Insights into scorpion venom peptides: alternative processing of β-KTx propeptide from Tityus serrulatus venom results in a new naturally occurring thimet oligopeptidase inhibitor

Inhibitors of neuropeptide peptidases engaged in pain and drug dependence

Owing to a broad spectrum of functions performed by neuropeptides, this class of signaling molecules attracts an increasing interest. One of the key steps in the regulation of biological activity of neuropeptides is proteolytic conversion or degradation by proteinases that change or terminate biological activity of native peptides. These enzymes, in turn, are regulated by inhibitors, which play integral role in controlling many metabolic pathways. Thus, the search for selective inhibitors and detailed knowledge on the mechanisms of binding of these substances to enzymes, could be of importance for designing new pharmacological approaches. The aim of this review is to summarize the current knowledge on the inhibitors of enzymes that convert selected groups of neuropeptides, such as dynorphins, enkephalins, substance P and NPFF fragments. The importance of these substances in pathophysiological processes involved in pain and drug addiction, have been discussed. This article is part of the special issue on Neuropeptides.

Potassium channel blockers from the venom of the Brazilian scorpion Tityus serrulatus ()

Potassium (K(+)) channels are trans-membrane proteins, which play a key role in cellular excitability and signal transduction pathways. Scorpion toxins blocking the ion-conducting pore from the external side have been invaluable probes to elucidate the structural, functional, and physio-pathological characteristics of these ion channels. This review will focus on the interaction between K(+) channels and their peptide blockers isolated from the venom of the scorpion Tityus serrulatus, which is considered as the most dangerous scorpion in Brazil, in particular in Minas-Gerais State, where many casualties are described each year. The primary mechanisms of action of these K(+) blockers will be discussed in correlation with their structure, very often non-canonical compared to those of other well known K(+) channels blockers purified from other scorpion venoms. Also, special attention will be brought to the most recent data obtained by proteomic and transcriptomic analyses on Tityus serrulatus venoms and venom glands.

[des-Arg(1)]-Proctolin: A novel NEP-like enzyme inhibitor identified in Tityus serrulatus venom

The scorpion Tityus serrulatus venom comprises a complex mixture of molecules that paralyzes and kills preys, especially insects. However, venom components also interact with molecules in humans, causing clinic envenomation. This cross-interaction may result from homologous molecular targets in mammalians and insects, such as (NEP)-like enzymes. In face of these similarities, we searched for peptides in Tityus serrulatus venom using human NEP as a screening tool. We found a NEP-inhibiting peptide with the primary sequence YLPT, which is very similar to that of the insect neuropeptide proctolin (RYLPT). Thus, we named the new peptide [des-Arg(1)]-proctolin. Comparative NEP activity assays using natural substrates demonstrated that [des-Arg(1)]-proctolin has high specificity for NEP and better inhibitory activity than proctolin. To test the initial hypothesis that molecular homologies allow Tityus serrulatus venom to act on both mammal and insect targets, we investigated the presence of a NEP-like in cockroaches, the main scorpion prey, that could be likewise inhibited by [des-Arg(1)]-proctolin. Indeed, we detected a possible NEP-like in a homogenate of cockroach heads whose activity was blocked by thiorphan and also by [des-Arg(1)]-proctolin. Western blot analysis using a human NEP monoclonal antibody suggested a NEP-like enzyme in the homogenate of cockroach heads. Our study describes for the first time a proctolin-like peptide, named [des-Arg(1)]-proctolin, isolated from Tityus serrulatus venom. The tetrapeptide inhibits human NEP activity and a NEP-like activity in a cockroach head homogenate, thus it may play a role in human envenomation as well as in the paralysis and death of scorpion preys.

New proline-rich oligopeptides from the venom of African adders: Insights into the hypotensive effect of the venoms

BACKGROUND

The snakes from the Bitis genus are some of the most medically important venomous snakes in sub Saharan Africa, however little is known about the composition and effects of these snake venom peptides. Considering that the victims with Bitis genus snakes have exacerbate hypotension and cardiovascular disorders, we investigated here the presence of angiotensin-converting enzyme modulators on four different species of venoms.

METHODS

The peptide fractions from Bitis gabonica gabonica, Bitis nasicornis, Bitis gabonica rhinoceros and Bitis arietans which showed inhibitory activity on angiotensin-converting enzyme were subjected to mass spectrometry analysis. Eight proline-rich peptides were synthetized and their potencies were evaluated in vitro and in vivo.

RESULTS

The MS analysis resulted in over 150 sequences, out of which 32 are new proline-rich oligopeptides, and eight were selected for syntheses. For some peptides, inhibition assays showed inhibitory potentials of cleavage of angiotensin I ten times greater when compared to bradykinin. In vivo tests showed that all peptides decreased mean arterial pressure, followed by tachycardia in 6 out of 8 of the tests.

CONCLUSION

We describe here some new and already known proline-rich peptides, also known as bradykinin-potentiating peptides. Four synthetic peptides indicated a preferential inhibition of angiotensin-converting enzyme C-domain. In vivo studies show that the proline-rich oligopeptides are hypotensive molecules.

GENERAL SIGNIFICANCE

Although proline-rich oligopeptides are known molecules, we present here 32 new sequences that are inhibitors of the angiotensin-converting enzyme and consistent with the symptoms of the victims of Bitis spp, who display severe hypotension.

Neuropeptide Y family-degrading metallopeptidases in the Tityus serrulatus venom partially blocked by commercial antivenoms

Accidents caused by scorpions represent a relevant public health issue in Brazil, being more recurring than incidents with snakes and spiders. The main species responsible for this situation is the yellow scorpion, Tityus serrulatus, due especially to the great frequency with which accidents occur and the potential of its venom to induce severe clinical manifestations, even death, mainly among children. Although neurotoxins are well characterized, little information is known about other components of scorpion venoms, such as peptidases, and their effect on envenomation. Previous results from our group showed that the metallopeptidases present in this venom are capable of hydrolyzing the neuropeptide dynorphin 1-13 in vitro, releasing Leu-enkephalin, which may interact with ion channels and promote indirect neurotoxicity. Thus, this study aims to get more information about the effect of toxic peptidase activity present in the venom on biologically active peptides, and to evaluate the in vitro neutralizing potential of commercial antivenoms produced by the Butantan Institute. A set of human bioactive peptides were studied as substrates for the peptidases, and the members of the neuropeptide Y family were found to be the most susceptible ones. All new substrate hydrolyses were totally inhibited by ethylenediaminetetracetic and not blocked by phenylmethanesulfonylfluoride, indicating that metallopeptidases were responsible for the peptidase activity. Also, peptidase activities were only partially inhibited by therapeutic Brazilian scorpion antivenom (SAV) and arachnid antivenom (AAV). The dose-response inhibition by both antivenoms indicates that AAV neutralizes better than SAV at the used doses. These characterizations, unpublished until now, can contribute to the improvement of our knowledge about the venom and envenomation processes by T. serrulatus.