Thais savignyi tissue extract: bioactivity, chemical composition, and molecular docking

CONTEXT

Thais savignyi Deshayes (Muricidae) is widely distributed in the Red Sea. Its abundance and the history of Muricidae in traditional medicine make it a tempting target for investigation.

OBJECTIVE

To investigate the chemical profile and biological activities of T. savignyi tissue extracts.

MATERIALS AND METHODS

Methanol, ethanol, acetone, and ethyl acetate extracts from T. savignyi tissue were compared in their antioxidant by total antioxidant capacity, DPPH free radical scavenging, and total phenolic content. In addition, the antimicrobial, and antibiofilm properties (at 250 µg/mL) of the extracts were tested against Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris, Klebsiella pneumoniae, Staphylococcus aureus, and Candida albicans. The antioxidant extract with greatest activity was assessed for cytotoxicity (range 0.4-100 µg/mL) against 3 human cancer cell lines (UO-31, A549 and A431), and its chemical composition was investigated using GC-MS. Moreover, docking simulation was performed to predict its constituents' binding modes/scores to the active sites of thymidylate kinase.

RESULTS

The ethyl acetate extract (Ts-EtOAc) showed the highest total antioxidant capacity (551.33 mg AAE/g dry weight), total phenolics (254.46 mg GAE/g dry weight), and DPPH scavenging (IC₅₀= 24.0 µg/mL). Ts-EtOAc exhibited strong antibacterial (MIC: 3.9 µg/mL against K. pneumoniae), antibiofilm (MIC: 7.81 µg/mL against S. aureus), and antifungal (MIC: 3.9 µg/mL against C. albicans) activities and considerable cytotoxicity against cancer cells (UO-31: IC₅₀= 19.96 ± 0.93, A549: IC₅₀= 25.04 ± 1.15 μg/mL). GC-MS identified multiple bioactive metabolites in Ts-EtOAc extract belonging to miscellaneous chemical classes. Molecular docking studies revealed that the constituents of Ts-EtOAc have antibacterial potential.

DISCUSSION AND CONCLUSIONS

T. savignyi extract has considerable antimicrobial and cytotoxic activities. Further studies are needed to isolate the active constituents of this snail for comprehensive drug discovery tests.

Characterization of the bacterial community of the chemically defended Hawaiian sacoglossan Elysia rufescens

Sacoglossans are characterized by the ability to sequester functional chloroplasts from their algal diet through a process called kleptoplasty, enabling them to photosynthesize. The bacterial diversity associated with sacoglossans is not well understood. In this study, we coupled traditional cultivation-based methods with 454 pyrosequencing to examine the bacterial communities of the chemically defended Hawaiian sacoglossan Elysia rufescens and its secreted mucus. E. rufescens contains a defense molecule, kahalalide F, that is possibly of bacterial origin and is of interest because of its antifungal and anticancer properties. Our results showed that there is a diverse bacterial assemblage associated with E. rufescens and its mucus, with secreted mucus harboring higher bacterial richness than entire-E. rufescens samples. The most-abundant bacterial groups affiliated with E. rufescens and its mucus are Mycoplasma spp. and Vibrio spp., respectively. Our analyses revealed that the Vibrio spp. that were highly represented in the cultivable assemblage were also abundant in the culture-independent community. Epifluorescence microscopy and matrix-assisted laser desorption-ionization mass spectrometry (MALDI-MS) were utilized to detect the chemical defense molecule kahalalide F on a longitudinal section of the sacoglossan.

Glycosylation of conotoxins

Conotoxins are small peptides present in the venom of cone snails. The snail uses this venom to paralyze and capture prey. The constituent conopeptides display a high level of chemical diversity and are of particular interest for scientists as tools employed in neurological studies and for drug development, because they target with exquisite specificity membrane receptors, transporters, and various ion channels in the nervous system. However, these peptides are known to contain a high frequency and variability of post-translational modifications-including sometimes O-glycosylation-which are of importance for biological activity. The potential application of specific conotoxins as neuropharmalogical agents and chemical probes requires a full characterization of the relevant peptides, including the structure of the carbohydrate part. In this review, the currently existing knowledge of O-glycosylation of conotoxins is described.

Molluscan biological and chemical diversity: secondary metabolites and medicinal resources produced by marine molluscs

The phylum Mollusca represents an enormous diversity of species with eight distinct classes. This review provides a taxonomic breakdown of the published research on marine molluscan natural products and the medicinal products currently derived from molluscs, in order to identify priority targets and strategies for future research. Some marine gastropods and bivalves have been of great interest to natural products chemists, yielding a diversity of chemical classes and several drug leads currently in clinical trials. Molluscs also feature prominently in a broad range of traditional natural medicines, although the active ingredients in the taxa involved are typically unknown. Overall secondary metabolites have only been investigated from a tiny proportion (<1%) of molluscan species. At the class level, the number of species subject to chemical studies mirrors species richness and our relative knowledge of the biology of different taxa. The majority of molluscan natural products research is focused within one of the major groups of gastropods, the opisthobranchs (a subgroup of Heterobranchia), which are primarily comprised of soft-bodied marine molluscs. Conversely, most molluscan medicines are derived from shelled gastropods and bivalves. The complete disregard for several minor classes of molluscs is unjustified based on their evolutionary history and unique life styles, which may have led to novel pathways for secondary metabolism. The Polyplacophora, in particular, have been identified as worthy of future investigation given their use in traditional South African medicines and their abundance in littoral ecosystems. As bioactive compounds are not always constitutively expressed in molluscs, future research should be targeted towards biosynthetic organs and inducible defence reactions for specific medicinal applications. Given the lack of an acquired immune system, the use of bioactive secondary metabolites is likely to be ubiquitous throughout the Mollusca and broadening the search field may uncover interesting novel chemistry.

Structure-function relationship of conotoxin lt14a, a potential analgesic with low cytotoxicity

A novel conotoxin lt14a containing 13 amino acid residues with an amidated C-terminus derived from Conus litteratus, belongs to C-C-C-C cysteine pattern. As the smallest peptide of conotoxin framework 14, lt14a could inhibit nicotinic acetylcholine receptor and suppress pain. To elucidate structure-function relationship, we determine the solution structure by NMR and find that lt14a comprises a short duple β-strand region and β-turn motif. An analog [K7A]-lt14a of Ala substitution for Lys in position 7 is designed. Interestingly, [K7A]-lt14a exhibits higher activity than lt14a as long-lasting analgesic in the hotplate pain model in mice. Additionally, MTT assay reveals that the two peptides have low toxicity to human cells. The studies suggest that positively charged residue may not be involved in the blocking mechanism. However, due to the Ala substitution, hydrophobic residues' patch expansion strengthens the binding ability. A hypothesis is given that in conotoxin lt14a, hydrophobic residues rather than charged residues play a key role during target binding.

New conopeptides of the D-superfamily selectively inhibiting neuronal nicotinic acetylcholine receptors

The venom of cone snails (Conus spp.) is a rich source of peptides exhibiting a wide variety of biological activities. Several of these conopeptides are neuronal nicotinic acetylcholine receptor (nAChR) antagonists and belong to the A-, M-, S-, C and the recently described D-superfamily (alphaD-conopeptides). Here we describe the discovery and characterization of two alphaD-conopeptides isolated from the venom of Conus mustelinus and Conus capitaneus. Their primary structure was determined by Edman degradation, MS/MS analysis and by a PCR based approach. These peptides show close structural homology to the alphaD-VxXIIA, -B and -C conopeptides from the venom of Conus vexillum and are dimers (about 11kDa) of similar or identical peptides with 49 amino acid residues and a characteristic arrangement of ten conserved cysteine residues. These novel types of conopeptides specifically block neuronal nAChRs of the alpha7, alpha3beta2 and alpha4beta2 subtypes in nanomolar concentrations. Due to their high affinity, these new ligands may provide a tool to decipher the localisation and function of the various neuronal nAChRs.

Rapid sensitive analysis of cysteine rich peptide venom components

Disulfide-rich peptide venoms from animals such as snakes, spiders, scorpions, and certain marine snails represent one of nature's great diversity libraries of bioactive molecules. The various species of marine cone shells have alone been estimated to produce >50,000 distinct peptide venoms. These peptides have stimulated considerable interest because of their ability to potently alter the function of specific ion channels. To date, only a small fraction of this immense resource has been characterized because of the difficulty in elucidating their primary structures, which range in size between 10 and 80 aa, include up to 5 disulfide bonds, and can contain extensive posttranslational modifications. The extraordinary complexity of crude venoms and the lack of DNA databases for many of the organisms of interest present major analytical challenges. Here, we describe a strategy that uses mass spectrometry for the elucidation of the mature peptide toxin components of crude venom samples. Key to this strategy is our use of electron transfer dissociation (ETD), a mass spectrometric fragmentation technique that can produce sequence information across the entire peptide backbone. However, because ETD only yields comprehensive sequence coverage when the charge state of the precursor peptide ion is sufficiently high and the m/z ratio is low, we combined ETD with a targeted chemical derivatization strategy to increase the charge state of cysteine-containing peptide toxins. Using this strategy, we obtained full sequences for 31 peptide toxins, using just 7% of the crude venom from the venom gland of a single cone snail (Conus textile).

Structural characterization of five post-translationally modified isomorphs of a novel putative delta-conotoxin from the vermivorous snail Conus delessertii from the Mexican Caribbean Sea

A novel peptide, de7b, was isolated from the venom of Conus delessertii, a worm-hunting species collected in the Caribbean Sea off the Yucatan Peninsula. Its primary structure was determined by automated Edman degradation and confirmed by mass spectrometry: it contains 28 amino acids, including six Cys residues. Peptide de7b is the second, O-conotoxin-like peptide isolated from the venom of this species, and it exists in different post-translationally modified isomorphs, some of which contain gamma-carboxy-glutamate (gamma) and/or 4-hydroxy-proline (O) at positions 4, 7, and/or 14. Its primary structure is DCI(P/O)GG(E/gamma)NCDVFR(O/P)YRCCSGYCILLLCA, with molecular masses varying from 3078.6 to 3154.6Da, depending on the number and kind of modified amino acid residues. Peptide de7b shows significant sequence identity with several O-conotoxins purified and biologically characterized from molluscivorous and piscivorous cone snails of the Indo-Pacific region, the tropical Atlantic and Eastern Pacific Oceans, especially with the delta-conotoxins but also with the omega-conotoxins from molluscivorous species, which suggests that it might affect voltage-gated Na(+) or Ca(2+)channels. Peptide de7b has 32% sequence identity with putative gamma-conotoxin de7a, previously characterized from the same species; both peptides contain the same number of amino acid residues and of non-Cys residues between the pairs of consecutive Cys residues. However, these peptides have charge differences at seven positions within the N-terminal half indicating that they might have distinct molecular targets that remain to be identified.

Two new 4-Cys conotoxins (framework 14) of the vermivorous snail Conus austini from the Gulf of Mexico with activity in the central nervous system of mice

As part of continuing studies of the venom components present in Conus austini (syn.: Conus cancellatus), a vermivorous cone snail collected in the western Gulf of Mexico, Mexico, two major peptides, as14a and as14b, were purified and characterized. Their amino acid sequences were determined by automatic Edman sequencing after reduction and alkylation. Their molecular masses, established by matrix-assisted laser desorption ionization time-of-flight mass spectrometry, confirmed the chemical analyses and indicated that as14a and as14b have free C-termini. Each peptide contains 4-Cys residues arranged in a pattern (C-C-C-C, framework 14). The primary structure of as14a is GGVGRCIYNCMNSGGGLNFIQCKTMCY (experimental monoisotopic mass 2883.92Da; calculated monoisotopic mass 2884.20Da), whereas that of as14b is RWDVDQCIYYCLNGVVGYSYTECQTMCT (experimental monoisotopic mass 3308.63Da; calculated monoisotopic mass 3308.34Da). Both purified peptides elicited scratching and grooming activity in mice, and as14b also caused body and rear limb extension and tail curling immediately upon injection. The high sequence similarity of peptide as14a with peptide vil14a from the vermivorous C. villepinii suggests that the former might block K+ channels.

Conorfamide-Sr2, a gamma-carboxyglutamate-containing FMRFamide-related peptide from the venom of Conus spurius with activity in mice and mollusks

A novel peptide, conorfamide-Sr2 (CNF-Sr2), was purified from the venom extract of Conus spurius, collected in the Caribbean Sea off the Yucatan Peninsula. Its primary structure was determined by automated Edman degradation and amino acid analysis, and confirmed by electrospray ionization mass spectrometry. Conorfamide-Sr2 contains 12 amino acids and no Cys residues, and it is only the second FMRFamide-related peptide isolated from a venom. Its primary structure GPM gammaDPLgammaIIRI-nh2, (gamma, gamma-carboxyglutamate; -nh2, amidated C-terminus; calculated monoisotopic mass, 1468.72Da; experimental monoisotopic mass, 1468.70Da) shows two features that are unusual among FMRFamide-related peptides (FaRPs, also known as RFamide peptides), namely the novel presence of gamma-carboxyglutamate, and a rather uncommon C-terminal residue, Ile. CNF-Sr2 exhibits paralytic activity in the limpet Patella opea and causes hyperactivity in the freshwater snail Pomacea paludosa and in the mouse. The sequence similarities of CNF-Sr2 with FaRPs from marine and freshwater mollusks and mice might explain its biological effects in these organisms. It also resembles FaRPs from polychaetes (the prey of C. spurius), which suggests a natural biological role. Based on these similarities, CNF-Sr2 might interact with receptors of these three distinct types of FaRPs, G-protein-coupled receptors, Na+ channels activated by FMRFamide (FaNaCs), and acid-sensing ion channels (ASICs). The biological activities of CNF-Sr2 in mollusks and mice make it a potential tool to study molecular targets in these and other organisms.

I-conotoxins in vermivorous species of the West Atlantic: peptide sr11a from Conus spurius

Peptide sr11a was purified from the venom of Conus spurius, a vermivorous cone snail collected in the Yucatan Channel, in the Western Atlantic. Its primary structure was determined by automatic Edman degradation after reduction and alkylation. Its molecular mass, as determined by MALDI-TOF mass spectrometry (average mass 3650.77 Da), confirmed the chemical data (calculated average mass, 3651.13 Da). The sequence of peptide sr11a (CRTEGMSCgamma gamma NQQCCWRSCCRGECEAPCRFGP&; gamma, gamma-carboxy-Glu; &, amidated C-terminus) shows eight Cys residues arranged in the pattern that defines the I-superfamily of conotoxins. Peptide sr11a contains two gamma-carboxy-Glu residues, a post-translational modification that has been found in other I-conotoxins from species that live in the West Pacific: r11e from the piscivorous Conus radiatus, and kappa-BtX from the vermivorous Conus betulinus. Peptide sr11a is the eighth I-conotoxin isolated from a Conus venom and the first I-conotoxin from a species from the Western Atlantic. Peptide sr11a produced stiffening of body, limbs and tail when injected intracranially into mice.

An O-conotoxin from the vermivorous Conus spurius active on mice and mollusks

Here, we report the purification, amino acid sequence and a preliminary biological characterization of a peptide, sr7a, from the venom of Conus spurius, a vermivorous species collected in the Yucatan Channel, Mexico. The peptide consists of 32 amino acid residues (CLQFGSTCFLGDDDICCSGECFYSGGTFGICS&; &, amidated C-terminus) and contains six cysteines arranged in the pattern (C-C-CC-C-C) that characterizes the O-superfamily of conotoxins. This superfamily includes several pharmacological families (omega-, kappa-, muO-, delta- and gamma-conotoxins) that target Ca(2+), K(+), Na(+) and pacemaker voltage-gated ion channels. Compared with other O-conotoxins that were purified from venoms, this peptide displays sequence similarity with omega-SVIA (from Conus striatus), delta-TxVIA/B (from Conus textile), omega-CVID (from Conus catus) and kappa-PVIIA (from Conus purpurascens). At a dose of 250 pmol, peptide sr7a elicited hyperactivity when injected intracranially into mice and produced paralysis when injected into the pedal muscle of freshwater snails, Pomacea paludosa, but it had no apparent effect after intramuscular injection into the limpet Patella opea or the freshwater fish Lebistes reticulatus.

Identification of a Novel Class of Nicotinic Receptor Antagonists

The venoms of predatory marine snails (Conus spp.) contain diverse mixtures of peptide toxins with high potency and selectivity for a variety of voltage-gated and ligand-gated ion channels. Here we describe the chemical and functional characterization of three novel conotoxins, alphaD-VxXIIA, alphaD-VxXIIB, and alphaD-VxXIIC, purified from the venom of Conus vexillum. Each toxin was observed as an approximately 11-kDa protein by LC/MS, size exclusion chromatography, and SDS-PAGE. After reduction, the peptide sequences were determined by Edman degradation chemistry and tandem MS. Combining the sequence data together with LC/MS and NMR data revealed that in solution these toxins are pseudo-homodimers of paired 47-50-residue peptides. The toxin subunits exhibited a novel arrangement of 10 conserved cystine residues, and additional post-translational modifications contributed heterogeneity to the proteins. Binding assays and two-electrode voltage clamp analyses showed that alphaD-VxXIIA, alphaD-VxXIIB, and alphaD-VxXIIC are potent inhibitors of nicotinic acetylcholine receptors (nAChRs) with selectivity for alpha7 and beta2 containing neuronal nAChR subtypes. These dimeric conotoxins represent a fifth and highly divergent structural class of conotoxins targeting nAChRs.

Screening for post-translational modifications in conotoxins using liquid chromatography/mass spectrometry: an important component of conotoxin discovery

Mass spectrometry has emerged as an important technique for conotoxin analysis due to its capacity for selective, sensitive, information-rich analyses. Using liquid chromatography/mass spectrometry, Conus venom can be fractionated and the peptides surveyed for specific post-translational modifications, indicating those toxin components likely to have an important biological function. With Conus striatus and Conus victoriae venom as models, bromination, carboxylation and glycosylation modifications are identified through characteristics such as isotopic distribution and labile losses observed during mass spectrometric analysis. This modification screening approach enables the identification of a C. victoriae bromo-carboxy-conotoxin, designated vc5c, as a candidate for detailed mass spectrometric analysis. Using a cDNA sequence coupled with liquid chromatography/mass spectrometry and nanoelectrospray ionization-ion trap-mass spectrometry, the sequence of vc5c is determined to be ICCYPNXWCCD, where W is 6-bromotryptophan, X is gamma-carboxy glutamate and C is disulfide-linked cysteine. This represents the ninth T-superfamily (-CC-CC- scaffold) toxin that has been isolated from venom and characterized.

Amino acid sequence and biological activity of a gamma-conotoxin-like peptide from the worm-hunting snail Conus austini

A novel 31-residue toxin, named as7a, was isolated and characterized from the venom of Conus austini, a vermivorous cone snail collected in the western Gulf of Mexico. The complete amino acid sequence, TCKQKGEGCSLDVgammaCCSSSCKPGGPLFDFDC, was determined by automatic Edman sequencing after reduction and alkylation. The sequence shows six Cys residues arranged in the pattern that defines the O-superfamily of conotoxins, and the sequence motif -gammaCCS-, which has only been found in the gamma-conotoxin family. The molecular mass of the native peptide was determined by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, which confirmed the chemical analyses and suggested a free C-terminus. The purified peptide elicited toxic effects in the freshwater snail Pomacea paludosa after intramuscular injection, but it had no effect when injected intracerebrally into mice. The structural similarity of peptide as7a to other gamma-conotoxins suggests that modulation of pacemaker channels could be responsible for its biological activity.

Putative gamma-conotoxins in vermivorous cone snails: the case of Conus delessertii

Peptide de7a was purified from the venom of Conus delessertii, a vermivorous cone snail collected in the Yucatan Channel, Mexico. Its amino acid sequence was determined by automatic Edman degradation after reduction and alkylation. The sequence shows six Cys residues arranged in the pattern that defines the O-superfamily of conotoxins, and several post-translationally modified residues. The determination of its molecular mass by means of laser desorption ionization time-of-flight mass spectrometry (average mass, 3170.0 Da) confirmed the chemical data and suggested amidation of the C-terminus. The primary structure (ACKOKNNLCAITgammaMAgammaCCSGFCLIYRCS*; O, hydroxyproline; gamma, gamma-carboxyglutamate; *, amidated C-terminus; calculated average mass, 3169.66 Da) of de7a contains a motif (gammaCCS) that has previously only been found in two other toxins, both from molluscivorous cone snails: TxVIIA from Conus textile and gamma-PnVIIA from Conus pennaceus. These toxins cause depolarization and increased firing of action potentials in molluscan neuronal systems, and toxin gamma-PnVIIA has been shown to act as an agonist of neuronal pacemaker cation currents. The similarities to toxins TxVIIA and gamma-PnVIIA suggest that peptide de7a might also affect voltage-gated nonspecific cation pacemaker channels.

Physico-chemical characterization and synthesis of neuronally active alpha-conotoxins

The high specificity of alpha-conotoxins for different neuronal nicotinic acetylcholine receptors makes them important probes for dissecting receptor subtype selectivity. New sequences continue to expand the diversity and utility of the pool of available alpha-conotoxins. Their identification and characterization depend on a suite of techniques with increasing emphasis on mass spectrometry and microscale chromatography, which have benefited from recent advances in resolution and capability. Rigorous physico-chemical analysis together with synthetic peptide chemistry is a prerequisite for detailed conformational analysis and to provide sufficient quantities of alpha-conotoxins for activity assessment and structure-activity relationship studies.

Fragmentation of a novel marine peptide, plicatamide, involves an unusual gas-phase intramolecular rearrangement

During our characterization of plicatamide 1, a modified octapeptide: Phe-Phe-His-Leu-His-Phe-His-dc deltaDOPA (where dc deltaDOPA = decarboxy-(E)-alpha,beta-dehydro-3,4-dihydroxyphenylalanine) from the blood cells of the ascidian Styela plicata, we noted a series of fragment ions from the [M + H]+ ion which could not be assigned. There was no evidence in the 1H NMR spectrum to support an alternative molecular structure and the series of fragment ions were not present in the tandem mass spectrometry analysis of the [M + Na]+ ion. In addition, there was no evidence that the sample was a mixture of isobaric compounds. We propose that an unusual C-terminal to N-terminal rearrangement is responsible for the series of fragment ions from the [M + H]+ ion. This rearrangement was not observed in peptide analogs of plicatamide which did not contain the dc deltaDOPA at the C-terminus suggesting that this moiety is critical for the rearrangement. The proposed reaction is analogous to that recently reported by Vachet et al. involving a fragment ion formed from leucine enkephalin.