Solution Structure of BmKK4, the First Member of Subfamily α-KTx 17 of Scorpion Toxins,

Unveiling the Diversity and Modifications of Short Peptides in Buthus martensii Scorpion Venom through Liquid Chromatography-High Resolution Mass Spectrometry

More recently, short peptides in scorpion venom have received much attention because of their potential for drug discovery. Although various biological effects of these short peptides have been found, their studies have been hindered by the lack of structural information especially in modifications. In this study, small peptides from scorpion venom were investigated using high-performance liquid chromatography high-resolution mass spectrometry followed by de novo sequencing. A total of 156 sequences consisting of 2~12 amino acids were temporarily identified from Buthus martensii scorpion venom. The identified peptides exhibited various post-translational modifications including N-terminal and C-terminal modifications, in which the N-benzoyl modification was first found in scorpion venom. Moreover, a short peptide Bz-ARF-NH2 demonstrated both N-terminal and C-terminal modifications simultaneously, which is extremely rare in natural peptides. In conclusion, this study provides a comprehensive insight into the diversity, modifications, and potential bioactivities of short peptides in scorpion venom.

A Combinational Strategy upon RNA Sequencing and Peptidomics Unravels a Set of Novel Toxin Peptides in Scorpion Mesobuthus martensii

Scorpion venom is deemed to contain many toxic peptides as an important source of natural compounds. Out of the two hundred proteins identified in Mesobuthus martensii (M. martensii), only a few peptide toxins have been found so far. Herein, a combinational approach based upon RNA sequencing and Liquid chromatography-mass spectrometry/mass spectrometry (LC MS/MS) was employed to explore the venom peptides in M. martensii. A total of 153 proteins were identified from the scorpion venom, 26 previously known and 127 newly identified. Of the novel toxins, 97 proteins exhibited sequence similarities to known toxins, and 30 were never reported. Combining peptidomic and transcriptomic analyses, the peptide sequence of BmKKx1 was reannotated and four disulfide bridges were confirmed within it. In light of the comparison of conservation and variety of toxin amino acid sequences, highly conserved and variable regions were perceived in 24 toxins that were parts of two sodium channel and two potassium channel toxins families. Taking all of this evidences together, the peptidomic analysis on M. martensii indeed identified numerous novel scorpion peptides, expanded our knowledge towards the venom diversity, and afforded a set of pharmaceutical candidates.

Scorpion toxins prefer salt solutions

There is a wide variety of ion channel types with various types of blockers, making research in this field very complicated. To reduce this complexity, it is essential to study ion channels and their blockers independently. Scorpion toxins, a major class of blockers, are charged short peptides with high affinities for potassium channels. Their high selectivity and inhibitory properties make them an important pharmacological tool for treating autoimmune or nervous system disorders. Scorpion toxins typically have highly charged surfaces and-like other proteins-an intrinsic ability to bind ions (Friedman J Phys Chem B 115(29):9213-9223, 1996; Baldwin Biophys J 71(4):2056-2063, 1996; Vrbka et al. Proc Natl Acad Sci USA 103(42):15440-15444, 2006a; Vrbka et al. J Phys Chem B 110(13):7036-43, 2006b). Thus, their effects on potassium channels are usually investigated in various ionic solutions. In this work, computer simulations of protein structures were performed to analyze the structural properties of the key residues (i.e., those that are presumably involved in contact with the surfaces of the ion channels) of 12 scorpion toxins. The presence of the two most physiologically abundant cations, Na(+) and K(+), was considered. The results indicated that the ion-binding properties of the toxin residues vary. Overall, all of the investigated toxins had more stable structures in ionic solutions than in water. We found that both the number and length of elements in the secondary structure varied depending on the ionic solution used (i.e., in the presence of NaCl or KCl). This study revealed that the ionic solution should be chosen carefully before performing experiments on these toxins. Similarly, the influence of these ions should be taken into consideration in the design of toxin-based pharmaceuticals.

The Hpk2-Rrp2 two-component regulatory system of Treponema denticola: a potential regulator of environmental and adaptive responses

Treponema denticola levels in the gingival crevice become elevated as periodontal disease develops. Oral treponemes may account for as much as 40% of the total bacterial population in the periodontal pocket. The stimuli that trigger enhanced growth of T. denticola, and the mechanisms associated with the transmission of these signals, remain to be defined. We hypothesize that the T. denticola open reading frames tde1970 (histidine kinase) and tde1969 (response regulator) constitute a functional two-component regulatory system that regulates, at least in part, responses to the changing environmental conditions associated with the development of periodontal disease. The results presented demonstrate that tde1970 and tde1969 are conserved, universal among T. denticola isolates and transcribed as part of a seven-gene operon in a growth-phase-dependent manner. tde1970 undergoes autophosphorylation and transfers phosphate to tde1969. Henceforth, the proteins encoded by these open reading frames are designated as Hpk2 and Rrp2 respectively. Hpk2 autophosphorylation kinetics were influenced by environmental conditions and by the presence or absence of a PAS domain. It can be concluded that Hpk2 and Rrp2 constitute a functional two-component system that contributes to environmental sensing.

Membrane-disruptive properties of the bioinsecticide Jaburetox-2Ec: implications to the mechanism of the action of insecticidal peptides derived from ureases

Jaburetox-2Ec, a recombinant peptide derived from an urease isoform (JBURE-II), displays high insecticidal activity against important pests such as Spodoptera frugiperda and Dysdercus peruvianus. Although the molecular mechanism of action of ureases-derived peptides remains unclear, previous ab initio data suggest the presence of structural motifs in Jaburetox-2Ec with characteristics similar to those found in a class of pore-forming peptides. Here, we investigated the molecular aspects of the interaction between Jaburetox-2Ec and large unilamellar vesicles. Jaburetox-2Ec displays membrane-disruptive ability on acidic lipid bilayers and this effect is greatly influenced by peptide aggregation. Corroborating with this finding, molecular modeling studies revealed that Jaburetox-2Ec might adopt a well-defined beta-hairpin conformation similar to those found in antimicrobial peptides with membrane disruption properties. In addition, molecular dynamics simulations suggest that the protein is able to anchor at a polar/non-polar interface. In the light of these findings, for the first time it was possible to point out some evidence that the peptide Jaburetox-2Ec interacting with lipid vesicles promotes membrane permeabilization.

NMR solution structure of BmK-βIT, an excitatory scorpion β-toxin without a ‘hot spot’ at the relevant position

BmK-betaIT (previously named as Bm32-VI in the literature), an excitatory scorpion beta-toxin, is purified from the venom of the Chinese scorpion Buthus martensii Karsch. It features a primary sequence typical of the excitatory anti-insect toxins: two contiguous Cys residues (Cys37-Cys38) and a shifted location of the fourth disulfide bridges (Cys38-Cys64), and demonstrates bioactivity characteristic of the excitatory beta-toxins. However, it is noteworthy that BmK-betaIT is not conserved with a glutamate residue at the preceding position of the third Cys residue, and is the first example having a non-glutamate residue at the relevant position in the excitatory scorpion beta-toxin subfamily. The 3D structure of BmK-betaIT is determined with 2D NMR spectroscopy and molecular modeling. The solution structure of BmK-betaIT is closely similar to those of BmK IT-AP and Bj-xtrIT, only distinct from the latter by lack of an alpha(0)-helix. The surface functional patch comparison with those of BmK IT-AP and Bj-xtrIT reveals their striking similarity in the spatial arrangement. These results infer that the functional surface of beta-toxins is composed of two binding regions and a functional site. The main binding site is consisted of hydrophobic residues surrounding the alpha(1)-helix and its preceding loop, which is common to all beta-type scorpion toxins affecting Na(+) channels. The second binding site, which determines the specificity of the toxin, locates at the C-terminus for excitatory insect beta-toxin, while rests at the beta-sheet and its linking loop for anti-mammal toxins. The functional site involved in the voltage sensor-trapping model, which characterizes the function of all beta-toxins, is the negatively charged residue Glu15.

Solution structure of BmP08, a novel short-chain scorpion toxin from Buthus martensi Karsch

A novel short-chain scorpion toxin BmP08 was purified from the venom of the Chinese scorpion Buthus martensi Karsch by a combination of gel-filtration, ion exchange, and reversed-phase chromatography. The primary sequence of BmP08 was determined using the tandem MS/MS technique and Edman degradation, as well as results of NMR sequential assignments. It is composed of 31 amino acid residues including six cysteine residues and shares less than 25% sequence identity with the known alpha-KTx toxins. BmP08 shows no inhibitory activity on all tested voltage-dependent and Ca(2+)-activated potassium channels. The 3D-structure of BmP08 has been determined by 2D-NMR spectroscopy and molecular modeling techniques. This toxin adopts a common alpha/beta-motif, but shows a distinctive local conformation and features a 3(10)-helix and a shorter beta-sheet. The unique structure is closely related to the distinct primary sequence of the toxin, especially to the novel arrangement of S-S linkages in the molecule, in which two disulfide bridges (C(i)-C(j) and C(i+3)-C(j+3)) link covalently the 3(10)-helix with one strand of the beta-sheet structure. The electrostatic potential surface analysis of the toxin reveals salt bridges and hydrogen bonds between the basic residues and negatively charged residues nearby in BmP08, which may be unfavorable for its binding with the known voltage-dependent and Ca(2+)-activated potassium channels. Thus, finding the target for this toxin should be an interesting task in the future.

BmP09, a “Long Chain” Scorpion Peptide Blocker of BK Channels

A novel "long chain" toxin BmP09 has been purified and characterized from the venom of the Chinese scorpion Buthus martensi Karsch. The toxin BmP09 is composed of 66 amino acid residues, including eight cysteines, with a mass of 7721.0 Da. Compared with the B. martensi Karsch AS-1 as a Na(+) channel blocker (7704.8 Da), the BmP09 has an exclusive difference in sequence by an oxidative modification at the C terminus. The sulfoxide Met-66 at the C terminus brought the peptide a dramatic switch from a Na(+) channel blocker toaK(+) channel blocker. Upon probing the targets of the toxin BmP09 on the isolated mouse adrenal medulla chromaffin cells, where a variety of ion channels coexists, we found that the toxin BmP09 specifically blocked large conductance Ca(2+)- and voltage-dependent K(+) channels (BK) but not Na(+) channels at a range of 100 nm concentration. This was further confirmed by blocking directly the BK channels encoded with mSlo1 alpha-subunits in Xenopus oocytes. The half-maximum concentration EC(50) of BmP09 was 27 nm, and the Hill coefficient was 1.8. In outside-out patches, the 100 nm BmP09 reduced approximately 70% currents of BK channels without affecting the single-channel conductance. In comparison with the "short chain" scorpion peptide toxins such as Charybdotoxin, the toxin BmP09 behaves much better in specificity and reversibility, and thus it will be a more efficient tool for studying BK channels. A three-dimensional simulation between a BmP09 toxin and an mSlo channel shows that the Lys-41 in BmP09 lies at the center of the interface and plugs into the entrance of the channel pore. The stable binding between the toxin BmP09 and the BK channel is favored by aromatic pi -pi interactions around the center.