28-year-old woman • weakness • anxiety • altered mental status • Dx?

► Weakness ► Anxiety ► Altered mental status.

Stevens-Johnson syndrome/toxic epidermal necrolysis: treatment with low-dose corticosteroids, vitamin C and thiamine.

We present the case of a 33-year-old woman with no significant past medical history who was admitted to an outside hospital for the abrupt onset of fevers, malaise and a diffuse mucocutaneous rash. Her constellation of symptoms and presentation were most consistent with a diagnosis of Stevens-Johnson syndrome/toxic epidermal necrolysis overlap syndrome secondary to ibuprofen exposure. Her rash continued to worsen and she was transferred to our medical intensive care unit (ICU), where broad-spectrum antibiotics were discontinued and she was treated with supportive care as well as 'low-dose' intravenous hydrocortisone, ascorbic acid (vitamin C) and thiamine (HAT therapy). After starting this therapy, the patient demonstrated a dramatic response with rapid improvement of her cutaneous and mucosal lesions. She was tolerating a diet provided by the hospital on day 4 and was discharged from the ICU a few days later.

Mild cough · wheezing · loud heart sounds · Dx?

A 25-year-old man, who was an active duty US Navy sailor, went to his ship's medical department complaining of a mild cough that he'd had for 2 days. He denied having any fevers, chills, night sweats, angina, or dyspnea. He said he hadn't experienced any exertional fatigue or difficulty completing the rigorous physical tasks of his occupation as an engineman on the ship. The patient had no medical or surgical history of significance, and he wasn't taking any medications or supplements. On exam, he was not in acute distress and his vital signs were within normal limits. Auscultation revealed mild wheezing throughout the upper lung fields and loud heart sounds throughout his chest that were audible even with gentle contact of the stethoscope diaphragm. He had no discernible murmurs, rubs, or gallops. In light of the unusually loud heart sounds heard on exam, we performed an electrocardiogram. The EKG revealed a normal sinus rhythm, slight right axis deviation indicated by tall R-waves in V1 (also suggestive of right ventricular hypertrophy), an incomplete right bundle branch block, and a crochetage sign (a notch in the R-waves of the inferior leads). A chest x-ray revealed a normal-sized heart and dilated pulmonary vasculature suggestive of pulmonary hypertension.

Location of inhibitors bound to group IVA phospholipase A2 determined by molecular dynamics and deuterium exchange mass spectrometry.

An analysis of group IVA (GIVA) phospholipase A(2) (PLA(2)) inhibitor binding was conducted using a combination of deuterium exchange mass spectrometry (DXMS) and molecular dynamics (MD). Models of the GIVA PLA(2) inhibitors pyrrophenone and the 2-oxoamide AX007 docked into the protein were designed on the basis of deuterium exchange results, and extensive molecular dynamics simulations were run to determine protein-inhibitor contacts. The models show that both inhibitors interact with key residues that also exhibit changes in deuterium exchange upon inhibitor binding. Pyrrophenone is bound to the protein through numerous hydrophobic residues located distal from the active site, while the oxoamide is bound mainly through contacts near the active site. We also show differences in protein dynamics around the active site between the two inhibitor-bound complexes. This combination of computational and experimental methods is useful in defining more accurate inhibitor binding sites and can be used in the generation of better inhibitors against GIVA PLA(2).

A virtual screening study of the acetylcholine binding protein using a relaxed-complex approach.

The nicotinic acetylcholine receptor (nAChR) is a member of the ligand-gated ion channel family and is implicated in many neurological events. Yet, the receptor is difficult to target without high-resolution structures. In contrast, the structure of the acetylcholine binding protein (AChBP) has been solved to high resolution, and it serves as a surrogate structure of the extra-cellular domain in nAChR. Here we conduct a virtual screening study of the AChBP using the relaxed-complex method, which involves a combination of molecular dynamics simulations (to achieve receptor structures) and ligand docking. The library screened through comes from the National Cancer Institute, and its ligands show great potential for binding AChBP in various manners. These ligands mimic the known binders of AChBP; a significant subset docks well against all species of the protein and some distinguish between the various structures. These novel ligands could serve as potential pharmaceuticals in the AChBP/nAChR systems.

Thermodynamics of peptide insertion and aggregation in a lipid bilayer.

A variety of biomolecules mediate physiological processes by inserting and reorganizing in cell membranes, and the thermodynamic forces responsible for their partitioning are of great interest. Recent experiments provided valuable data on the free energy changes associated with the transfer of individual amino acids from water to membrane. However, a complete picture of the pathways and the associated changes in energy of peptide insertion into a membrane remains elusive. To this end, computational techniques supplement the experimental data with atomic-level details and shed light on the energetics of insertion. Here, we employed the technique of umbrella sampling in a total 850 ns of all-atom molecular dynamics simulations to study the free energy profile and the pathway of insertion of a model hexapeptide consisting of a tryptophan and five leucines (WL5). The computed free energy profile of the peptide as it travels from bulk solvent through the membrane core exhibits two minima: a local minimum at the water-membrane interface or the headgroup region and a global minimum at the hydrophobic-hydrophilic interface close to the lipid glycerol region. A rather small barrier of roughly 1 kcal mol (-1) exists at the membrane core, which is explained by the enhanced flexibility of the peptide when deeply inserted. Combining our results with those in the literature, we present a thermodynamic model for peptide insertion and aggregation which involves peptide aggregation upon contact with the membrane at the solvent-lipid headgroup interface.

H-ras protein in a bilayer: interaction and structure perturbation.

Ras GTPases become functionally active when anchored to membranes by inserting their lipid modified side chains. Their role in cell division, development, and cancer has made them targets of extensive research efforts, yet the mechanism of membrane insertion and the structure of the resulting complex remain elusive. Recently, the structure of the full-length H-ras protein in a DMPC bilayer has been computationally characterized. Here, the atomic interactions between the H-ras membrane anchor and the DMPC bilayer are investigated in detail. We find that the palmitoylated cysteines and Met182 have dual contributions to membrane affinity: hydrogen bonding by their amides and van der Waals interaction by their hydrophobic side chains. The polar side chains help maintain the orientation of the anchor. Although the overall structure of the bilayer is similar to that of a pure DMPC, there are localized perturbations. These perturbations depend on the insertion depth and backbone localization of the anchor, which in turn is modulated by the catalytic domain and the linker. The pattern of anchor amide-DMPC phosphate/carbonyl hydrogen bonds and the flexibility of Palm184 are important in discriminating between different modes of ras-DMPC interactions. The results provide structural arguments in support of the proposed participation of ras in the organization of membrane nanoclusters.

Peptide insertion, positioning, and stabilization in a membrane: insight from an all-atom molecular dynamics simulation.

Peptide insertion, positioning, and stabilization in a model membrane are probed via an all-atom molecular dynamics (MD) simulation. One peptide (WL5) is simulated in each leaflet of a solvated dimyristoylglycero-3-phosphate (DMPC) membrane. Within the first 5 ns, the peptides spontaneously insert into the membrane and then stabilize during the remaining 70 ns of simulation time. In both leaflets, the peptides localize to the membrane interface, and this localization is attributed to the formation of peptide-lipid hydrogen bonds. We show that the single tryptophan residue in each peptide contributes significantly to these hydrogen bonds; specifically, the nitrogen heteroatom of the indole ring plays a critical role. The tilt angles of the indole rings relative to the membrane normal in the upper and lower leaflets are approximately 26 degrees and 54 degrees , respectively. The tilt angles of the entire peptide chain are 62 degrees and 74 degrees . The membrane induces conformations of the peptide that are characteristic of beta-sheets, and the peptide enhances the lipid ordering in the membrane. Finally, the diffusion rate of the peptides in the membrane plane is calculated (based on experimental peptide concentrations) to be approximately 6 A(2)/ns, thus suggesting a 500 ns time scale for intermolecular interactions.