Botulinum neurotoxins B and E translocate at different rates and exhibit divergent responses to GT1b and low pH.

Botulinum neurotoxins (BoNTs, serotypes A-G) are the most deadly substances known. Here, we investigated how BoNT/E, a serotype that causes human botulism, translocates into the cytosol of neurons. Analogous to BoNT/B, BoNT/E required binding of the coreceptor, GT1b, to undergo significant secondary structural changes and transform into a hydrophobic protein at low pH. These data indicate that both serotypes act as coincidence detectors for both GT1b and low pH, to undergo translocation. However, BoNT/E translocated much more rapidly than BoNT/B. Also, BoNT/E required only GT1b, and not low pH, to oligomerize, whereas BoNT/B required both. In further contrast to the case of BoNT/B, low pH alone altered the secondary structure of BoNT/E to some degree and resulted in its premature inactivation. Hence, comparison of two BoNT serotypes revealed that these agents exhibit both convergent and divergent responses to receptor interactions, and pH, in the translocation pathway.

Effects of donor sperm on perinatal and neonatal outcomes resulting from in vitro fertilization-intracytoplasmic sperm injection and embryo transfer cycles: a retrospective cohort study.

Background: The impact of donor sperm on pregnancy outcomes is controversial. The aim of this study was to investigate whether donor sperm in in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) treatment could reduce the rate of live births or increase the incidence of adverse pregnancy outcomes and birth defects in neonates. Methods: This single-centre, retrospective cohort study included 1,559 patients with infertility who received donor sperm at our hospital from 2015 to 2019. All the patients received fresh embryos and underwent first-cycle transfer. After propensity score matching, 4,677 controls who received their partners' sperm were matched at 1:3. Clinical pregnancy, perinatal, and neonatal outcomes were compared between the donor sperm and partner sperm groups. Results: The embryo development was better in the donor sperm group than in the partner sperm group. The high-quality embryo and available embryo rates were significantly higher in the donor sperm group (P<0.05 for both groups). The rate of high-quality embryos transferred from the donor sperm group was higher than that from the partner sperm group (P<0.05). The clinical pregnancy (62.99% vs. 59.65%; P=0.02) and live birth (54.65% vs. 51.59%; P=0.036) rates were higher in the donor sperm group. After adjusting for confounding factors, no significant difference in live birth rates was observed between the two groups (adjusted P=0.057). The low birthweight (18.21% vs. 21.39%; P=0.023) and small for gestational age (SGA) (7.60% vs. 11.97%; P<0.001) rates were lower in the donor sperm group. To exclude the effect of multiple pregnancies, we evaluated neonatal outcomes of singleton pregnancies. No significant differences were noted in preterm and very preterm birth, SGA, mean birthweight, high birthweight, and low birth weight (LBW) and very low birth weight (VLBW) rates (P>0.05 for both groups). Further, no significant between group differences were observed in the ectopic pregnancy rate, early and late spontaneous abortion rates, gestational age, rate of large for gestational age (LGA), and neonatal defects. Conclusions: Compared with partner sperm, donor sperm did not reduce live birth rate and did not increase neonatal LBW or low birth defects.

Syntaxin requirement for Ca2+-triggered exocytosis in neurons and endocrine cells demonstrated with an engineered neurotoxin.

Botulinum neurotoxins cleave synaptic SNAREs and block exocytosis, demonstrating that these proteins function in neurosecretion. However, the function of the SNARE syntaxin remains less clear because no neurotoxin cleaves it selectively. Starting with a botulinum neurotoxin that cleaves both syntaxin and SNAP-25, we engineered a version that retains activity against syntaxin but spares SNAP-25. These mutants block synaptic release in neurons and norepinephrine release in neuroendocrine cells, thus establishing an essential role for syntaxin in Ca2+-triggered exocytosis. These mutants can generate syntaxin-free cells as a useful experimental system for research and may lead to pharmaceuticals that target syntaxin selectively.

The dramatically increased chaperone activity of small heat-shock protein IbpB is retained for an extended period of time after the stress condition is removed.

sHSP (small heat-shock protein) IbpB (inclusion-body-binding protein B) from Escherichia coli is known as an ATP-independent holding chaperone which prevents the insolubilization of aggregation-prone proteins by forming stable complexes with them. It was found that the chaperone function of IbpB is greatly modulated by the ambient temperature, i.e. when the temperature increases from normal to heat-shock, the chaperone activity of IbpB is dramatically elevated to a level that allows it to effectively bind the aggregation-prone client proteins. Although it is generally believed that the release and refolding of the client protein from the sHSPs depends on the aid of the ATP-dependent chaperones such as Hsp (heat-shock protein) 70 and Hsp100 when the ambient temperature recovers from heat-shock to normal, the behaviour of the sHSPs during this recovery stage has not yet been investigated. In the present study, we examined the behaviour and properties of IbpB upon temperature decrease from heat-shock to normal. We found that IbpB, which becomes functional only under heat-shock conditions, retains the chaperone activity for an extended period of time after the heat-shock stress condition is removed. A detail comparison demonstrates that such preconditioned IbpB is distinguished from the non-preconditioned IbpB by a remarkable conformational transformation, including a significant increase in the flexibility of the N- and C-terminal regions, as well as enhanced dynamic subunit dissociation/reassociation. Intriguingly, the preconditioned IbpB displayed a dramatic decrease in its surface hydrophobicity, suggesting that the exposure of hydrophobic sites might not be the sole determinant for IbpB to exhibit chaperone activity. We propose that the maintenance of the chaperone activity for such 'holdases' as sHSPs would be important for cells to recover from heat-shock stress.

Receptor binding enables botulinum neurotoxin B to sense low pH for translocation channel assembly.

Botulinum neurotoxins (BoNTs, serotypes A-G), elaborated by Clostridium botulinum, can induce lethal paralysis and are classified as Category A bioterrorism agents. However, how BoNTs translocate from endosomes into the cytosol of neurons to gain access to their intracellular targets remains enigmatic. We discovered that binding to the ganglioside GT1b, a toxin coreceptor, enables BoNT/B to sense low pH, undergo a significant change in secondary structure, and transform into a hydrophobic oligomeric membrane protein. Imaging of the toxin on lipid bilayers using atomic force microscopy revealed donut-shaped channel-like structures that resemble other protein translocation assemblies. Toosendanin, a drug with therapeutic effects against botulism, inhibited GT1b-dependent BoNT/B oligomerization and in parallel truncated BoNT/B single-channel conductance, suggesting that oligomerization plays a role in the translocation reaction. Thus, BoNT/B functions as a coincidence detector for receptor and low pH to ensure spatial and temporal accuracy for toxin conversion into a translocation channel.