Solution structure of Hyp10Pro variant of conomarphin, a cysteine-free and d-amino-acid containing conopeptide

Significance of D- tryptophan in Contryphan-Ar1131 Conus peptide: Oxidative folding, trypsin binding, and photostabilization activity

Distinct differences have been observed between L-tryptophan and D-tryptophan containing contryphan-Ar1131 in oxidative folding, trypsin binding, and photostabilization activity on avobenzone. [W⁵] contryphan-Ar1131 and [w⁵] contryphan-Ar1131 were chemically synthesized and characterized using RP-HPLC and mass spectrometry. Structural differences due to the change of configuration of tryptophan were evident from the optimized structures of contryphan-Ar1131 using density functional theory (DFT). The comparison of early events of oxidative folding has revealed the role of D-tryptophan in accelerating the formation of a disulfide bond. The optimized structures of the reduced form of peptides revealed the occurrence of aromatic-aromatic and aromatic-proline interactions in [w⁵] contryphan-Ar1131 which may be critical in aiding the oxidative folding reaction. The presence of the Lys6-Pro7 peptide bond indicates that contryphan-Ar1131 is resistant but may bind to trypsin allowing to assign the binding affinity of peptides to the protein surface. Competitive binding studies and molecular docking along with molecular dynamic (MD) simulations have revealed that [w⁵] contryphan-Ar1131 has more affinity for the active site of trypsin. Given tryptophan is a photostabilizer of FDA-approved chemical UV-A filter avobenzone, the report has compared the photostabilization activity of [W⁵]/ [w⁵] contryphan-Ar1131 on avobenzone under natural sunlight. [w⁵] contryphan-Ar1131 has better photostabilization activity than that of [W⁵] contryphan-Ar1131 and also individual D-tryptophan and L-tryptophan amino acids. These biochemical studies have highlighted the significance of D-tryptophan in contryphan-Ar1131 and its photostabilization activity on avobenzone may find applications in cosmetics.

In the picture: disulfide-poor conopeptides, a class of pharmacologically interesting compounds

During evolution, nature has embraced different strategies for species to survive. One strategy, applied by predators as diverse as snakes, scorpions, sea anemones and cone snails, is using venom to immobilize or kill a prey. This venom offers a unique and extensive source of chemical diversity as it is driven by the evolutionary pressure to improve prey capture and/or to protect their species. Cone snail venom is an example of the remarkable diversity in pharmacologically active small peptides that venoms can consist of. These venom peptides, called conopeptides, are classified into two main groups based on the number of cysteine residues, namely disulfide-rich and disulfide-poor conopeptides. Since disulfide-poor conotoxins are minor components of this venom cocktail, the number of identified peptides and the characterization of these peptides is far outclassed by its cysteine-rich equivalents. This review provides an overview of 12 families of disulfide-poor peptides identified to date as well as the state of affairs.

Peptidomics of Acanthoscurria gomesiana spider venom reveals new toxins with potential antimicrobial activity

Acanthoscurria gomesiana is a Brazilian spider from the Theraphosidae family inhabiting regions of Southeastern Brazil. Potent antimicrobial peptides as gomesin and acanthoscurrin have been discovered from the spider hemolymph in previous works. Spider venoms are also recognized as sources of biologically active peptides, however the venom peptidome of A. gomesiana remained unexplored to date. In this work, a MS-based workflow was applied to the investigation of the spider venom peptidome. Data-independent and data-dependent LC-MS/MS acquisitions of intact peptides and of peptides submitted to multiple enzyme digestions, followed by automated chromatographic alignment, de novo analysis, database and homology searches with manual validations showed that the venom is composed by <165 features, with masses ranging from 0.4-15.8kDa. From digestions, 135 peptides were identified from 17 proteins, including three new mature peptides: U1-TRTX-Agm1a, U1-TRTX-Agm2a and U1-TRTX-Agm3a, containing 3, 4 and 3 disulfide bonds, respectively. The toxins U1-TRTX-Agm1a differed by only one amino acid from U1-TRTX-Ap1a from A. paulensis and U1-TRTX-Agm2a was derived from the genicutoxin-D1 precursor from A. geniculata. These toxins have potential applications as antimicrobial agents, as the peptide fraction of A. gomesiana showed activity against Escherichia coli, Enterobacter cloacae and Candida albicans strains. MS data are available via ProteomeXchange Consortium with identifier PXD003884.

BIOLOGICAL SIGNIFICANCE

Biological fluids of the Acanthoscurria gomesiana spider are sources of active molecules, as is the case of antimicrobial peptides and acylpolyamines found in the hemolymphs. The venom is also a potential source of toxins with pharmacological and biotechnological applications. However, to our knowledge no A. gomesiana venom toxin structure has been determined to date. Using a combination of high resolution mass spectrometry, transcriptomics and bioinformatics, we employed a workflow to fully sequence, determine the number of disulfide bonds of mature peptides and we found new potential antimicrobial peptides. This workflow is suitable for complete peptide toxin sequencing when handling limited amount of venom samples and can accelerate the discovery of peptides with potential biotechnological applications.

Structural and Functional Characterization of a Novel α-Conotoxin Mr1.7 from Conus marmoreus Targeting Neuronal nAChR α3β2, α9α10 and α6/α3β2β3 Subtypes

In the present study, we synthesized and, structurally and functionally characterized a novel α4/7-conotoxin Mr1.7 (PECCTHPACHVSHPELC-NH2), which was previously identified by cDNA libraries from Conus marmoreus in our lab. The NMR solution structure showed that Mr1.7 contained a 310-helix from residues Pro7 to His10 and a type I β-turn from residues Pro14 to Cys17. Electrophysiological results showed that Mr1.7 selectively inhibited the α3β2, α9α10 and α6/α3β2β3 neuronal nicotinic acetylcholine receptors (nAChRs) with an IC50 of 53.1 nM, 185.7 nM and 284.2 nM, respectively, but showed no inhibitory activity on other nAChR subtypes. Further structure-activity studies of Mr1.7 demonstrated that the PE residues at the N-terminal sequence of Mr1.7 were important for modulating its selectivity, and the replacement of Glu2 by Ala resulted in a significant increase in potency and selectivity to the α3β2 nAChR. Furthermore, the substitution of Ser12 with Asn in the loop2 significantly increased the binding of Mr1.7 to α3β2, α3β4, α2β4 and α7 nAChR subtypes. Taken together, this work expanded our knowledge of selectivity and provided a new way to improve the potency and selectivity of inhibitors for nAChR subtypes.

Nutritional and medicinal aspects of D-amino acids

This paper reviews and interprets a method for determining the nutritional value of D-amino acids, D-peptides, and amino acid derivatives using a growth assay in mice fed a synthetic all-amino acid diet. A large number of experiments were carried out in which a molar equivalent of the test compound replaced a nutritionally essential amino acid such as L-lysine (L-Lys), L-methionine (L-Met), L-phenylalanine (L-Phe), and L-tryptophan (L-Trp) as well as the semi-essential amino acids L-cysteine (L-Cys) and L-tyrosine (L-Tyr). The results show wide-ranging variations in the biological utilization of test substances. The method is generally applicable to the determination of the biological utilization and safety of any amino acid derivative as a potential nutritional source of the corresponding L-amino acid. Because the organism is forced to use the D-amino acid or amino acid derivative as the sole source of the essential or semi-essential amino acid being replaced, and because a free amino acid diet allows better control of composition, the use of all-amino-acid diets for such determinations may be preferable to protein-based diets. Also covered are brief summaries of the widely scattered literature on dietary and pharmacological aspects of 27 individual D-amino acids, D-peptides, and isomeric amino acid derivatives and suggested research needs in each of these areas. The described results provide a valuable record and resource for further progress on the multifaceted aspects of D-amino acids in food and biological samples.

Stereochemistry of 4-hydroxyproline affects the conformation of conopeptides

The cis/trans isomerization of 4-hydroxyproline is shown to remarkably affect the conformation of conopeptides with or without disulfide bonds.

D-Maurocalcine, a pharmacologically inert efficient cell-penetrating peptide analogue

Maurocalcine has been the first demonstrated animal toxin acting as a cell-penetrating peptide. Although it possesses competitive advantages, its use as a cell-penetrating peptide (CPP) requires that analogues be developed that lack its characteristic pharmacological activity on ryanodine-sensitive calcium channels without affecting its cell-penetrating and vector efficiencies. Here, we present the synthesis, three-dimensional (1)H NMR structure, and activity of D-maurocalcine. We demonstrate that it possesses all of the desired features for an excellent CPP: preserved structure, lack of pharmacological action, conserved vector properties, and absence of cell toxicity. This is the first report of a folded/oxidized animal toxin in its D-diastereomer conformation for use as a CPP. The protease resistance of this new peptide analogue, combined with its efficient cell penetration at concentrations devoid of cell toxicity, suggests that D-maurocalcine should be an excellent vector for in vivo applications.

Novel conopeptides in a form of disulfide-crosslinked dimer

In our present work, seven conotoxins and conopeptides were cloned from four cone snail species based on the M-superfamily signal peptides. Among them, two conopeptides, Vt3.1 and Vt3.2, showed unusual sequence characteristics. Both of them contained two cysteines that are separated by just one non-cysteine residue. In vitro, the chemically synthesized Vt3.1 formed dimers with different intermolecular disulfide linkages. Only the dimer with crossed disulfides showed bioactivity when injected into the intraventricular region of mice brains. Therefore, Vt3.1 and Vt3.2 represent a new group of conopeptides that form disulfide-crosslinked dimers in vitro and probably in vivo.

Prolyl 4-hydroxylase

Posttranslational modifications can cause profound changes in protein function. Typically, these modifications are reversible, and thus provide a biochemical on-off switch. In contrast, proline residues are the substrates for an irreversible reaction that is the most common posttranslational modification in humans. This reaction, which is catalyzed by prolyl 4-hydroxylase (P4H), yields (2S,4R)-4-hydroxyproline (Hyp). The protein substrates for P4Hs are diverse. Likewise, the biological consequences of prolyl hydroxylation vary widely, and include altering protein conformation and protein-protein interactions, and enabling further modification. The best known role for Hyp is in stabilizing the collagen triple helix. Hyp is also found in proteins with collagen-like domains, as well as elastin, conotoxins, and argonaute 2. A prolyl hydroxylase domain protein acts on the hypoxia inducible factor alpha, which plays a key role in sensing molecular oxygen, and could act on inhibitory kappaB kinase and RNA polymerase II. P4Hs are not unique to animals, being found in plants and microbes as well. Here, we review the enzymic catalysts of prolyl hydroxylation, along with the chemical and biochemical consequences of this subtle but abundant posttranslational modification.