Conformational changes of Loxosceles venom sphingomyelinases monitored by circular dichroism

Discovery of broadly-neutralizing antibodies against brown recluse spider and Gadim scorpion sphingomyelinases using consensus toxins as antigens

Broadly-neutralizing monoclonal antibodies are becoming increasingly important tools for treating infectious diseases and animal envenomings. However, designing and developing broadly-neutralizing antibodies can be cumbersome using traditional low-throughput iterative protein engineering methods. Here, we present a new high-throughput approach for the standardized discovery of broadly-neutralizing monoclonal antibodies relying on phage display technology and consensus antigens representing average sequences of related proteins. We showcase the utility of this approach by applying it to toxic sphingomyelinases from the venoms of species from very distant orders of the animal kingdom, the recluse spider and Gadim scorpion. First, we designed a consensus sphingomyelinase and performed three rounds of phage display selection, followed by DELFIA-based screening and ranking, and benchmarked this to a similar campaign involving cross-panning against recombinant versions of the native toxins. Second, we identified two scFvs that not only bind the consensus toxins, but which can also neutralize sphingomyelinase activity of native whole venom in vitro. Finally, we conclude that the phage display campaign involving the use of the consensus toxin was more successful in yielding cross-neutralizing scFvs than the phage display campaign involving cross-panning.

Molecular cloning and functional characterization of recombinant Loxtox from Loxosceles similis venom

Loxoscelism is a recognized public health problem in Brazil, but the venom from Loxosceles similis, which is widespread in Brazil due to its adaptability to the urban environment, remains poorly characterized. Loxtox is a family of phospholipase D enzymes (PLDs), which are the major components of Loxosceles venom and are responsible for the clinical effects of loxoscelism. Loxtox toxins correspond to 15% of L. similis venom gland transcripts, but the Loxtox family of L. similis has yet to be fully described. In this study, we cloned and functionally characterized recLoxtox s1A and recLoxtox s11A. These recombinant toxins exhibited different in vitro activities depending on pH, and recLoxtox s1A had more intense effects on rabbit skin than did recLoxtox s11A in vivo. Both recombinant toxins were used in immunization protocols, and mapping of their epitopes revealed different immunological reactions for the produced immune serums. Additionally, polyclonal antibodies raised against recLoxtox s1A had greater capacity to significantly reduce the in vitro and in vivo effects of L. similis venom. In summary, we obtained and characterized two novel Loxtox isoforms from L. similis venom, which may be valuable biotechnological and immunological tools against loxoscelism.

Inhibitory effects of a sulfated polysaccharide isolated from edible red alga Bangia fusco-purpurea on α-amylase and α-glucosidase

In this study, a sulfated polysaccharide (BFP) was isolated from the edible red alga Bangia fusco-purpurea. Gel-filtration and thin layer chromatographically analyses suggested that BFP was a homogenous polysaccharide. The chemical structural analysis revealed that BFP mainly consisted of galactose together with a small amount of uronic acid, mannose, and glucose. Its molecular mass was estimated to be 133.18 kDa by high-performance liquid chromatography (HPLC) analysis. BFP inhibited α-amylase and α-glucosidase in a concentration-dependent manner. The IC50 values of BFP against α-amylase and α-glucosidase were estimated to be 1.26 ± 0.11 mg/mL and 1.34 ± 0.07 mg/mL, respectively. Kinetic analyses suggested that BFP showed competitive and non-competitive inhibition against α-amylase and α-glucosidase, respectively. Circular dichroism spectral and fluorescence spectral analyses suggested that BFP affects the conformational structures of these enzymes, which may lead to the inhibition of the enzymatic activities.

Abbreviations: Ara: D-arabinose; AnGal: anhydro-L-galactose residues; CD spectroscopy: Circular Dichroism spectroscopy; DNS: dinitrosalicylic acid; FT-IR: fourier transform infrared spectra; Fuc: L-fucose; Gal: D-galactose; Glc: D-glucose; GlcA: D-Glucuronic acid; HPLC: high performance liquid chromatography; Man: D-mannose; pNPG: p-nitrophenyl-α-D-glucoside; TFA: trifluoroacetic acid; TLC: thin-layer chromatography; PMP: 1-phenyl-3-methyl-5-pyrazolone; Xyl: D-xylose

The juxtamembrane linker in neutral sphingomyelinase-2 functions as an intramolecular allosteric switch that activates the enzyme

Neutral sphingomyelinase 2 (nSMase2) produces the bioactive lipid ceramide and has important roles in neurodegeneration, cancer, and exosome formation. Although nSMase2 has low basal activity, it is fully activated by phosphatidylserine (PS). Previous work showed that interdomain interactions within nSMase2 are needed for PS activation. Here, we use multiple approaches, including small angle X-ray scattering, hydrogen-deuterium exchange-MS, circular dichroism and thermal shift assays, and membrane yeast two-hybrid assays, to define the mechanism mediating this interdomain interactions within nSMase2. In contrast to what we previously assumed, we demonstrate that PS binding at the N-terminal and juxtamembrane regions of nSMase2 rather acts as a conformational switch leading to interdomain interactions that are critical to enzyme activation. Our work assigns a unique function for a class of linkers of lipid-activated, membrane-associated proteins. It indicates that the linker actively participates in the activation mechanism via intramolecular interactions, unlike the canonical linkers that typically aid protein dimerization or localization.

Expression and immunological cross-reactivity of LALP3, a novel astacin-like metalloprotease from brown spider (Loxosceles intermedia) venom

Loxosceles spiders' venom comprises a complex mixture of biologically active toxins, mostly consisting of low molecular mass components (2-40 kDa). Amongst, isoforms of astacin-like metalloproteases were identified through transcriptome and proteome analyses. Only LALP1 (Loxosceles Astacin-Like protease 1) has been characterized. Herein, we characterized LALP3 as a novel recombinant astacin-like metalloprotease isoform from Loxosceles intermedia venom. LALP3 cDNA was cloned in pET-SUMO vector, and its soluble heterologous expression was performed using a SUMO tag added to LALP3 to achieve solubility in Escherichia coli SHuffle T7 Express LysY cells, which express the disulfide bond isomerase DsbC. Protein purification was conducted by Ni-NTA Agarose resin and assayed for purity by SDS-PAGE under reducing conditions. Immunoblotting analyses were performed with specific antibodies recognizing LALP1 and whole venom. Western blotting showed linear epitopes from recombinant LALP3 that cross-reacted with LALP1, and dot blotting revealed conformational epitopes with native venom astacins. Mass spectrometry analysis revealed that the recombinant expressed protein is an astacin-like metalloprotease from L. intermedia venom. Furthermore, molecular modeling of LALP3 revealed that this isoform contains the zinc binding and Met-turn motifs, forming the active site, as has been observed in astacins. These data confirmed that LALP3, which was successfully obtained by heterologous expression using a prokaryote system, is a new astacin-like metalloprotease isoform present in L. intermedia venom.

SMase II, a new sphingomyelinase D from Loxosceles laeta venom gland: molecular cloning, expression, function and structural analysis

Sphingomyelinase D (SMase D) present in the venoms of Loxosceles spiders is the principal component responsible for local and systemic effects observed in the loxoscelism. By using "expressed sequencing tag", it was possible to identify, in a L. laeta venom gland library, clones containing inserts coding for proteins with similarity to SMase D. One of these clones was expressed and the recombinant protein compared with the previously characterized SMase I from L. laeta, in terms of their biological, biochemical and structural properties. The new recombinant protein, SMase II, possesses all the biological properties ascribed to the whole venom and SMase I. SMase II shares 40% and 77% sequence similarity with SMase I and Lb3, respectively; the latter, a SMase D isoform from L. boneti, catalytically inactive. Molecular modeling and molecular dynamics simulations were employed to understand the structural basis, especially the presence of an additional disulfide bridge, in an attempt to account for the observed differences in SMases D activity.

The Loxtox protein family in Loxosceles intermedia (Mello-Leitão) venom

We isolated cDNA sequences coding for dermonecrotic/sphingomyelinases factor proteins from the brown spider Loxosceles intermedia, here named Loxtox proteins. The amino acid sequences based on cloned cDNA of several Loxtox proteins revealed at least six distinct groups of proteins expressed in the venom gland. The level of similarity among the toxins varied from 99% to 55%. The finding of several isoforms of Loxtox in the venom of this spider may reflect an evolutionary adaptation for different prey types and reinforces the idea of an efficient mutational mechanism in the venom gland of spiders.

Enzymatic activation of voltage-gated potassium channels

Voltage-gated ion channels in excitable nerve, muscle, and endocrine cells generate electric signals in the form of action potentials. However, they are also present in non-excitable eukaryotic cells and prokaryotes, which raises the question of whether voltage-gated channels might be activated by means other than changing the voltage difference between the solutions separated by the plasma membrane. The search for so-called voltage-gated channel activators is motivated in part by the growing importance of such agents in clinical pharmacology. Here we report the apparent activation of voltage-gated K+ (Kv) channels by a sphingomyelinase.

Kinetic and mechanistic characterization of the Sphingomyelinases D from Loxosceles intermedia spider venom

Envenomation by arachnids of the genus Loxosceles leads to local dermonecrosis and serious systemic toxicity mainly induced by sphingomyelinases D (SMase D). These enzymes catalyze the hydrolysis of sphingomyelin resulting in the formation of ceramide-phosphate and choline as well as the cleavage of lysophosphatidyl choline generating the lipid mediator lysophosphatidic acid. We have, previously, cloned and expressed two functional SMase D isoforms, named P1 and P2, from Loxosceles intermedia venom and comparative protein sequence analysis revealed that they are highly homologous to SMase I from Loxosceles laeta which folds to form an (alpha/beta)8 barrel. In order to further characterize these proteins, pH dependence kinetic experiments and chemical modification of the two active SMases D isoforms were performed. We show here that the amino acids involved in catalysis and in the metal ion binding sites are strictly conserved in the SMase D isoforms from L. intermedia. However, the kinetic studies indicate that SMase P1 hydrolyzes sphingomyelin less efficiently than P2, which can be attributed to a substitution at position 203 (Pro-Leu) and local amino acid substitutions in the hydrophobic channel that could probably play a role in the substrate recognition and binding.