Muscarinic toxins from the black mamba Dendroaspis polylepis

Three new toxins acting on muscarinic receptors were isolated from the venom of the black mamba Dendroaspis polylepis. They were called muscarinic toxins alpha, beta, and gamma (MT alpha, MT beta, and MT gamma). All of the toxins have four disulphide bonds and 65 or 66 amino acids. The sequences of MT alpha and MT beta were determined. The muscarinic toxins, of which about 12 have been isolated from venoms of green and black mambas, have 60-98% sequence identity with each other, and are similar to many (about 180) other snake venom components, such as alpha-neurotoxins, cardiotoxins, and fasciculins. In contrast to the alpha-neurotoxins, muscarinic toxins do not bind to nicotinic acetylcholine receptors. The binding constants of MT alpha and MT beta were determined for human muscarinic receptors of subtypes m1-m5 stably expressed in Chinese hamster ovary cells. The toxins are less selective than the earlier discovered muscarinic toxins from the green mamba Dendroaspis angusticeps. MT alpha and the muscarinic toxin MT4 from D. angusticeps differ only in a region of three amino acids (residues 31-33), which are Leu-Asn-His in MT alpha and Ile-Val-Pro in MT4. This difference causes a pronounced shift in subtype selectivity. MT alpha has high affinity to all subtypes, with Ki (inhibition constant) values of 23 nM (m1; pKi = 7.64 +/- 0.10), 44 nM (m2; pKi = 7.36 +/- 0.06), 3 nM (m3; pKi = 8.46 +/- 0.14), 5 nM (m4; pKi = 8.32 +/- 0.07), and 8 nM (m5; pKi = 8.09 +/- 0.07). MT4 has high affinity only to m1 (Ki = 62 nM) and m4 (87 nM) receptors, and low (Ki > 1 microM) affinity to m2, m3, and m5. The region at positions 31-33 evidently plays an important role in the toxin-receptor interaction. MT beta has low affinity for m1 and m2 receptors (Ki > 1 microM) and intermediate affinity for m3 (140 nM; pKi = 6.85 +/- 0.03), m4 (120 nM; pKi = 6.90 +/- 0.06), and m5 (350 nM; pKi = 6.46 +/- 0.01). The low affinity of MT beta may reflect a tendency for spontaneous inactivation.

A study of 51 subtypes of peripheral blood immune cells in newly diagnosed young type 1 diabetes patients

Type 1 diabetes (T1D) results from autoimmune destruction of insulin-producing beta cells in pancreatic islets. Various immune cell populations are involved in disease development and natural course. However, to our knowledge, so far there are no comprehensive comparative investigations of all main immune cell populations and their most important subsets at the onset of disease. Therefore, in the current study, we analyzed 51 peripheral blood immune cell populations in 22 young T1D patients and in 25 age-matched controls using a comprehensive polychromatic flow cytometry panel developed for whole blood by the COST Action no. BM0907 ENTIRE (European Network for Translational Immunology Research and Education: From Immunomonitoring to Personalized Immunotherapy) consortium. We found that in T1D patients, frequencies and absolute counts of natural killer (NK) cells, dendritic cells (DC) and T cells, as well as their respective subsets, were significantly altered compared to controls. Further, we observed that changes in several cell populations (e.g. CD14⁺ CD16⁺ non-classical monocytes, plasmablasts) were dependent on the age of the patient. In addition to age-related changes, we also found that alterations in immune cell patterns were associated with parameters such as the presence of ketoacidosis and C-peptide serum levels. Our study provides a foundation for future studies investigating different cell lineages and their role in T1D and illustrates the value of polychromatic flow cytometry for evaluating all main peripheral immune cells and their subsets in whole blood samples.

Purification and sequence determination of a new muscarinic toxin (MT4) from the venom of the green mamba (Dendroaspis angusticeps)

A toxin which partially inhibited [3H]N-methylscopolamine binding to rat brain muscarinic receptors was purified from the venom of green mamba, Dendroaspis angusticeps. The N-terminal sequence (up to 45 amino acids) was determined by automated Edman degradation of the whole molecule. The complete sequence was elucidated after enzymatic cleavage with endoproteinase Arg-C or endoproteinase Lys-C and peptide fragments purification. The identity of the C-terminal amino acid was confirmed by hydrazinolysis. The new toxin (MT4) had eight half-cystines and 66 amino acids. It differed from muscarinic toxin MT1 by a single substitution in position 57 (arginine in MT1, histidine in MT4), proximal to the sixth half-cystine.

Kinetic evidence for different mechanisms of interaction of black mamba toxins MT alpha and MT beta with muscarinic receptors

By studying the influence of two toxins from the black mamba Dendroaspis polylepis on the kinetics of [3H]-N-methylscopolamine binding to muscarinic acetylcholine receptors from rat cerebral cortex, it was revealed that these toxins, MT alpha and MT beta, interact with the receptors via kinetically distinct mechanisms. MT beta bound to receptors in a one-step, readily reversible process with the dissociation constant K(d)=5.3 microM. The binding mechanism of MTalpha was more complex, involving at least two consecutive steps. A fast receptor-toxin complex formation (K(T)=3.8 microM) was followed by a slow process of isomerisation of this complex (k(i)=1.8 x 10(-2) s(-1), half-time 39 s). A similar two-step interaction mechanism has been established for a related toxin, MT2 from the green mamba D. angusticeps (K(T)=1.4 microM, k(i)=8.3 x 10(-4) s(-1), half-time 840 s). The slow isomerisation process delays the effect of MT alpha and MT2, but increases their apparent potency compared to toxins unable to induce the isomerisation process.

Comprehensive flow cytometric reference intervals of leukocyte subsets from six study centers across Europe

A group of European FOCIS Centers of Excellence adapted panels of the Human Immunophenotyping Consortium (HIPC) for whole blood analysis. Using four core panels [T/regulatory T cell/B/natural killer (T/Treg /B/NK) and myeloid cells] the main leukocyte populations were analyzed in a clinical-diagnostic setting in a harmonized manner across different platforms. As a first step, the consortium presents here the absolute and relative frequencies of the leukocyte subpopulations in the peripheral blood of more than 300 healthy volunteers across six different European centers.

Influence of atropine on carbachol dual effect on Ca2+ mobilization in SH-SY5Y neuroblastoma cells

The muscarinic receptor stimulated mobilisation of calcium ions in SH-SY5Y neuroblastoma cells was measured as a function on carbachol and atropine concentrations. The combined application of this pair of muscarinic agonist and antagonist yielded a set of bell-shaped dose-response curves. In the presence of atropine the cell responses were smaller and the up-going phase of these relationships was shifted towards higher agonist concentration, while the down-going phase of these curves was not influenced by the antagonist. These results pointed to a similar mechanism of the receptor inhibition at high carbachol (agonist) concentrations and by atropine (antagonist).