Functional reconstitution of the nicotinic acetylcholine receptor by CHAPS dialysis depends on the concentrations of salt, lipid, and protein

Schürholz T, Kehne J, Gieselmann A, Neumann E. Functional reconstitution of the nicotinic acetylcholine receptor by CHAPS dialysis depends on the concentrations of salt, lipid, and protein. Biochemistry. 1992;31(21):5067-5077.The detergent CHAPS was found to be the preferable surfactant for the efficient purification and reconstitution of the Torpedo californica nicotinic acetylcholine receptor (AChR). The main result is that the incorporation of the AChR proteins into lipid vesicles by CHAPS dialysis was strongly dependent on the salt and protein concentrations. As monitored by sucrose gradients, by electron microscopy, and by agonist-induced lithium ion flux, the best reconstitution yields were obtained in 0.5 M NaCl at a protein concentration of 0.5 g/L and in 0.84 M NaCl at 0.15 g/L protein. Electron micrographs of receptor molecules, which were incorporated into vesicles, showed single, nonaggregated dimer (M(r) = 580 000) and monomer (M(r) = 290 000) species. CHAPS dialysis at NaCl concentrations < 0.5 M largely reduced the receptor incorporation concomitant with protein aggregation. Electron micrographs of these preparations revealed large protein sheets or ribbons not incorporated into vesicles. The analysis of static and dynamic light scattering demonstrated that the detergent-solubilized AChR molecules aggregate at low lipid contents (less-than-or-equal-to 500 phospholipids/AChR dimer), independent of the salt concentration. AChR proteins eluted from an affinity column with a solution containing 8 mM CHAPS (but no added lipid) still contained 130 +/- 34 tightly bound phospholipids per dimer. The aggregates (about 10 dimers on the average) could be dissociated by readdition of lipid and, interestingly, also by increasing the CHAPS concentration up to 15 mM. This value is much higher than the CMC of CHAPS = 4.0 +/- 0.4 mM, which was determined by surface tension measurements. The data clearly suggest protein-micelle interactions in addition to the association of monomeric detergents with proteins. Furthermore, the concentration of the (free) monomeric CHAPS at the vesicle-micelle transformation in 0.5 M NaCl ([D(W)]c = 3.65 mM) was higher than in 50 mM NaCl ([D(W)]c = 2.8 mM). However, it is suggested that the main effect of high salt concentrations during the reconstitution process is an increase of the fusion (rate) of the ternary protein/lipid/CHAPS complexes with mixed micelles or with vesicular structures, similar to the salt-dependent fusion of vesicles

Pancreatic anastomosis after pancreatoduodenectomy: A position statement by the International Study Group of Pancreatic Surgery (ISGPS)

Background Clinically relevant postoperative pancreatic fistula (grades B and C of the ISGPS definition) remains the most troublesome complication after pancreatoduodenectomy. The approach to management of the pancreatic remnant via some form of pancreatico-enteric anastomosis determines the incidence and severity of clinically relevant postoperative pancreatic fistula. Despite numerous trials comparing diverse pancreatico-enteric anastomosis techniques and other adjunctive strategies (pancreatic duct stenting, somatostatin analogues, etc), currently, there is no clear consensus regarding the ideal method of pancreatico-enteric anastomosis. Methods An international panel of pancreatic surgeons working in well-known, high-volume centers reviewed the best contemporary literature concerning pancreatico-enteric anastomosis and worked to develop a position statement on pancreatic anastomosis after pancreatoduodenectomy. Results There is inherent risk assumed by creating a pancreatico-enteric anastomosis based on factors related to the gland (eg, parenchymal texture, disease pathology). None of the technical variations of pancreaticojejunal or pancreaticogastric anastomosis, such as duct-mucosa, invagination method, and binding technique, have been found to be consistently superior to another. Randomized trials and meta-analyses comparing pancreaticogastrostomy versus pancreaticojejunostomy yield conflicting results and are inherently prone to bias due to marked heterogeneity in the studies. The benefit of stenting the pancreatico-enteric anastomosis to decrease clinically relevant postoperative pancreatic fistula is not supported by high-level evidence. While controversial, somatostatin analogues appear to decrease perioperative complications but not mortality, although consistent data across the more than 20 studies addressing this topic are lacking. The Fistula Risk Score is useful for predicting postoperative pancreatic fistula as well as for comparing outcomes of pancreatico-enteric anastomosis across studies. Conclusion Currently, no specific technique can eliminate development of clinically relevant postoperative pancreatic fistula. While consistent practice of any standardized technique may decrease the rate of clinically relevant postoperative pancreatic fistula, experienced surgeons can have lower postoperative pancreatic fistula rates performing a variety of techniques depending on the clinical situation. There is no clear evidence on the benefit of internal or external stenting after pancreatico-enteric anastomosis. The use of somatostatin analogues may be important in decreasing morbidity after pancreatoduodenectomy, but it remains controversial. Future studies should focus on novel approaches to decrease the rate of clinically relevant postoperative pancreatic fistula with appropriate risk adjustment

Genomic reconstruction of the SARS-CoV-2 epidemic in England

AbstractThe evolution of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus leads to new variants that warrant timely epidemiological characterization. Here we use the dense genomic surveillance data generated by the COVID-19 Genomics UK Consortium to reconstruct the dynamics of 71 different lineages in each of 315 English local authorities between September 2020 and June 2021. This analysis reveals a series of subepidemics that peaked in early autumn 2020, followed by a jump in transmissibility of the B.1.1.7/Alpha lineage. The Alpha variant grew when other lineages declined during the second national lockdown and regionally tiered restrictions between November and December 2020. A third more stringent national lockdown suppressed the Alpha variant and eliminated nearly all other lineages in early 2021. Yet a series of variants (most of which contained the spike E484K mutation) defied these trends and persisted at moderately increasing proportions. However, by accounting for sustained introductions, we found that the transmissibility of these variants is unlikely to have exceeded the transmissibility of the Alpha variant. Finally, B.1.617.2/Delta was repeatedly introduced in England and grew rapidly in early summer 2021, constituting approximately 98% of sampled SARS-CoV-2 genomes on 26 June 2021.</jats:p