A bacterial source for mollusk pyrone polyketides

In the oceans, secondary metabolites often protect otherwise poorly defended invertebrates, such as shell-less mollusks, from predation. The origins of these metabolites are largely unknown, but many of them are thought to be made by symbiotic bacteria. In contrast, mollusks with thick shells and toxic venoms are thought to lack these secondary metabolites because of reduced defensive needs. Here, we show that heavily defended cone snails also occasionally contain abundant secondary metabolites, γ-pyrones known as nocapyrones, which are synthesized by symbiotic bacteria. The bacteria, Nocardiopsis alba CR167, are related to widespread actinomycetes that we propose to be casual symbionts of invertebrates on land and in the sea. The natural roles of nocapyrones are unknown, but they are active in neurological assays, revealing that mollusks with external shells are an overlooked source of secondary metabolite diversity.

Improved speciation characteristics of PEGylated indocyanine green-labeled Panitumumab: revisiting the solution and spectroscopic properties of a near-infrared emitting anti-HER1 antibody for optical imaging of cancer

A water-soluble amine-reactive PEGylated analogue of near-infrared emitting dye indocyanine green (5) was synthesized and used to label the anti-HER1 antibody panitumumab (Vectibix) at various equivalents. These conjugates were compared with non-PEGylated analogue conjugate products and the solution speciation analyzed with UV-vis spectrophotometry, size exclusion HPLC, and SDS-PAGE. PEGylation of the bioconjugates was successful in preventing aggregation in solution, a phenomenon observed with the non-PEGylated bioconjugates presumably due to the hydrophobicity of indocyanine green. Competitive radioimmunoassay demonstrated that the targeting moiety of the PEGylated bioconjugates was conserved. Fluorescence microscopy also demonstrated membrane binding of the bioconjugate to HER1-expressing A431 cells. Hence, these bioconjugates are suitable candidates for the in vivo optical imaging of HER1-expressing tumors.

Synthesis and bioactivity of nobilamide B

An alternative and facile solution/solid-phase approach is reported for the total synthesis of neuroactive peptide, nobilamide B. Z-Dhb was formed in solution via EDC/CuCl induced elimination. The solid-phase synthesis employed HBTU/Oxyma Pure™ coupling using Barlos resin. Synthetic nobilamide B was also found to be neuroactive in primary cultures of dorsal root ganglion (DRG) neurons.

The Wheel of Fortune: Helical Wheel Alanine Scanning of a Spider Venom Antimicrobial Peptide Reveals Residues Involved in Antimicrobial and Cytotoxic Activity

A preference for several amino acids is observed to occur at particular positions of cationic α-helical antimicrobial peptides (AMPs), which ensures the formation of amphipathic regions once they assume their correct secondary structure in membranes or membrane-mimicking environments and makes them active against pathogens. This study determined the effect of alanine mutations on the secondary structure and bioactivity of lyp1987 (GRLQAFLAKMKEIAAQTL-NH2), a cationic α-helical AMP obtained from the venom of Lycosa poonaensis which exhibits broad range activity against Gram-positive and Gram-negative bacteria with micromolar minimum inhibitory concentrations (MIC). CD spectroscopy revealed no significant difference in the secondary structure, with all alanine-substituted analogs exhibiting predominantly α-helical structure in buffered 2,2,2-trifluoroethanol solution. Alanine substitution at Glu12 and Thr17 increased the activity of lyp1987 against Gram-positive and -negative bacteria, while alanine substitution at Lys9 increased its selectivity against Gram-positive bacteria. Further investigation can be done to determine positions and substitutions that will give less cytotoxic analogs.

Variable peptide processing of a Conus (Asprella) neocostatus α-conotoxin generates bioactive toxiforms that are potent against distinct nicotinic acetylcholine receptor subtypes

Conusvenoms are composed of peptides that are commonly post-translationally modified, increasing their chemical diversity beyond what is encoded in the genome and enhancing their potency and selectivity. This study describes how PTMs alter an α-conotoxin's selectivity for specific nAChR subtypes. Venom from the cone snailConus(Asprella)neocostatuswas fractionated using high-performance liquid chromatography and tested using a behavioral intracranial mouse bioassay and a cholinergic calcium imaging assay using SH-SY5Y neuroblastoma cells. Four peptides were isolated from three HPLC fractions and found to have similar amino acid sequences using tandem mass spectrometry; they all containC-terminal amidation. The four peptides appear to be encoded by a single gene as indicated by transcriptomic analysis. One of these, NcIA, contains no additional PTM. NcIB lacked the two glycine residues found in the N-terminus of NcIA and contained two hydroxylated prolines. Analogs of both peptides containing a ɣ-carboxylated glutamic residue (NcIA[E15γ] and NcIB[E13γ]) were also isolated. Functional assays revealed distinct receptor selectivity: NcIA inhibited nicotine-evoked responses by over 70 %, while NcIA[E15γ] did not. Conversely, NcIB[E13γ] was inhibitory (∼60 %), but NcIB was not. Against choline-evoked responses, NcIA was weakly inhibitory (∼40 %), whereas the other three were nearly fully inhibitory. The IC50values for NcIB and NcIB[E13γ] were 91.0 nM and 64.7 nM, respectively. These findings indicate that PTMs andN-terminal modifications influence peptide potency and receptor specificity, suggesting that cone snails use variable peptide processing not only to generate chemical diversity in their venom but also to fine-tune the pharmacology of its components.

Total Synthesis and Bioactivity Evaluation of Hydrophobic Microcionamide-Inspired Peptides

In this report, we describe the facile synthesis of four microcionamide-inspired peptides where the atypical 2-phenylethylenamine (2-PEA) functional group in the marine natural product, microcionamide A, was replaced with a similarly-aromatic but more easily incorporated tryptophan (Trp) residue. Compounds 1-4 were synthesized using a standard Fmoc-based solid-phase synthesis strategy followed by iodine-mediated on-resin cyclization for disulfide-bridged compounds 1-3. Compound 1 showed antimicrobial activity against Staphylococcus aureus and Pseudomonas aeruginosa, with minimum inhibitory concentrations (MICs) of 9.1 μM and 15 μM, respectively. The inactivity of alanine analogs 2-4 against these pathogens suggests that the N-terminal Val, the cyclic scaffold, the contiguous Ile residues, and consequently, the hydrophobicity of compound 1 are essential for antibacterial activity. Compound 1 also favorably exhibited minimal cytotoxicity against normal mammalian cell lines. In summary, we have synthesized an analog of microcionamide A where replacement of the 2-PEA moiety with a Trp residue retained the antibacterial activity and with favorably low cytotoxicity.

Neuroactive venom compounds obtained from Phlogiellus bundokalbo as potential leads for neurodegenerative diseases: insights on their acetylcholinesterase and beta-secretase inhibitory activities in vitro

Background

Spider venom is a rich cocktail of neuroactive compounds designed to prey capture and defense against predators that act on neuronal membrane proteins, in particular, acetylcholinesterases (AChE) that regulate synaptic transmission through acetylcholine (ACh) hydrolysis - an excitatory neurotransmitter - and beta-secretases (BACE) that primarily cleave amyloid precursor proteins (APP), which are, in turn, relevant in the structural integrity of neurons. The present study provides preliminary evidence on the therapeutic potential of Phlogiellus bundokalbo venom against neurodegenerative diseases.

Methods

Spider venom was extracted by electrostimulation and fractionated by reverse-phase high-performance liquid chromatography (RP-HPLC) and characterized by matrix-assisted laser desorption ionization-time flight mass spectrometry (MALDI-TOF-MS). Neuroactivity of the whole venom was observed by a neurobehavioral response from Terebrio molitor larvae in vivo and fractions were screened for their inhibitory activities against AChE and BACE in vitro.

Results

The whole venom from P. bundokalbo demonstrated neuroactivity by inducing excitatory movements from T. molitor for 15 min. Sixteen fractions collected produced diverse mass fragments from MALDI-TOF-MS ranging from 900-4500 Da. Eleven of sixteen fractions demonstrated AChE inhibitory activities with 14.34% (± 2.60e-4) to 62.05% (± 6.40e-5) compared with donepezil which has 86.34% (± 3.90e-5) inhibition (p > 0.05), while none of the fractions were observed to exhibit BACE inhibition. Furthermore, three potent fractions against AChE, F1, F3, and F16 displayed competitive and uncompetitive inhibitions compared to donepezil as the positive control.

Conclusion

The venom of P. bundokalbo contains compounds that demonstrate neuroactivity and anti-AChE activities in vitro, which could comprise possible therapeutic leads for the development of cholinergic compounds against neurological diseases.

Norleucine Substitution Enhances Self-Assembly of a Lanthanide-Binding Polypeptide Coiled Coil

A de novo lanthanide-binding coiled-coil polypeptide (MB1-2) was previously reported to self-assemble into a trimeric complex upon addition of Tb3+ with a micromolar range dissociation constant. This study examines the effect of substitution of hydrophobic residues in heptad repeats of MB1-2 on the thermodynamic stability of the resulting Tb-peptide complex. Substitution of isoleucine to norleucine in each heptad repeat was assessed considering the greater accessible surface area of the latter and predicted increased hydrophobic interaction. Job's method of continuous variation using circular dichroism spectroscopy suggests a trimeric structure for the analog complex equivalent to that formed by MB1-2. The dissociation constant and CD spectra suggest that complex formation in the analog is more favorable as a result of ligand preorganization. In addition, thermal denaturation suggests greater stability of the Tb-MB1-2 Nle complex in comparison to the parent Tb-MB1-2. These results indicate improved stability of the complex class can be achieved through heptad repeat amino acid substitutions that increase peptide interchain interaction.

On the inhibition of capsaicin response in dorsal root ganglion neurons by nobilamide B and analogues: a structure–activity relationship study

Nobilamide B, a TRPV1 antagonist, and a series of Ala-substituted analogues were synthesized and their neuroactivity was assessed in a primary culture of dorsal root ganglion (DRG) neurons.

A Gd(III)-labelled self-assembling peptide as a potential pH-responsive MRI contrast agent

A marine-derived peptide labelled with a Gd(III)-chelate was found to self-assemble depending on the solution pH, accompanied by changes in T1-relaxivity (r1) values when in the dispersed or self-assembled form. Such pH-responsive behavior can be advantageous in the development of macromolecular magnetic resonance imaging (MRI) contrast agents which monitor the tissue physiology.