-DCs is dependent on their conformational characteristics. StII-mediated DC maturation was abrogated in BM-DCs from toll-like receptor (TLR) 4 and myeloid differentiation primary response gene 88 (MyD88)-knockout mice but not in cells from TLR2-knockout mice. Furthermore, the antigen-specific CTL response induced by StII-containing liposomes was reduced in TLR4-knockout mice. These results indicate that StII, and probably by extension StI, has the ability to induce maturation of DCs through a TLR4/MyD88-dependent pathway, and that this activation contributes to the CTL response generated by StII-containing liposomes.

Self-association and folding in membrane determine the mode of action of peptides from the lytic segment of sticholysins

Sticholysin I and II (Sts: St I and St II) are proteins of biomedical interest that form pores upon the insertion of their N-terminus in the plasma membrane. Peptides spanning the N-terminal residues of StI (StI_1-31) or StII (StII_1-30) can mimic the permeabilizing ability of these toxins, emerging as candidates to rationalize their potential biomedical applications. These peptides have different activities that correlate with their hydrophobicity. However, it is not clear how this property contributes to peptide folding in solution or upon binding to membranes. Here we compared the conformational properties of these peptides and shorter versions lacking the hydrophobic segment 1-11 of StI (StI_12-31) or 1-10 of StII (StII_11-30). Folding of peptides was assessed in solution and in membrane mimetic systems and related with their ability to bind to membranes and to permeabilize lipid vesicles. Our results suggest that the differences in activity among peptides could be ascribed to their different folding propensity and different membrane binding properties. In solution, StII_1-30 tends to acquire α-helical conformation coexisting with self-associated structures, while StI_1-31 remains structureless. Both peptides fold as α-helix in membrane; but StII_1-30 also self-associates in the lipid environment, a process that is favored by its higher affinity for membrane. We stress the contribution of the non-polar/polar balance of the 1-10 amino acid sequence of the peptides as a determining factor for different self-association capabilities. Such difference in hydrophobicity seems to determine the molecular path of peptides folding upon binding to membranes, with an impact in their permeabilizing activity. This study contributes to a better understanding of the molecular mechanisms underlying the permeabilizing activity of Sts N-terminal derived peptides, with connotation for the exploitation of these small molecules as alternative of the full-length toxins in clinical settings.

Novel Adjuvant Based on the Pore-Forming Protein Sticholysin II Encapsulated into Liposomes Effectively Enhances the Antigen-Specific CTL-Mediated Immune Response

Vaccine strategies to enhance CD8⁺ CTL responses remain a current challenge because they should overcome the plasmatic and endosomal membranes for favoring exogenous Ag access to the cytosol of APCs. As a way to avoid this hurdle, sticholysin (St) II, a pore-forming protein from the Caribbean Sea anemone Stichodactyla helianthus, was encapsulated with OVA into liposomes (Lp/OVA/StII) to assess their efficacy to induce a CTL response. OVA-specific CD8⁺ T cells transferred to mice immunized with Lp/OVA/StII experienced a greater expansion than when the recipients were injected with the vesicles without St, mostly exhibiting a memory phenotype. Consequently, Lp/OVA/StII induced a more potent effector function, as shown by CTLs, in vivo assays. Furthermore, treatment of E.G7-OVA tumor-bearing mice with Lp/OVA/StII significantly reduced tumor growth being more noticeable in the preventive assay. The contribution of CD4⁺ and CD8⁺ T cells to CTL and antitumor activity, respectively, was elucidated. Interestingly, the irreversibly inactive variant of the StI mutant StI W111C, encapsulated with OVA into Lp, elicited a similar OVA-specific CTL response to that observed with Lp/OVA/StII or vesicles encapsulating recombinant StI or the reversibly inactive StI W111C dimer. These findings suggest the relative independence between StII pore-forming activity and its immunomodulatory properties. In addition, StII-induced in vitro maturation of dendritic cells might be supporting these properties. These results are the first evidence, to our knowledge, that StII, a pore-forming protein from a marine eukaryotic organism, encapsulated into Lp functions as an adjuvant to induce a robust specific CTL response.

The Presence of Sterols Favors Sticholysin I-Membrane Association and Pore Formation Regardless of Their Ability to Form Laterally Segregated Domains

Sticholysin I (St I) is a pore-forming toxin (PFT) produced by the Caribbean Sea anemone Stichodactyla helianthus belonging to the actinoporin protein family, a unique class of eukaryotic PFT. As for actinoporins, it has been proposed that the presence of cholesterol (Chol) and the coexistence of lipid phases increase binding to the target membrane and pore-forming ability. However, little is known about the role of membrane structure and dynamics (phase state, fluidity, and the presence of lipid domains) on the activity of actinoporins or which regions of the membrane are the most favorable for protein insertion, oligomerization, and eventually pore formation. To gain insight into the role of membrane properties on the functional activity of St I, we studied its binding to monolayers and vesicles of phosphatidylcholine (PC), sphingomyelin (SM), and sterols inducing (ergosterol -Erg and cholesterol -Chol) or not (cholestenone - Cln) membrane phase segregation in liquid ordered (Lo) and liquid disordered (Ld) domains. This study revealed that St I binds and permeabilizes with higher efficiency sterol-containing membranes independently of their ability to form domains. We discuss the results in terms of the relevance of different membrane properties for the actinoporins mechanism of action, namely, molecular heterogeneity, specially potentiated in membranes with sterols inducers of phase separation (Chol or Erg) or Cln, a sterol noninducer of phase separation but with a high propensity to induce nonlamellar phase. The role of the Ld phase is pointed out as the most suitable platform for pore formation. In this regard, such regions in Chol-containing membranes seem to be the most favored due to its increased fluidity; this property promotes toxin insertion, diffusion, and oligomerization leading to pore formation.

Inactivation of the pore-forming toxin Sticholysin I by peroxynitrite: protection by cys groups incorporated in the toxin

Sea anemones synthesize a variety of toxic peptides and proteins of biological interest. The Caribbean Sea anemone Stichodactyla helianthus, produces two pore-forming toxins, Sticholysin I (St I) and Stichloysin II (St II), with the ability to form oligomeric pores in cell and lipid bilayers characteristically lacking cysteine in their amino acid sequences. Recently, two mutants of a recombinant variant of Sticholysin I (rSt I) have been obtained with a Cys residue in functionally relevant regions for the pore-forming activity of the toxin: r St I F15C (in the amino terminal sequence) and r St I R52C (in the binding site). Aiming at characterizing the effects of oxidants in toxins devoid (r St I) or containing -SH moieties (r St I F15C and r St I R52C), we measured their hemolytic activity and pore forming capacity prior and after their incubation with peroxynitrite (ONOO(-)). At low ONOO(-)/Toxin ratios, nearly 0.8 Trp groups are modified by each added peroxynitrite molecule, and the toxin activity is reduced in ca. 20 %. On the other hand, in -SH bearing mutants only 0.5 Trp groups are modified by each peroxynitrite molecule and the toxin activity is only reduced in 10 %. The results indicated that Cys is the initial target of the oxidative damage and that Trp residues in Cys-containing toxins were less damaged than those in r St I. This relative protection of Trp groups correlates with a smaller loss of hemolytic activity and permeabilization ability in liposomes and emphasizes the relevance of Trp groups in the pore forming capacity of the toxins.

Solution NMR analysis of the interaction between the actinoporin sticholysin I and DHPC micelles--correlation with backbone dynamics

Sticholysin I (StI), an actinoporin expressed as a water-soluble protein by the sea anemone Stichodactyla helianthus, binds to natural and model membranes, forming oligomeric pores. It is proposed that the first event of a multistep pore formation mechanism consists of the monomeric protein attachment to the lipid bilayer. To date there is no high-resolution structure of the actinoporin pore or other membrane-bound form available. Here we evaluated StI:micelle complexes of variable lipid composition to look for a suitable model for NMR studies. Micelles of pure or mixed lysophospholipids and of dihexanoyl phosphatidylcholine (DHPC) were examined. The StI:DHPC micelle was found to be the best system, yielding a stable sample and good quality spectra. A comprehensive chemical shift perturbation analysis was performed to map the StI membrane recognition site in the presence of DHPC micelles. The region mapped (residues F(51), R(52), S(53) in loop 3; F(107), D(108), Y(109), W(111), Y(112), W(115) in loop 7; Q(129), Y(132), D(134), M(135), Y(136), Y(137), G(138) in helix-α2) is in agreement with previously reported data, but additional residues were found to interact, especially residues V(81), A(82), T(83), G(84) in loop 5, and A(85), A(87) in strand-β5. Backbone dynamics measurements of StI free in solution and bound to micelles highlighted the relevance of protein flexibility for membrane binding and suggested that a conformer selection process may take place during protein-membrane interaction. We conclude that the StI:DHPC micelles system is a suitable model for further characterization of an actinoporin membrane-bound form by solution NMR.

Effect of human serum albumin upon the permeabilizing activity of sticholysin II, a pore forming toxin from Stichodactyla heliantus

Sticholysin II (St II) is a haemolytic toxin isolated from the sea anemone Stichodactyla helianthus. The high haemolytic activity of this toxin is strongly dependent on the red cell status and the macromolecule conformation. In the present communication we evaluate the effect of human serum albumin on St II haemolytic activity and its capacity to form pores in the bilayer of synthetic liposomes. St II retains its pore forming capacity in the presence of large concentrations (up to 500 μM) of human serum albumin. This effect is observed both in its capacity to produce red blood cells haemolysis and to generate functional pores in liposomes. In particular, the capacity of the toxin to lyse red blood cells increases in the presence of human serum albumin (HSA). Regarding the rate of the pore forming process, it is moderately decreased in liposomes and in red blood cells, in spite of an almost total coverage of the interface by albumin. All the data obtained in red cells and model membranes show that St II remains lytically active even in the presence of high HSA concentrations. This stubbornness can explain why the toxin is able to exert its haemolytic activity on membranes immersed in complex plasma matrixes such as those present in living organisms.

Validation of a mutant of the pore-forming toxin sticholysin-I for the construction of proteinase-activated immunotoxins

The use of pore-forming toxins from sea anemones (actinoporins) in the construction of immunotoxins (ITs) against tumour cells is an alternative for cancer therapy. However, the main disadvantage of actinoporin-based ITs obtained so far has been the poor cellular specificity associated with the toxin's ability to bind and exert its activity in almost any cell membrane. Our final goal is the construction of tumour proteinase-activated ITs using a cysteine mutant at the membrane binding region of sticholysin-I (StI), a cytolysin isolated from the sea anemone Stichodactyla helianthus. The mutant and the ligand moiety would be linked by proteinase-sensitive peptides through the StI cysteine residue blocking the toxin binding region and hence the IT non-specific killing activity. To accomplish this objective the first step was to obtain the mutant StI W111C, and to evaluate the impact of mutating tryptophan 111 by cysteine on the toxin pore-forming capacity. After proteolysis of the cleavage sequence, a short peptide would remain attached to the toxin. The next step was to evaluate whether this mutant is able to form pores even with a residual peptide linked to cysteine 111. In this work we demonstrated that (i) StI W111C shows pore-forming capacity in a nanomolar range, although it is 8-fold less active than the wild-type recombinant StI, corroborating the previously reported importance of residue 111 for the binding of StI to membranes, and (ii) the mutant is able to form pores even with a residual seven-residue peptide linked to cysteine 111. In addition, it was demonstrated that binding of a large molecule to cysteine 111 renders an inactive toxin that is no longer able to bind to the membrane. These results validate the mutant StI W111C for its use in the construction of tumour proteinase-activated ITs.

Phenotypic Characteristics and Virulence of Vibrio anguillarum-Related Organisms

The phenotypic, molecular, and virulence properties of 46 Vibrio anguillarum-related (VAR) strains isolated from diseased fish and shellfish and from the environment were investigated. Twelve reference strains belonging to the 10 serotypes of V. anguillarum and the Vibrio splendidus type strain were included for comparison. Numerical taxonomy studies allowed us to group the isolates into four phena. The main phenotypic traits to differentiate VAR strains from V. anguillarum were fermentation of arabinose and mannitol, indole and Voges-Proskauer reactions, gelatin and casein hydrolysis, hemolytic activity, growth at 37 and 4 degrees C, and resistance to ampicillin. Serological analysis confirmed that phena I and II were composed mainly of strains of V. anguillarum, while phena III and IV included VAR strains. Excluding the reference strains, the typeable isolates belonged to serotypes O3 (15 strains), O4 (3 strains), and O5 (2 strains) of V. anguillarum. The infectivity trials showed that only 9 of a total of 24 strains tested displayed virulence for rainbow trout. Virulent strains (50% lethal dose ranging from 10 to 10 cells) included V. anguillarum strains belonging to serotypes O1 (one strain), O2 (one strain), O3 (three isolates), and O4 (one isolate) and only three strains of the VAR group. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of lipopolysaccharide and outer membrane proteins showed heterogeneity not only among the 10 V. anguillarum serotypes but also within the VAR group. Immunoblot assays demonstrated a close relationship among V. anguillarum strains from the same serotype, while strains from different serotypes were not antigenically related. The VAR strains did not share antigenic components with the serotypes of V. anguillarum tested (serotypes O1 to O5). Plasmids were detected in only 19 of the total of 59 strains. The majority of the strains carrying plasmids were grouped within phenon IV, in which plasmid bands of 27 and 36 MDa were found in all the isolates. No correlation between the plasmid content of VAR microorganisms and their phenotypic or virulence characteristics was observed. From these results it can be concluded that VAR strains associated with disease should be included together with V. anguillarum in the formulation of vaccines against vibriosis.

Fatty acid analysis as a chemotaxonomic tool for taxonomic and epidemiological characterization of four fish pathogenic Tenacibaculum species

AIMS

In this work, fatty acid content and profiles were analysed in order to differentiate the species Tenacibaculum maritimum, Tenacibaculum gallaicum, Tenacibaculum discolor and Tenacibaculum ovolyticum that are pathogenic for cultured marine fish and to assess the potential of fatty acid profiles as a tool for epizootiological typing.

METHODS AND RESULTS

The fatty acid methylesters (FAMEs) were extracted from cells grown on marine agar for 48 h at 25 degrees C and were prepared and analysed according to the standard protocol of the MIDI/Hewlett Packard Microbial Identification System. The cellular fatty acid profiles of Tenacibaculum strains tested were characterized by the presence of large amounts of branched (36.1-40.2%) and hydroxylated (29.6-31.7%) fatty acids. The FAME products from the four species significantly (P < 0.05) differed in the content of iso-C(15:0)3-OH, iso-C(16:0)3-OH, iso-C(15:1)G, summed feature 3 (a component that contains C(16:1)omega7c and/or iso-C(15:0) 2-OH), iso-C(16:0), C(17:1)omega6c, C(15:0)3-OH, iso-C(17:0)3-OH.

CONCLUSIONS

Results of present study demonstrated the existence of differences in the fatty acids content between the T. maritimum isolates from different marine fish/geographical origin and between strains of T. maritimum, T. discolor, T. gallaicum and T. ovolyticum.

SIGNIFICANCE AND IMPACT OF THE STUDY

Profiling of fatty acids may be a useful tool to distinguish T. maritimum from other Tenacibaculum species pathogenic for fish as well as for epizootiological differentiation of T. maritimum isolates.

Sticholysins I and II interaction with cationic micelles promotes toxins’ conformational changes and enhanced hemolytic activity

The effect of three cationic surfactants bearing the same polar head group and different chain length (cetyltrimethyl ammonium bromide (CTAB); tetradecyltrimethylammonium bromide (TTAB); dodecyltrimethylammonium bromide (DTAB)) on the conformation and function of the sea anemone pore-forming toxins sticholysins I and II (St I and St II) was studied by fluorescence and circular dichroism spectroscopy and evaluation of hemolytic activity (HA). Preincubation of the toxins with the longer chain surfactants CTAB and TTAB at concentrations slightly above their critical micelle concentration (CMC) leads to an enhancement of their HA. Significant increases in the fluorescence intensity with a slightly red shift in lambda(max) were observed at concentrations close to the surfactants' CMC, suggesting changes in the environment of the tryptophan residues. The changes in the fluorescence intensity are more noticeable and take place at lower surfactant concentrations for St I, irrespective of the surfactant alkyl chain length, although the differences between St I and St II increase as the surfactant alkyl chain length increases. This is evinced not only by the higher fluorescence intensity values and the lower surfactant concentrations required to reach them, but also by the higher acrylamide-quenching constant values (Ksv) for St I. However, the surfactant's effects on the toxins' HA were not found to be directly related to the observed changes in fluorescence intensity, as well as near- and far-UV-CD spectra. In particular, the latter spectra indicate that changes in HA and in fluorescence behavior take place without noticeable modifications in St I and St II secondary and tertiary structures. The results suggest that the interaction with the surfactants induces only subtle conformational changes in the toxins that favor the formation of lytic competent structures.

Effect of sphingomyelin and cholesterol on the interaction of St II with lipidic interfaces

Sticholysin II (St II) is a cytolysin produced by the sea anemone Stichodactyla helianthus, characterized by forming oligomeric pores in natural and artificial membranes. In the present work the influence of the membrane lipidic components sphingomyelin (SM) and cholesterol (Cho) on binding and functional activity of St II, was evaluated using ELISA, lipid monolayers and liposomes. The aim of this work was to establish the promoting role of Cho and SM, both in St II binding and pore formation efficiency. In general the association (evaluated by ELISA and incorporation to phospholipid monolayers) of St II to lipids mixtures was better than to any one of the single components. Regarding the unique role of SM, it was found that, albeit inefficiently, St II binds to phosphatidylcholine (PC):Cho monolayers and liposomes, and is able to form active pores in these bilayers. The results in monolayers and liposomes show that the presence of SM and large amounts of Cho leads to the highest values of critical pressure and rate of association to monolayers, the most favorable interaction with liposomes, and the fastest rate of pore formation, in spite of the rigidity of the layers as suggested by the high generalized polarization (GP) of Laurdan incorporated to liposomes and FTIR data. Taken together, the present results show that the joint presence of SM and Cho, both in binary and ternary (PC containing) mixtures provide conditions particularly suitable for St II binding and function. We suggest that microdomains present in the bilayers could be important for toxin-membrane association.

Structural and functional characterization of a recombinant sticholysin I (rSt I) from the sea anemone Stichodactyla helianthus

Sticholysins I and II (Sts I and II) are two potent cytolysins from the sea anemone Stichodactyla helianthus. These isoforms present 13 substitutions, with three non-conservative located at the N-terminus. St II is considerably more hemolytic than St I in human red blood cells, a result explained by the smaller number of negatively charged groups present at St II's N-terminus. In the present work, we have obtained a recombinant St I (rSt I), differing from the wild type in a single amino acid residue (E16Q). This pseudo-wild type is structurally similar to St I and shows a similar capacity to interact with and form pores in model membranes. This was assessed by the intrinsic fluorescence increase in the presence of liposomes, their adsorption to bilayers (measured by SPR), their concentration at the air-water interface, their interaction with lipid monolayers and their capacity to promote the release of carboxyfluorescein entrapped in liposomes. In spite of these similarities, rSt I presents a larger hemolytic activity in human red blood cells than St I, being intermediate in activity between Sts I and II. The results obtained in the present work emphasize that even the change of one single E by Q at the N-terminal segment may modify the toxin HA and show that this functional property is the most sensitive to subtle changes in the protein primary structure.

Model peptides mimic the structure and function of the N-terminus of the pore-forming toxin sticholysin II

To investigate the role of the N-terminal region in the lytic mechanism of the pore-forming toxin sticholysin II (St II), we studied the conformational and functional properties of peptides encompassing the first 30 residues of the protein. Peptides containing residues 1-30 (P1-30) and 11-30 (P11-30) were synthesized and their conformational properties were examined in aqueous solution as a function of peptide concentration, pH, ionic strength, and addition of the secondary structure-inducing solvent trifluoroethanol (TFE). CD spectra showed that increasing concentration, pH, and ionic strength led to aggregation of P1-30; as a consequence, the peptide acquired beta-sheet conformation. In contrast, P11-30 exhibited practically no conformational changes under the same conditions, remaining essentially structureless. Moreover, this peptide did not undergo aggregation. These differences clearly point to the modulating effect of the first 10 hydrophobic residues on the peptides aggregation and conformational properties. In TFE both the first ten hydrophobic peptides acquired alpha-helical conformation, albeit to a different extent, P11-30 displayed lower alpha-helical content. P1-30 presented a larger fraction of residues in alpha-helical conformation in TFE than that found in St II's crystal structure for that portion of the protein. Since TFE mimics the membrane environment, such increase in helical content could also occur upon toxin binding to membranes and represent a step in the mechanism of pore formation. The peptides conformational properties correlated well with their functional behavior. Thus, P1-30 exhibited much higher hemolytic activity than P11-30. In addition, P11-30 was able to block the toxin's hemolytic activity. The size of pores formed in red blood cells by P1-30 was estimated by measuring the permeability to PEGs of different molecular mass. The pore radius (0.95 +/- 0.01 nm) was very similar to that of the pore formed by the toxin. The results demonstrate that the synthetic peptide P1-30 is a good model of St II conformation and function and emphasize the contribution of the toxin's N-terminal region, and, in particular, the hydrophobic residues 1-10 to pore formation.

Efficacy of furunculosis vaccines in turbot, Scophthalmus maximus (L.): evaluation of immersion, oral and injection delivery

The commercial furunculosis vaccine Aquavac Furovac 5 and an autogenous vaccine, based on the challenge strain, induced immune protection in turbot, Scophthalmus maximus (L.), as shown in challenge tests 120 days post-immunization by injection (relative percentage of survival, RPS = 72-99%). This protective effect lasted for at least 6 months post-immunization at appreciable levels (RPS = 50-52%). Neither the autogenous vaccine nor the commercial vaccine was able to induce significant levels of protection against Aeromonas salmonicida in turbot when administered by immersion. Antibody levels were high or moderate in fish vaccinated by injection with the different vaccines and very low in fish vaccinated by immersion. The field results show that delivering an oral boost after the primary vaccination by injection did not enhance protection of turbot against furunculosis and that water-based (autogenous vaccine) and oil adjuvanted (Alpha Ject 1200) vaccines administered by injection conferred similar levels of protection (RPS > 80%) in turbot.

Differential regulation of gonadotropins and glycoprotein hormone alpha-subunit by IGF-I in anterior pituitary cells from male rats

IGF-I has been demonstrated to stimulate basal and GnRH-induced gonadotropin release. IGF-I also elicites alpha-subunit secretion in human pituitary tumor cells. The aims of this study were to evaluate both the effect of IGF-I on gonadotropin LH-beta and FSH-beta mRNA levels and glycoprotein alpha-subunit gene expression in cultured rat anterior pituitary cells. The exposure of pituitary cells to recombinant human IGF-I (rhlGF-I; 2 microg/ml) for 72 h markedly stimulated basal LH and FSH release whereas their mRNA levels remained unmodified. IGF-I elicited a-subunit release from pituitary cells (p < 0.01) and augmented its mRNA levels. Exposure to IGF-I consistently reduced GH release from pituitary cells. This study shows that the gonadotropin-releasing effects of IGF-I are not paralleled by changes in their mRNAs whereas IGF-I stimulates not only alpha-subunit release but also its mRNA levels. This study provides the first observation of alpha-subunit regulation by IGF-I in normal pituitary cells, where a differential regulation between release and synthesis for gonadotropin a-and 1-subunits is also shown.

Construction of an immunotoxin with the pore forming protein StI and ior C5, a monoclonal antibody against a colon cancer cell line

Sticholysin I (StI), a potent cytolysin isolated from the sea anemone Stichodactyla helianthus, was linked to the monoclonal antibody (mAb) ior C5. StI acts by forming hydrophilic pores in the membrane of the attacked cells leading to osmotic lysis. ior C5 is a murine IgG1, which recognizes the tumor associated antigen (TAA) ior C2. The cytolysin and the mAb were coupled by using the heterobifunctional cross-linking reagent sulfosuccinimidyl 4-(N-maleimidomethyl)-cyclohexane-1-carboxylate (SMCC). Two hybrid molecules composed by one ior C5 and one or two StI molecules were obtained (named conjugated I and II, respectively). The purified conjugates were evaluated by a binding affinity assay against an ior C2-positive colon cancer cell line (SW948). Both molecules were able to recognize the antigen (Ag) in the same way that unconjugated ior C5 does. The activity of both conjugates against human erythrocytes and SW948 cells was assessed. They lost most of their hemolytic activity but their residual activity was very similar. Nevertheless, when their cytotoxicity was studied on the SW948 cell line, only conjugate II killed efficiently the cells, indicating a specific mAb-Ag interaction. In this chimeric molecule the ratio between the cytotoxic and the hemolytic activity was larger than that of the free cytolysin. This fact indicates an increase of the specificity of the toxic effect toward the SW948 cell line and consequently an increase of the difference between its hemolytic and cytotoxic doses. The results herein support the feasibility of directing StI to the surface of cancer cells expressing ior C2 Ag via the mAb ior C5.

A neural network approach to evaluate fold recognition results

Fold recognition techniques assist the exploration of protein structures, and web-based servers are part of the standard set of tools used in the analysis of biochemical problems. Despite their success, current methods are only able to predict the correct fold in a relatively small number of cases. We propose an approach that improves the selection of correct folds from among the results of two methods implemented as web servers (SAMT99 and 3DPSSM). Our approach is based on the training of a system of neural networks with models generated by the servers and a set of associated characteristics such as the quality of the sequence-structure alignment, distribution of sequence features (sequence-conserved positions and apolar residues), and compactness of the resulting models. Our results show that it is possible to detect adequate folds to model 80% of the sequences with a high level of confidence. The improvements achieved by taking into account sequence characteristics open the door to future improvements by directly including such factors in the step of model generation. This approach has been implemented as an automatic system LIBELLULA, available as a public web server at http://www.pdg.cnb.uam.es/servers/libellula.html.

Effects of sodium dodecyl sulfate on the conformation and hemolytic activity of St I and St II, two isotoxins purified from Stichodactyla helianthus

The effect of sodium dodecyl sulfate (SDS) upon the conformation and hemolytic activity of St I and St II strongly depends on its concentration. At relatively low surfactant concentrations (ca. 0.5-5mM range) the surfactant leads to the formation of aggregates, as suggested by the turbidity observed even at relatively low (micromolar range) protein concentrations. In this surfactant range, the proteins show an increase in intrinsic fluorescence intensity and reduced quenching by acrylamide, with an almost total loss of its hemolytic activity. At higher surfactant concentrations the protein adducts disaggregates. This produces a decrease in fluorescence intensity, increase in quenching efficiency by acrylamide, loss of the native tertiary conformation (as reported by the near UV-CD spectra), and increase in alpha-helix content (as evidenced by the far UV-CD spectra). However, and in spite of these substantial changes, the toxins partially recover their hemolytic activity. The reasons for this recovering of the activity at high surfactant concentrations is discussed.

CAFASP2: the second critical assessment of fully automated structure prediction methods

The results of the second Critical Assessment of Fully Automated Structure Prediction (CAFASP2) are presented. The goals of CAFASP are to (i) assess the performance of fully automatic web servers for structure prediction, by using the same blind prediction targets as those used at CASP4, (ii) inform the community of users about the capabilities of the servers, (iii) allow human groups participating in CASP to use and analyze the results of the servers while preparing their nonautomated predictions for CASP, and (iv) compare the performance of the automated servers to that of the human-expert groups of CASP. More than 30 servers from around the world participated in CAFASP2, covering all categories of structure prediction. The category with the largest participation was fold recognition, where 24 CAFASP servers filed predictions along with 103 other CASP human groups. The CAFASP evaluation indicated that it is difficult to establish an exact ranking of the servers because the number of prediction targets was relatively small and the differences among many servers were also small. However, roughly a group of five "best" fold recognition servers could be identified. The CASP evaluation identified the same group of top servers albeit with a slightly different relative order. Both evaluations ranked a semiautomated method named CAFASP-CONSENSUS, that filed predictions using the CAFASP results of the servers, above any of the individual servers. Although the predictions of the CAFASP servers were available to human CASP predictors before the CASP submission deadline, the CASP assessment identified only 11 human groups that performed better than the best server. Furthermore, about one fourth of the top 30 performing groups corresponded to automated servers. At least half of the top 11 groups corresponded to human groups that also had a server in CAFASP or to human groups that used the CAFASP results to prepare their predictions. In particular, the CAFASP-CONSENSUS group was ranked 7. This shows that the automated predictions of the servers can be very helpful to human predictors. We conclude that as servers continue to improve, they will become increasingly important in any prediction process, especially when dealing with genome-scale prediction tasks. We expect that in the near future, the performance difference between humans and machines will continue to narrow and that fully automated structure prediction will become an effective companion and complement to experimental structural genomics.

Identity between cytolysins purified from two morphos of the Caribbean sea anemone Stichodactyla helianthus

Stichodactyla helianthus is a sea anemone relatively abundant along Cuban coasts appearing in two morphos with different colors in their tentacles: green or brownish, probably due to their association with algal symbionts. Traditionally, the brownish morpho has been used as a source of sticholysins I and II, the most characterized cytolysins from this anemone, but the green morpho is the most abundant along the western coasts of Havana. The present work is aimed to establish if the cytolysins purified from the green morpho (StIg and StIIg) are similar to those purified from brownish anemones (StI and StII). Following the same chromatographic procedure used to purify the toxins from morphos, the electrophoretic mobilities, amino acid compositions, amino terminal sequences and molecular masses were practically identical between analogal cytolysins. In conclusion, homologous sticholysins purified from the green and brownish variants of Stichodactyla helianthus are the same molecular entities.

EVA: continuous automatic evaluation of protein structure prediction servers

Evaluation of protein structure prediction methods is difficult and time-consuming. Here, we describe EVA, a web server for assessing protein structure prediction methods, in an automated, continuous and large-scale fashion. Currently, EVA evaluates the performance of a variety of prediction methods available through the internet. Every week, the sequences of the latest experimentally determined protein structures are sent to prediction servers, results are collected, performance is evaluated, and a summary is published on the web. EVA has so far collected data for more than 3000 protein chains. These results may provide valuable insight to both developers and users of prediction methods.

AVAILABILITY

http://cubic.bioc.columbia.edu/eva.

CONTACT

eva@cubic.bioc.columbia.edu

Threading structural model of the manganese-stabilizing protein PsbO reveals presence of two possible beta-sandwich domains

The manganese-stabilizing protein (PsbO) is an essential component of photosystem II (PSII) and is present in all oxyphotosynthetic organisms. PsbO allows correct water splitting and oxygen evolution by stabilizing the reactions driven by the manganese cluster. Despite its important role, its structure and detailed functional mechanism are still unknown. In this article we propose a structural model based on fold recognition and molecular modeling. This model has additional support from a study of the distribution of characteristics of the PsbO sequence family, such as the distribution of conserved, apolar, tree-determinants, and correlated positions. Our threading results consistently showed PsbO as an all-beta (beta) protein, with two homologous beta domains of approximately 120 amino acids linked by a flexible Proline-Glycine-Glycine (PGG) motif. These features are compatible with a general elongated and flexible architecture, in which the two domains form a sandwich-type structure with Greek key topology. The first domain is predicted to include 8 to 9 beta-strands, the second domain 6 to 7 beta-strands. An Ig-like beta-sandwich structure was selected as a template to build the 3-D model. The second domain has, between the strands, long-loops rich in Pro and Gly that are difficult to model. One of these long loops includes a highly conserved region (between P148 and P174) and a short alpha-helix (between E181 and N188)). These regions are characteristic parts of PsbO and show that the second domain is not so similar to the template. Overall, the model was able to account for much of the experimental data reported by several authors, and it would allow the detection of key residues and regions that are proposed in this article as essential for the structure and function of PsbO.

Properties of St I and St II, two isotoxins isolated from Stichodactyla helianthus: a comparison

Sticholysins I and II are two highly hemolytic polypeptides purified from the Caribbean Sea anemone Stichodactyla helianthus. Their high sequence homology (93%) indicates that they correspond to isoforms of the same hemolysin. The spectroscopic measurements show a close similarity in the secondary structure content, conformation and stability of both toxins. Exposure of the toxins to high pHs (>11), a free radical source (AAPH), urea or temperature produce permanent changes in the toxin that lead to a significant loss of HA. It is significant to note that this loss of hemolytic activity occurs when other indicators, probably with the only exception of near-UV CD spectra, barely detect changes in the protein structure. This emphasizes the sensitivity of the protein function to changes in the macromolecule conformation. The most noticeable difference between both toxins is the considerably higher activity of St II, both measured in terms of erythrocyte internal K(+) exit or hemolysis; which is related to enthalpic factors. This difference is not due to an incomplete association of St I to the membrane. We consider then that the different pore forming capacity of both toxins in erythrocytes can be explained in terms of the difference in charge of the N-terminal fragment, than can considerably reduce the St I insertion rate in the membrane probably due to the negatively charged outer leaflet of the red blood cell, without a significant reduction of its capacity to bind to the cell membrane. This electrostatic effect, together with a slightly more relaxed structure in St II, could explain the higher pore forming capacity of St II in the red blood cell membrane.

Similarity of phylogenetic trees as indicator of protein-protein interaction

Deciphering the network of protein interactions that underlines cellular operations has become one of the main tasks of proteomics and computational biology. Recently, a set of bioinformatics approaches has emerged for the prediction of possible interactions by combining sequence and genomic information. Even though the initial results are very promising, the current methods are still far from perfect. We propose here a new way of discovering possible protein-protein interactions based on the comparison of the evolutionary distances between the sequences of the associated protein families, an idea based on previous observations of correspondence between the phylogenetic trees of associated proteins in systems such as ligands and receptors. Here, we extend the approach to different test sets, including the statistical evaluation of their capacity to predict protein interactions. To demonstrate the possibilities of the system to perform large-scale predictions of interactions, we present the application to a collection of more than 67 000 pairs of E.coli proteins, of which 2742 are predicted to correspond to interacting proteins.

Effects of lipid composition on membrane permeabilization by sticholysin I and II, two cytolysins of the sea anemone Stichodactyla helianthus

Sticholysin I and II (St I and St II), two basic cytolysins purified from the Caribbean sea anemone Stichodactyla helianthus, efficiently permeabilize lipid vesicles by forming pores in their membranes. A general characteristic of these toxins is their preference for membranes containing sphingomyelin (SM). As a consequence, vesicles formed by equimolar mixtures of SM with phosphatidylcholine (PC) are very good targets for St I and II. To better characterize the lipid dependence of the cytolysin-membrane interaction, we have now evaluated the effect of including different lipids in the composition of the vesicles. We observed that at low doses of either St I or St II vesicles composed of SM and phosphatidic acid (PA) were permeabilized faster and to a higher extent than vesicles of PC and SM. As in the case of PC/SM mixtures, permeabilization was optimal when the molar ratio of PA/SM was ~1. The preference for membranes containing PA was confirmed by inhibition experiments in which the hemolytic activity of St I was diminished by pre-incubation with vesicles of different composition. The inclusion of even small proportions of PA into PC/SM LUVs led to a marked increase in calcein release caused by both St I and St II, reaching maximal effect at ~5 mol % of PA. Inclusion of other negatively charged lipids (phosphatidylserine (PS), phosphatidylglycerol (PG), phosphatidylinositol (PI), or cardiolipin (CL)), all at 5 mol %, also elicited an increase in calcein release, the potency being in the order CL approximately PA >> PG approximately PI approximately PS. However, some boosting effect was also obtained, including the zwitterionic lipid phosphatidylethanolamine (PE) or even, albeit to a lesser extent, the positively charged lipid stearylamine (SA). This indicated that the effect was not mediated by electrostatic interactions between the cytolysin and the negative surface of the vesicles. In fact, increasing the ionic strength of the medium had only a small inhibitory effect on the interaction, but this was actually larger with uncharged vesicles than with negatively charged vesicles. A study of the fluidity of the different vesicles, probed by the environment-sensitive fluorescent dye diphenylhexatriene (DPH), showed that toxin activity was also not correlated to the average membrane fluidity. It is suggested that the insertion of the toxin channel could imply the formation in the bilayer of a nonlamellar structure, a toroidal lipid pore. In this case, the presence of lipids favoring a nonlamellar phase, in particular PA and CL, strong inducers of negative curvature in the bilayer, could help in the formation of the pore. This possibility is confirmed by the fact that the formation of toxin pores strongly promotes the rate of transbilayer movement of lipid molecules, which indicates local disruption of the lamellar structure.

Purification and characterization of two hemolysins from Stichodactyla helianthus

Two hemolysins, Sticholysin I (St I) and Sticholysin II (St II) were purified from the sea anemone Stichodactyla helianthus combining gel filtration and ion exchange chromatography. The amino acid composition of both cytolysins was determined revealing a high proportion of glycine, lysine, tyrosine and non-polar amino acids (alanine, leucine and valine). Cysteine was not found in either polypeptide. Molecular masses of St I and St II were 19401 and 19290 Da, respectively. N-terminal sequence analysis of St I and St II showed a high homology between them suggesting they are isoforms of the same cytolysin. Compared with other sea anemone cytolysins, St I and St II contain a 22 amino acid insertion fragment also present in Eq T II/Tn C and probably in CaT I and Hm T and absent in C III, the major hemolysin previously reported in this anemone.

Mechanisms of reduced body growth in the pubertal feminized male rat: unbalanced estrogen and androgen action on the somatotropic axis

It is well known that the sex difference in body growth at puberty is modulated by a complex interplay between sex steroids and somatotropic axis; however, the exact role played by sex steroids remains a matter of controversy. The aim of this study was to assess the mechanisms by which sex steroids regulate body growth during pubertal development. Flutamide, a non-steroid-blocking androgen receptor, was subcutaneously administered to 30-d-old male Wistar rats for 4 wk. The blockade of the androgen receptor led to a marked elevation in serum testosterone and an increment in serum estradiol. Flutamide administration decreased body weight gain, serum IGF-I levels, hepatic IGF-I mRNA, and GH receptor mRNA content. There were no significant changes in serum GH concentration, pituitary GH reserve, and pituitary GH mRNA content. Flutamide lowered hypothalamic somatostatin mRNA content and augmented hypothalamic immunoreactive somatostatin stores, but did not alter hypothalamic immunoreactive GH-releasing factor stores. Our findings indicate that during pubertal development of the male rat, the imbalance between androgen and estrogen actions determines an abnormal somatic growth, which is at least partly exerted through the peripheral or hepatic modification of the somatotropic axis that occurs under the high or exclusive action of estrogens. Potential implication of coincident sex-specific regulated mode of pulsatile GH secretion cannot be excluded from this random serum GH sample study.

A platform for integrating threading results with protein family analyses

We have developed a package for the interactive visualization of results from different threading programs. Additionally, we have integrated relevant information about protein sequence, function, evolution, and structure into the interface.

Decreased plasma endothelin-1 levels in asymptomatic type I diabetic patients with regional cerebral hypoperfusion assessed by Spect

The prevalence of stroke is increased in diabetic patients. The vasoconstrictor peptide endothelin-1 (ET-1) has been implicated in the development of cerebral vasospasm after stroke but its role in the physiological regulation of cerebral blood flow (CBF) is not well known. Our aim was to assess the relationship between CBF and plasma ET-1 levels in type I diabetic patients. Regional CBF was assessed semi-quantitatively by 99Tc(m)-hexamethylpropylene-amine-oxime (99Tc(m)-HMPAO) single photon emission computed tomography (SPECT) in 50 cerebral "regions of interest" (ROIs) of 19 type I diabetic patients without clinical evidence of cerebral disease, and 10 healthy control subjects. In both groups, plasma ET-1 levels were measured. Results showed that type I diabetic patients had significantly more hypoperfusion ROIs than control subjects. While up to 68.4% of the type I diabetic patients showed 3 or more hypoperfusion ROIs, only 10% of the control subjects did. Plasma ET-1 levels were lower in the type I diabetes subgroup with 3 or more hypoperfusion ROIs than in the type I diabetes subgroup with less than 3 hypoperfusion ROIs and in the control group. Moreover, an inverse correlation between the number of hypoperfusion ROIs and plasma ET-1 levels (r = 0.47, p = 0.04) was found in the type I diabetes group. It is concluded that plasma ET-1 is decreased in type I diabetic patients with subclinical abnormalities of regional CBF assessed by cerebral SPECT. This fact may reflect a compensatory response to the reduction of the brain perfusion in order to prevent ischemic events in these patients.

Patients with poor preoperative ejection fraction have a higher plasma response of adrenomedullin in response to open heart surgery

BACKGROUND

Adrenomedullin (AM) is a potent vasodilator peptide. Plasma AM levels are increased in heart diseases and in sepsis. Heart surgery under cardiopulmonary bypass (CPB) induces a systemic inflammatory response.

METHODS

We measured plasma AM, cAMP (the second messenger of AM), C-reactive protein (CRP) and haemodynamic parameters in 29 patients undergoing elective open heart surgery, before, during and after anaesthesia and CPB as well as on the first morning after surgery.

RESULTS

Basal AM levels were higher than normal and correlated with systolic pulmonary pressure and pulmonary capillary pressure, but not with other haemodynamic parameters. AM increased during CPB and remained elevated 24 h after the start of surgery. Plasma cAMP increased only at the end of CPB. CRP was increased only in the last sample. At the end of CPB and at the end of surgery AM levels were higher in patients with basal ejection fraction<40% compared with those with ejection fraction >60% [456+/-386 vs 252+/-343 (P<0.03) and 832+/-781 vs 391+/-356 pg/ml (P<0.05), respectively].

CONCLUSION

We conclude that AM, as inflammation-related cytokines, increases during and after CPB, that cAMP response is unrelated to AM and that AM response is higher in those patients with worse basal ejection fraction.

Regulation of gonadal and somatotropic axis by chronic intraventricular infusion of insulin-like growth factor 1 antibody at the initiation of puberty in male rats

There has been increasing experimental evidence to suggest that insulin-like growth factor 1 (IGF-I) may be one of the essential regulators in the reproductive system of the rat. IGF-I is synthesized in the hypothalamus and IGF-I immunoreactivity increases during puberty. Consequently we hypothesized that centrally located IGF-I might contribute to the initiation of puberty. Centrally located IGF-I was immunoneutralized to assess this hypothesis. Male Wistar rats, 28 days old, were infused intracerebroventricularly with specific purified IgGs from rabbit IGF-I antiserum (IGF-I-Ab). The intracerebroventricular administration of IGF-I-Ab resulted in a reduction in testicular weight and consequently in delayed pubertal development. There was also a reduction in serum testosterone, pituitary immunoreactive (IR) luteinizing hormone (LH) and serum IR follicle-stimulating hormone (FSH). The accumulation of betaLH mRNA was not modified, whereas betaFSH mRNA was increased. An increment in the serum growth hormone (GH) levels was also observed. There were no significant alterations in hypothalamic IR growth hormone releasing factor content, although IR somatostatin (SRIH) content was increased by IGF-I-Ab. The body weight gain remained unaltered. As a whole, our study suggests that centrally located IGF-I influences pubertal development, production and release of gonadotropins and supports the finding that endogenous centrally located IGF-I plays a role at the initiation of puberty in the male rat. It also gives support to the physiological role of centrally located IGF-I in the release of GH mediated by hypothalamic SRIH at the initiation of puberty.

Prospective randomized study comparing the long-acting gonadotropin-releasing hormone agonist triptorelin, flutamide, and cyproterone acetate, used in combination with an oral contraceptive, in the treatment of hirsutism

OBJECTIVE

To compare triptorelin, cyproterone acetate (CPA), and flutamide, in combination with an oral contraceptive, in the treatment of hirsutism.

DESIGN

Prospective randomized study.

SETTING(S)

Tertiary care hospital.

PATIENT(S)

Thirty-nine hirsute women with idiopathic or functional ovarian hyperandrogenism.

INTERVENTION(S)

Patients were randomly assigned to receive triptorelin (3.75 mg IM every 28 days), CPA (100 mg/d orally on days 1-10 of the menstrual cycle), or flutamide (250 mg orally twice daily). All the patients also received a triphasic oral contraceptive.

MAIN OUTCOME MEASURE(S)

Before and after 3 and 9 months of treatment, the Ferriman-Gallwey score, hepatic function, and gonadal and adrenal steroid profiles were evaluated.

RESULTS

Thirty-three patients completed the 9-month study period. The Ferriman-Gallwey score decreased in all the groups. In the patients treated with CPA or flutamide, a decrease in the hirsutism score was noted as soon as after 3 months of treatment. This decrease was more pronounced after 9 months of treatment, especially in the patients who received flutamide, who had lower hirsutism scores compared with the other treatment groups. None of the patients had abnormal liver function test results. There was a mild increase in serum lipid concentrations, mostly in the group treated with triptorelin.

CONCLUSION(S)

Triptorelin, CPA, and flutamide are effective drugs for the treatment of hirsutism. Flutamide results in a greater reduction in the hirsutism score, but CPA also offers satisfactory results at a much lower cost. Triptorelin has no advantages over flutamide and CPA, and is the most expensive of the three drugs tested.

Direct action of serotonin on prolactin, growth hormone, corticotropin and luteinizing hormone release in cocultures of anterior and posterior pituitary lobes: autocrine and/or paracrine action of vasoactive intestinal peptide

There is extensive evidence that serotonin (5-HT) is implicated in the neuroendocrine control regulating the secretion of several anterior pituitary hormones. It has also been reported that the posterior pituitary is necessary for prolactin (PRL) response to 5-HT as well as to suckling, in which 5-HT implication has been demonstrated. As we have previously shown that vasoactive intestinal peptide (VIP) mediates through an autocrine or paracrine action the PRL release induced by insulin-like growth factor I, thyrotropin-releasing hormone (TRH) and dopamine withdrawal, the aim of the present work was to determine whether 5-HT has a direct action on pituitary secretion and to study the possible role of pituitary VIP in this situation. Cells from the anterior pituitary lobe (AP) were cultured either alone or together with cells from the posterior pituitary lobe (PP). As melanotropes from PP express glucocorticoid receptors in vitro, both AP cultures and cocultures of AP/PP cells were incubated in the presence or absence of corticosterone (0.1 microg/ml), thus designing four experimental conditions. Then both AP and mixed cultures were incubated with 5-HT (100 nM) for 20, 45 and 180. The release of PRL, growth hormone (GH), corticotropin (ACTH) and luteinizing hormone (LH) was stimulated by 5-HT, but only in cocultures of AP/PP cells preincubated with corticosterone, whereas follicle-stimulating hormone and thyroid-stimulating hormone release was not modified. As AP cultures did not show any response to 5-HT, both in the presence or absence of corticosterone, and as melanotropes are the main cellular type present in the PP cultures, we studied the response of alpha-melanocyte-stimulating hormone (alphaMSH) to 5-HT in PP cells cultured with or without corticosterone. Serotonin did not modify alphaMSH release either in the absence or the presence of corticosterone. VIP release was also stimulated by 5-HT in the cocultures, and the time response profile was only similar to that of PRL. In order to study whether pituitary VIP is implicated in 5-HT action, cocultures preincubated with corticosterone were incubated in the presence of 5-HT, a VIP-receptor antagonist (VIP-At) or simultaneously with 5-HT plus VIP-At. PRL response to 5-HT was abolished by the simultaneous presence of VIP-At, whereas GH, ACTH and LH response remained unchanged. These data demostrate that: (1) 5-HT stimulates the secretion of PRL, GH, ACTH, LH and VIP acting directly at pituitary level on PP, probably by releasing an unidentified mediator from melanotropes; (2) glucocorticoids make the response of AP cells to 5-HT possible due to the presence of PP cells in the coculture; (3) PRL response to 5-HT is mediated through an autocrine and/or paracrine action of VIP.

The role of ionic strength on the enhancement of the hemolytic activity of sticholysin I, a cytolysin from Stichodactyla helianthus

Sticholysin I (St I) is a potent cytolytic polypeptide purified from the Caribbean sea anemone Stichodactyla helianthus. The hemolytic activity of sticholysin is potentiated by its preincubation at high ionic strengths. In the present work the mechanism of the potentiating action of the medium ionic strength on the toxin hemolytic capacity is investigated. It is suggested that preincubation with high saline concentration induces a transition of St I to a more relaxed conformation that facilitates the lytic process.

Correlated mutations contain information about protein-protein interaction

Many proteins have evolved to form specific molecular complexes and the specificity of this interaction is essential for their function. The network of the necessary inter-residue contacts must consequently constrain the protein sequences to some extent. In other words, the sequence of an interacting protein must reflect the consequence of this process of adaptation. It is reasonable to assume that the sequence changes accumulated during the evolution of one of the interacting proteins must be compensated by changes in the other. Here we apply a method for detecting correlated changes in multiple sequence alignments to a set of interacting protein domains and show that positions where changes occur in a correlated fashion in the two interacting molecules tend to be close to the protein-protein interfaces. This leads to the possibility of developing a method for predicting contacting pairs of residues from the sequence alone. Such a method would not need the knowledge of the structure of the interacting proteins, and hence would be both radically different and more widely applicable than traditional docking methods. We indeed demonstrate here that the information about correlated sequence changes is sufficient to single out the right inter-domain docking solution amongst many wrong alternatives of two-domain proteins. The same approach is also used here in one case (haemoglobin) where we attempt to predict the interface of two different proteins rather than two protein domains. Finally, we report here a prediction about the inter-domain contact regions of the heat- shock protein Hsc70 based only on sequence information.

Growth hormone induces somatostatin and insulin-like growth factor I gene expression in the cerebral hemispheres of aging rats

The neuropeptide somatostatin (SS) plays a role as a modulator of cognitive functions and as a potential tropic factor in the central nervous system. A reduction in SS levels has been demonstrated in the aging brain and in dementia. In addition, insulin-like growth factor I (IGF-I) acts as a paracrine factor in multiple GH actions and is also found in the cerebral hemispheres, where it exerts neurotropic effects. We used aging rats as an in vivo model of GH deficiency to study the possible participation of exogenous GH in the modulation of the cerebral hemispheric SS and IGF-I. Two sets of experiments were carried out. In the first set, the age-related patterns of GH, IGF-I, and SS in the serum, pituitary, and cerebral hemispheres were established. In the second experimental set, 90-day-old (adult) and 2-yr-old (aging) male rats received recombinant human GH (200 micrograms/ sc-day) or vehicle for 7 consecutive days. The serum levels of rat GH and IGF-I as well as pituitary GH messenger RNA decreased in 2-yr-old rats compared with those in adult rats. After GH treatment, pituitary GH messenger RNA levels decreased markedly in the 90-day-old and 2-yr-old rats. Serum immunoreactive GH decreased in the adult animals, whereas it remained unaffected in the aging ones, whereas serum IGF-I levels were not altered by GH treatment in either group. Immunoreactive levels and messenger RNA of both SS and IGF-I were low in the cerebral hemispheres of aging rats, but were restored to the levels found in adult rats after GH treatment. As treatment did not induce changes in the serum IGF-I levels, these results provide evidence of a stimulatory action of peripherally administered GH on the regulation of SS and IGF-I genes in the aging rat in the central nervous system. These data also show a new target action for GH and could provide a molecular basis for the improvement of some symptoms of GH deficiency that occurs after recombinant human GH treatment.