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Michael E. Adams – One of the best experts on this subject based on the ideXlab platform.
Heterodimeric Structure of the Spider Toxin o-Agatoxin IA Revealed by Precursor Analysis and Mass Spectrometry*, 2008Co-Authors: Ameurfina D. Santos$$y, Michael E. Adams, Julita S. Imperial, Tanuja Chaudharyl, Ronald C. Beavis, Brian T. Chait, John P. Hunspergers, Baldomero M. Oliveras, David R. HillyardAbstract:
We report the first molecular characterization of a In the funnel web spider, Agelenopsis Aperta, a large variety precursor sequence for a small, Ca2+ channel blocking, of small polypeptide toxins are present. Two general classes peptide spider toxin, w-agatoxin IA. By integrating have been identified, the p-agatoxins (Skinner et al., 1989), information generated from a molecular genetic ap- which activate Na2+ channels at the insect neuromuscular proach using agatoxin cDNAs with data provided from junction (Adams et al., 1989), and the w-agatoxins. The w-mass spectrometry of the mature toxin, we were able agatoxins specifically inhibit voltage-sensitive Ca2+ channels to deduce the likely mechanisms by which the toxin (Adams et al., 1990; Scott et al., 1990; Mintz et al., 1991,1992; precursor peptide is processed to its mature heterodi- Venema et al., 1992). Four different classes of w-agatoxins meric form. A particularly interesting feature of the have been described, each with divergent biochemical charprepropeptide is the occurrence of two glutamate-rich acteristics and pharmacological specificity (Olivera et al., sequences interposed between the signal sequences, the major peptide toxin, and the minor toxin peptide. Ex-1991; Adams et al., 1992). The first of these to be charactercisio
Agatoxins: ion channel specific toxins from the American funnel web spider, Agelenopsis Aperta.Toxicon : official journal of the International Society on Toxinology, 2004Co-Authors: Michael E. AdamsAbstract:
Agatoxins from Agelenopsis Aperta venom target three classes of ion channels, including transmitter-activated cation channels, voltage-activated sodium channels, and voltage-activated calcium channels. The α-agatoxins are non-competitive, use-dependent antagonists of glutamate receptor channels, and produce rapid but reversible paralysis in insect prey. Their actions are facilitated by the μ-agatoxins, which shift voltage-dependent activation of neuronal sodium channels to more negative potentials, causing spontaneous transmitter release and repetitive action potentials. The ω-agatoxins target neuronal calcium channels, modifying their properties in distinct ways, either through gating modification (ω-Aga-IVA) or by reduction of unitary current (ω-Aga-IIIA). The α-agatoxins and ω-agatoxins modify both insect and vertebrate ion channels, while the μ-agatoxins are selective for insect channels. Agatoxins have been used as selective pharmacological probes for characterization of ion channels in the brain and heart, and have been evaluated as candidate biopesticides.
The solution structure of ω-Aga-IVB, a P-type calcium channel antagonist from venom of the funnel web spider, Agelenopsis Aperta
Journal of Biomolecular NMR, 1995Co-Authors: Michael D. Reily, Venkataraman Thanabal, Michael E. AdamsAbstract:
The 48 amino acid peptides ω-Aga-IVA and ω-Aga-IVB are the first agents known to specifically block P-type calcium channels in mammalian brain, thus complementing the existing suite of pharmacological tools used for characterizing calcium channels. These peptides provide a new set of probes for studies aimed at elucidating the structural basis underlying the subtype specificity of calcium channel antagonists. We used 288 NMR-derived constraints in a protocol combining distance geometry and molecular dynamics employing the program DGII, followed by energy minimization with Discover to derive the three-dimensional structure of ω-Aga-IVB. The toxin consists of a well-defined core region, comprising seven solvent-shielded residues and a well-defined triple-stranded β-sheet. Four loop regions have average backbone rms deviations between 0.38 and 1.31 Å, two of which are well-defined type-II β-turns. Other structural features include disordered C- and N-termini and several conserved basic amino acids that are clustered on one face of the molecule. The reported structure suggests a possible surface for interaction with the channel. This surface contains amino acids that are identical to those of another known P-type calcium channel antagonist, ω-Aga-IVA, and is rich in basic residues that may have a role in binding to the anionic sites in the extracellular regions of the calcium channel.
Susan E. Riechert – One of the best experts on this subject based on the ideXlab platform.
In the spider nursery: indifference, cooperation or antagonism?Journal of Arachnology, 2017Co-Authors: Susan E. Riechert, Jonathan N. Pruitt, Jennifer M. BoscoAbstract:
Based on studies of adult behavior, the desert spider Agelenopsis Aperta (Gertsch, 1934) is considered exemplary of a species exhibiting an aggressive syndrome. This study offers a first examination of the nature of interactions that juvenile A. Aperta engage in during the period when sibs are clustered on a group web. We test the hypothesis that early instar A. Aperta lack the aggressiveness noted for older instars. Our data set is comprised of observations of five weekly feedings offered to 818 sibling pairs, constituting an average of 4.6 replicate sib pairs from each of 174 families. At each weekly feeding, a worker termite was offered to each sib in the shared container in which they had built web retreats. We observed no cooperative foraging during the course of these feedings. Rather, most families exhibited a mix of independent foraging and non-injurious contests over prey. We present a brief overview of the occurrence and initiation of contests over prey, with particular reference to the weekly feeding in which contests first occur versus the feeding in which a seminal contest takes place (i.e., where sibs earn permanent winner versus loser status).
Molecular evidence for Pleistocene glacial cycles driving diversification of a North American desert spider, Agelenopsis Aperta.Molecular ecology, 2004Co-Authors: Nadia A. Ayoub, Susan E. RiechertAbstract:
The influence of historical climatic vs. geological changes on species diversification patterns was investigated in a widely distributed North American desert spider, Agelenopsis Aperta (Araneae: Agelenidae), with particular reference to Pleistocene glacial cycles and earlier patterns of mountain building. Levels of sequence divergence obtained from the mitochondrial gene, cytochrome oxidase I, dated to the Pleistocene, eliminating Rocky Mountain orogeny as a cause of diversification, as orogeny ended 4 million years ago. The results of phylogenetic and network analyses showed the presence of three geographically defined clades, which were consistent with the presence of at least three glacial refugia: (i) east of the Rocky Mountains; (ii) between the Rocky Mountains and Sierra Nevadas; and (iii) west of the Sierra Nevadas. In addition, populations within the Rocky Mountains exhibited significantly lower genetic diversity than populations east of the Rocky Mountains and the haplotypes found within the Rockies were a subset of eastern haplotypes. These patterns suggest that a post-Pleistocene range expansion occurred out of an eastern glacial refugium into the Rocky Mountains. Examination of phylogeographical studies of other North American desert taxa indicated that mountain building explained diversification patterns more effectively for some taxa but Pleistocene climate change was more important for others, including A. Aperta.
Do female spiders select heavier males for the genes for behavioral aggressiveness they offer their offspringEvolution; international journal of organic evolution, 2003Co-Authors: Susan E. Riechert, Philip M. JohnsAbstract:
We explore the hypothesis that females choose to mate with heavier males for the genes for behavioral aggressiveness they offer their offspring in the desert spider, Agelenopsis Aperta. Behavioral aggressiveness is important to competition for limited resources in the field and is thus correlated with the mass spiders achieve. We established four crosses based on the body mass relationships of parents subjected to selection in their natural environment (female mass/male mass: HI/HI, HI/LO, LO/HI, and LO/LO) and reared the F1 offspring in a noncompetitive laboratory environment. Offspring size and mass at maturity were measured, life history parameters recorded, and behavioral aggressiveness scored in a series of tests. Significant familial effects were detected in all of these measures, but pertinent cross effects were observed only in the assays measuring behavioral aggressiveness. The results were summarized in terms of the fitness costs to HI females of mating with LO males (fewer female offspring of the more aggressive phenotypes) and the benefits to LO females of mating with HI males (fewer fearful offspring of both sexes).
Bruce P Bean – One of the best experts on this subject based on the ideXlab platform.
Block of calcium channels in rat neurons by synthetic ω-Aga-IVANeuropharmacology, 1993Co-Authors: Isabelle M Mintz, Bruce P BeanAbstract:
We investigated block of voltage-dependent Ca channels in freshly dissociated rat central and peripheral neurons by the synthetic peptide ω-Aga-IVA. Synthetic ω-Aga-IVA blocked ∼90% of the high-threshold Ca current in cerebellar Purkinje neurons with an estimated Kd of ∼ 1.5 nM, slightly higher than that determined for block by toxin purified from Agelenopsis Aperta venom. At 200 nM, the synthetic peptide blocked a small fraction of current in dorsal root ganglion neurons but had no effect on identified components of current carried by low-threshold T-type channels or by dihydropyridine-sensitive L-type Ca channels. Up to 800 nM synthetic peptide had no effect on the current in sympathetic neurons, carried mainly by ω-conotoxin GVIA-sensitive N-type channels. In spinal cord neurons, the same fraction of high-threshold current was blocked by synthetic peptide or purified toxin. We conclude that synthetic ω-Aga-IVA has the same high selectivity for blocking P-type Ca channels as does toxin purified from spider venom.
Structure and properties of omega-agatoxin IVB, a new antagonist of P-type calcium channels.Molecular pharmacology, 1993Co-Authors: Michael E. Adams, Isabelle M Mintz, M.d. Reily, V. Thanabal, Bruce P BeanAbstract:
A new peptide antagonist of voltage-activated calcium channels was purified from venom of the funnel web spider, Agelenopsis Aperta. This 48-amino acid peptide, omega-agatoxin (omega-Aga)-IVB, was found to be a potent (Kd, approximately 3 nM) blocker of P-type calcium channels in rat cerebellar Purkinje neurons but had no activity against T-type, L-type, or N-type calcium channels in a variety of neurons. The calcium channel-blocking properties of omega-Aga-IVB were similar to those of another toxin, omega-Aga-IVA, which has 71% amino acid identity with omega-Aga-IVB. The 10-fold greater abundance of omega-Aga-IVB in venom allowed structural studies using NMR spectroscopy. The three-dimensional structure derived from NMR data resulted in a proposed disulfide bond configuration for the peptide. Although omega-Aga-IVB has fewer basic and more acidic residues than does omega-Aga-IVA, the two toxins show conservation of positively charged residues in a mid-peptide region that is predicted to form one face of the omega-Aga-IVB molecule. This region may be crucial for high affinity binding to the P-type calcium channel. In contrast, the amino termini of the two toxins have different charges and seem unlikely to be involved in binding to the channel.
inhibition of n and l type ca2 channels by the spider venom toxin omega aga iiiaProceedings of the National Academy of Sciences of the United States of America, 1991Co-Authors: Isabelle M Mintz, Michael E. Adams, Virginia J. Venema, Bruce P BeanAbstract:
omega-Aga-IIIA, an 8.5-kDa peptide toxin isolated from the venom of Agelenopsis Aperta, was found to be a highly potent inhibitor of Ca channels in cardiac muscle and in peripheral and central neurons of rats and frogs. Cardiac L-type Ca channels were completely (Kd approximately 0.6 nM) blocked by omega-Aga-IIIA. In sensory neurons, the toxin inhibited most high-threshold Ca current but not T-type Ca current. omega-Aga-IIIA blocked with similar potency (Kd approximately 1.5 nM) both omega-conotoxin GVIA-sensitive and dihydropyridine-sensitive current components but left a fraction (approximately 35%) of high-threshold current that was also resistant to omega-conotoxin and dihydropyridines. The toxin blocks N- and L-type channels with equal potency and therefore may identify a high-affinity binding site common to these two Ca channel types.