No abstract

We present a computer simulation study of helix folding in alanine homopeptides (ALA)n of length n = 5, 8, 15, and 21 residues. Based on multi-microsecond molecular dynamics simulations at room temperature, we found helix populations and relaxation times increasing from about 6% and ~2 ns for ALA5 to about 60% and ~500 ns for ALA21, and folding free energies decreasing linearly with the increasing number of residues. The helix folding was analyzed with the Optimal Dimensionality Reduction method, yielding coarse-grained kinetic models that provided a detailed representation of the folding process. The shorter peptides, ALA5 and ALA8, tended to convert directly from coil to helix, while ALA15 and ALA21 traveled through several intermediates. Coarse-grained aggregate states representing the helix, coil, and intermediates were heterogeneous, encompassing multiple peptide conformations. The folding involved multiple pathways and interesting intermediate states were present on the folding paths, with partially formed helices, turns, and compact coils. Statistically, helix initiation was favored at both termini, and the helix was most stable in the central region. Importantly, we found the presence of underlying universal local dynamics in helical peptides with correlated transitions for neighboring hydrogen bonds. Overall, the structural and dynamical parameters extracted from the trajectories are in good agreement with experimental observables, providing microscopic insights into the complex helix folding kinetics.

Background Migration of fish bones into abdominal para-aortic tissue after penetrating the junction of 3rd and 4th part of duodenum is incredibly rare. Case presentation A 68-year-old man was admitted to our hospital with persistent colic in the lower abdomen after eating fish two weeks ago. Abdominal computed tomography (CT) scan showed High density streaks along the anterior and lower edges of the 3rd part of duodenum with peripheral exudation and localized peritonitis. Esophagogastroduodenoscopy didn’t find foreign bodies and perforations in the digestive tract. Laparoscopic surgery and intraoperative endoscopy were made to detect foreign bodies and perforation site was found. After transition to open surgery, the fish bone was found in abdominal para-aortic tissue and removed without complications. Postoperative recovery is smooth, and the patient resumed normal diet and was discharged. Conclusions It is difficult to choose a treatment plan for foreign bodies at the 3rd part of the duodenum, because it is difficult to judge the damage caused by the foreign body to the intestine and the positional relationship with the surrounding important organs. Conservative treatment or surgical treatment both have huge risks. The handling of this situation will extremely test the psychology, physical strength and professional experience of the surgeon.

No abstract

No abstract