The putative bioactive surface of insect-selective scorpion excitatory neurotoxins. (1/601)

Scorpion neurotoxins of the excitatory group show total specificity for insects and serve as invaluable probes for insect sodium channels. However, despite their significance and potential for application in insect-pest control, the structural basis for their bioactivity is still unknown. We isolated, characterized, and expressed an atypically long excitatory toxin, Bj-xtrIT, whose bioactive features resembled those of classical excitatory toxins, despite only 49% sequence identity. With the objective of clarifying the toxic site of this unique pharmacological group, Bj-xtrIT was employed in a genetic approach using point mutagenesis and biological and structural assays of the mutant products. A primary target for modification was the structurally unique C-terminal region. Sequential deletions of C-terminal residues suggested an inevitable significance of Ile73 and Ile74 for toxicity. Based on the bioactive role of the C-terminal region and a comparison of Bj-xtrIT with a Bj-xtrIT-based model of a classical excitatory toxin, AaHIT, a conserved surface comprising the C terminus is suggested to form the site of recognition with the sodium channel receptor.  (+info)

Purification from black widow spider venom of a protein factor causing the depletion of synaptic vesicles at neuromuscular junctions. (2/601)

The aqueous extract of the venom glands of black widow spiders was fractionated on a column of Sephadex G-200 and then on a column of DEAE-Sephadex A-50 pH 8.2. A protein fraction was obtained that caused a great increase in the frequency of occurrence of miniature end plate potentials at the frog neuromuscular junction, and caused swelling of the nerve terminals and depleted them of their vesicles. The fraction consists of a least four protein components that are similar in their molecular weights (about 130,000) and isoelectric points (ranging from pH 5.2 to 5.5) and are immunologically indistinguishable. It contains no sugar residues and has little or no lipolytic or proteolytic activity. The fraction is toxic to mice and is different from the fractions that act on houseflies, the crayfish stretch receptor and the cockroach heart. It seems pure enough to warrant a detailed study of its site and mode of action.  (+info)

Contribution of potassium conductances to a time-dependent transition in electrical properties of a cockroach motoneuron soma. (3/601)

Contribution of potassium conductances to a time-dependent transition in electrical properties of a cockroach motoneuron soma. The cell body of the cockroach (Periplaneta americana) fast coxal depressor motoneuron (Df) displays a time-dependent change in excitability. Immediately after dissection, depolarization evokes plateau potentials, but after several hours all-or-none action potentials are evoked. Because K channel blockers have been shown to produce a similar transition in electrical properties, we have used current-clamp, voltage-clamp and action-potential-clamp recording to elucidate the contribution of different classes of K channel to the transition in electrical activity of the neuron. Apamin had no detectable effect on the neuron, but charybdotoxin (ChTX) caused a rapid transition from plateau potentials to spikes in the somatic response of Df to depolarization. In neurons that already produced spikes when depolarized, ChTX increased spike amplitude but did not increase their duration nor decrease the amplitude of their afterhyperpolarization. 4-Aminopyridine (4-AP) (which selectively blocks transient K currents) did not cause a transition from plateau potentials to spikes but did enhance oscillations superimposed on plateau potentials. When applied to neurons that already generated spikes when depolarized, 4-AP could augment spike amplitude, decrease the latency to the first spike, and prolong the afterhyperpolarization. Evidence suggests that the time-dependent transition in electrical properties of this motoneuron soma may result, at least in part, from a fall in calcium-dependent potassium current (IK,Ca), consequent on a gradual reduction in [Ca2+ ]i. Voltage-clamp experiments demonstrated directly that outward K currents in this neuron do fall with a time course that could be significant in the transition of electrical properties. Voltage-clamp experiments also confirmed the ineffectiveness of apamin and showed that ChTX blocked most of IK,Ca. Application of Cd2+ (0.5 mM), however, caused a small additional suppression in outward current. Calcium-insensitive outward currents could be divided into transient (4-AP-sensitive) and sustained components. The action-potential-clamp technique revealed that the ChTX-sensitive current underwent sufficient activation during the depolarizing phase of plateau potentials to enable it to shunt inward conductances. Although the ChTX-sensitive conductance apparently makes little contribution to spike repolarization, the ChTX-resistant IK,Ca does make a significant contribution to this phase of the action potential. The 4-AP-sensitive current began to develop during the rising phase of both action potentials and plateau potentials but had little effect on the electrical activity of the neuron, probably because of its relatively small amplitude.  (+info)

cDNA cloning of an adult male putative lipocalin specific to tergal gland aphrodisiac secretion in an insect (Leucophaea maderae). (4/601)

Lma-P22 is a cuticular surface protein specific to the tergal gland secretion of Leucophaea maderae adult males which is ingested by females just before copulation. The complete Lma-P22 cDNA sequence was determined by RT-PCR using primers based on Edman degradation fragments. The recombinant protein expressed in Escherichia coli was recognized by an anti-Lma-P22 antibody. Northern blot analysis indicates that the corresponding mRNA is transcribed only in the epidermis of male tergites. Sequence analysis indicated that Lma-P22 deduced protein belongs to the lipocalin family. Lipocalins are extracellular proteins which carry hydrophobic compounds and some of them can bind sexual pheromone in vertebrates. Lma-P22 is the first example of a lipocalin-like protein involved in insect sexual behavior.  (+info)

Clinical experience and results of a Sentinel Health Investigation related to indoor fungal exposure. (5/601)

This is a review of exposure conditions, clinical presentation, and morbidity of children and adults with indoor fungal exposure such as toxic Stachybotrys chartarum. Indoor exposure was characterized using different methods including microscopic, culture, cytotoxicity screening tests, and chemical analyses. Clinical case histories and physical and laboratory findings are presented of children (age < 18 years, n = 22; mean age 9 years; 60% females) and adults (age >18 years, n = 125; mean age 39 years, 67% females) who consulted an environmental health specialty clinic. In the pediatric patients' exposure history, widespread fungal contamination of water-damaged building materials with known toxic or allergic fungi was identified. Primarily disorders of the respiratory system, skin, mucous membranes, and central nervous system were reported. Some enumeration and functional laboratory abnormalities, mainly of the lymphatic blood cells, were observed, although no statistically significant differences were found. IgE or IgG fungi-specific antibodies, used as exposure markers, were positive in less than 25% of all tested cases. In an evaluation of a symptomatic girl 11 years of age (sentinel case investigation) living in an apartment with verified toxigenic fungi (i.e., S. chartarum), several health indicators showed improvement after exposure cessation.  (+info)

A K+ channel-blocking peptide from venom of Chinese scorpion Buthus martensii Karsch. (6/601)

AIM: To purify and characterize a potassium channel blocker (BmP-3) from the venom of Chinese scorpion Buthus martensii Karsch. METHODS: 1. Purification was carried out by gel-filtration, cation-exchange, and reversed-phase chromatographies. N-terminal was directly sequenced by double-coupling manual method. Molecular weight was determined on an electrospray ionization mass spectrometer. Amino acid composition was analyzed after acidic hydrolysis for 20 h in HCl 6 mol.L-1 at 110 degrees C. 2. Toxicity tests were conducted in mice and cockroaches. 3. The inhibitory effects of BmP-3 on K+ channels were tested in acutely dissociated rat hippocampal pyramidal neurons using whole-cell patch-clamp configuration. RESULTS: 1. A pure peptide (BmP-3, 8.1 mg) was obtained, about 0.08% of total proteins of the venom. The N-terminal sequences were VGCEE and the molecular weight was 2938 in ESI-mass spectra. 2. No death occurred at the dosage of 200 micrograms in mice and 8 micrograms in cockroaches. 3. The peptide at 10 mumol.L-1 reduced the peak outward K+ currents by 63% +/- 4% in vitro. CONCLUSION: BmP-3 inhibited K+ channels.  (+info)

Role of allergy in nasal polyps of Thai patients. (7/601)

As distinct from many countries, allergy in Thailand is of the perennial type which may play a role in the formation of nasal polyps. Forty consecutive patients with nasal polyps and 30 normal subjects as control were studied at the Allergy Clinic, Department of Otolaryngology, Pramongkutklao Hospital. A positive clinical history and skin allergy testing are diagnostic criteria for allergy. In the nasal polyps group, these were 28 males and 12 females, aged between 12-65 years, with an average age of 38.5 years. In the control group, there were 18 males and 12 females, aged between 15-53 yeas, with an average age of 34 years. All had received prick skin testing with 6 common aeroallergens. The prick skin test was considered positive when the wheal was > or = 3 mm with surrounding erythema. Twenty-four of 40 patients (60%) with nasal polyps had a positive prick skin test, while 6 in the 30 control cases (20%) had a positive prick skin test. This difference was statistically significant (P = 0.0019), Odd's ratio = 6.0 which means allergic persons were 6 times more prone to have polyps form than normal persons.  (+info)

Post-translational modifications of the insect sulfakinins: sulfation, pyroglutamate-formation and O-methylation of glutamic acid. (8/601)

We identified and chemically characterized the two major forms of sulfakinins from an extract of 800 corpora cardiaca/corpora allata complexes of the American cockroach, Periplaneta americana. Bioactivity during the purification was monitored by measuring heart beat frequency in a preparation in situ. By Edman degradation analysis and MS, these main forms were identified as having the primary structures Pea-SK [EQFDDY(SO(3)H)GHMRFamide] and Lem-SK-2 [pQSDDY(SO(3)H)GHMRFamide]. The sulfation was confirmed by UV, MS and peptide synthesis. In addition, post-translationally modified sulfakinins of both major forms were isolated and identified. Firstly, nonsulfated forms of these peptides are present in considerable amounts in the corpora cardiaca/allata. Secondly, the N-terminally blocked Pea-SK and the nonblocked Lem-SK-2 occur naturally in neurohaemal release sites. Thirdly, modified Pea-SK with O-methylated glutamic acid occurs which is not an artefact of peptide purification. The major forms of the sulfakinins were shown to be highly active on both the heart and hindgut with threshold concentrations of approximately 5 x 10(-10) M (heart) and 2 x 10(-9) M (hindgut).  (+info)