Steroid-based facial amphiphiles for stabilization and crystallization of membrane proteins

Amphiphile selection is a critical step for structural studies of membrane proteins (MPs). We have developed a family of steroid-based facial amphiphiles (FAs) that are structurally distinct from conventional detergents and previously developed FAs. The unique FAs stabilize MPs and form relatively small protein–detergent complexes (PDCs), a property considered favorable for MP crystallization. We attempted to crystallize several MPs belonging to different protein families, including the human gap junction channel protein connexin 26, the ATP binding cassette transporter MsbA, the seven-transmembrane G protein-coupled receptor-like bacteriorhodopsin, and cytochrome P450s (peripheral MPs). Using FAs alone or mixed with other detergents or lipids, we obtained 3D crystals of the above proteins suitable for X-ray crystallographic analysis. The fact that FAs enhance MP crystallizability compared with traditional detergents can be attributed to several properties, including increased protein stability, formation of small PDCs, decreased PDC surface flexibility, and potential to mediate crystal lattice contacts.Membrane proteins (MPs) perform essential roles in cellular physiology, account for about one-third of encoded proteins in genomes, and comprise more than one-half of human drug targets. High-resolution molecular structures provide insight into the underlying molecular mechanisms of MPs and a context for organizing the results of functional studies, and they facilitate structure-based drug design. Because of their hydrophobic domains, MPs require the use of detergents and/or lipids for solubilization from membranes. Detergents commonly used to solubilize and stabilize MPs contain long alkyl chains [e.g., dodecyl-β-D-maltoside (DDM)] and typically form large protein–detergent complexes (PDCs) comprised of tens to hundreds of detergent molecules. MP crystals grown from large PDCs typically diffract less well than crystals grown from smaller PDCs (1) and/or suffer lattice defects (i.e., anisotropy and twinning), likely because of poor packing in the lattice and high solvent content (2, 3). In addition, detergent molecules in PDCs are largely disordered and usually do not contribute to rigid crystal contacts. The reduced polar surface area in MPs compared with soluble proteins also impedes crystallization.In recent years, there has been a substantial increase in the success of crystallization of MPs using novel amphiphiles, such as cubic phase-forming lipids or bilayered micelles (bicelles) (4), and fusions with soluble proteins to facilitate crystal contacts (5, 6). Nevertheless, the success rate for growing well-diffracting 3D crystals has been much lower for MPs than soluble proteins, and MPs account for less than 2% of all current entries in the Protein Data Bank (PDB). Consequently, there continues to be a need for identification of amphiphiles that confer stability and crystallizability of MPs. For instance, a variety of novel amphiphiles, including protein-based nanodiscs (7), amphiphilic polymers (8), peptide-based surfactants (9, 10), and maltose-neopentyl glycol (11) or Di-Mal detergents (12), has been widely used for the solubilization and stabilization of MPs for functional or biophysical studies. However, there has been limited success using some of these novel amphiphiles to crystallize MPs (11, 13–15).Another class of widely studied amphiphiles exhibits facial amphiphilicity that is distinct from the end polarity present in conventional head-to-tail detergents. Representative facial amphiphiles (FAs) include bile acids and their derivatives, such as CHAPS and CHAPSO, which have been widely used to solubilize and stabilize integral MPs but have yielded little success in crystallization, despite many years of effort. Here, we present the synthesis and evaluation of newly designed steroid-based FAs, which are structurally different from conventional detergents and previously developed FAs. We show that these unique FAs stabilized MPs from different protein families and yielded diffraction-quality 3D crystals.     

Primary psoas abscess

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Psoas abscess is a painful infection that was once linked to tuberculosis but is now more commonly seen as a complication of intestinal disease. In this article, the authors describe a patient with pain in the leg and buttock in whom herniated disk or lumbosacral strain was initially considered. The patient's persistent fever and the abnormal results of blood cultures led to the diagnosis of primary psoas abscess.     

Streptomycin/Penicillin

Testosterone propionate was administered regularly to patients with microscopically proved carcinoma of the breast. No evidence of permanent control of the disease was obtained. It is emphasized that treatment with hormones of this type should not be substituted for established procedures such as surgical measures or radiation.     

Resorbable plates for the fixation of mandibular fractures: a prospective study.

PURPOSE: The hypothesis for this prospective evaluation is that resorbable plates are equal to the performance of titanium 2-mm plates, regarding healing of the fracture with bone union and restoration of function. To prove this hypothesis, specific end points will be compared with literature norms for titanium 2-mm miniplate rigid fixation. The primary end point variable for this analysis is the union of the fracture and return to normal function. Secondary end point variables included the incidence of complications such as infection, malunion with malocclusion, soft tissue dehiscence, the need for revision surgery, specific technical challenges, operative time, and the learning curve for the surgeon. PATIENTS AND METHODS: This prospective study consisted of a sequential enrollment of 50 fractures that met the inclusion criteria of having a fracture of the mandibular body, symphysis, angle, or ramus, and required an open reduction and internal fixation for stabilization and repair. The resorbable plates and screws used consisted of an amorphous injection molded copolymer of L-lactide/D-lactide/trimethylene carbonate (Inion CPS system, Tampere, Finland). Data were collated and compared with literature norms for titanium plates and also compared with nonrigid fixation data from a prospective study performed on a similar population in the same institution. RESULTS: Clinical and radiographic evaluation indicated union of all fractures at the eighth follow-up visit. Three sites (6%) noted to have clinical signs of infection were treated immediately upon presentation, with fracture union by 8 weeks. There was no need for revision surgery in this series of patients; 12 screw heads fractured during screw placement and were immediately replaced without significant fracture sequelae. CONCLUSION: Based on this limited series of patients, the hypothesis formulated for this study was validated.     

Prevention of thromboembolism in 190 hip arthroplasties: Comparison of LMW heparin andplacebo

Prophylactic efficacy and safety of a low molecular weight (LMW) heparin against postoperative thromboembolic complications were investigated in a double-blind, randomized study. Totally, 210 consecutive patients undergoing total hip replacement were allocated to two groups. Patients in the heparin group received 50 IU anti-Xa per kilo body weight of Logiparin™ once daily, and patients in the placebo group received one daily injection of saline. Additional prophylaxis in all the patients was thigh-length compression stockings beginning on the day of the operation. Deep vein thrombosis was diagnosed by bilateral ascending phlebography between Days 8 and 10 after the operation. Twenty patients were excluded from the evaluation. Thirty of 93 patients in the heparin group compared with 45 of 97 patients in the placebo group suffered a thromboembolic complication during the study (P = 0.02). The postoperative blood loss and total number of blood transfusions in the heparin group were higher than in the placebo group. However, the observed differences were of no clinical importance. Adverse effects, including bleeding complications and wound hematomas, were observed in 13 heparin patients and 7 placebo patients (NS). One patient in each group died.

Thromboprophylaxis with LMW heparin once daily was safe and more effective than the placebo in patients undergoing total hip replacement     

Outcome and risk factors for left ventricular disorders in chronic uraemia

BACKGROUND: Left ventricular disease occurs frequently in dialysis patients.It may be manifest as concentric LV hypertrophy, LV dilatationwith or without LV hypertrophy, or systolic dysfunction. Littleis known concerning the clinical outcome and risk factors forthese disorders. METHODS: A cohort of 432 end-stage renal disease patients who survivedat least 6 months had an echo-cardiogram on initiation of dialysistherapy. Clinical, laboratory and echocardiographic data wasobtained annually during follow-up. RESULTS: On initiation of ESRD therapy 16% of patients had systolic dysfunction,41% concentric LV hypertrophy, 28% LV dilatation, and only 16%had normal echocardiograms. Median time to development of heartfailure was 19 months in patients with systolic dysfunction,38 months in concentric LV hypertrophy and 38 months in LV dilatation.The relative risks of heart failure in the three groups weresignificantly worse than in the normal group, after adjustingfor age, diabetes and ischaemic heart disease. Median survivalwas 38 months in systolic dysfunction, 48 months in concentrichypertrophy, 56 months in LV dilatation, and >66 months inthe normal group. Two hundred and seventy-five patients had a follow-up echocardiogram17 months after starting dialysis therapy together with serialmeasurement of potential risk factors prior to the echocardiogram.On follow-up echocardiogram the degree of concentric LV hypertrophywas independently related to hypertension while on dialysis,older age, and anaemia while on dialysis; the degree of LV dilatationwas related to ischaemic heart disease, anaemia, hypertensionand hypoalbuminemia while on dialysis; the degree of systolicdysfunction was associated with ischaemic heart disease andanaemia during follow-up. CONCLUSIONS: Manifestations of left ventricular disease are frequent andpersistent in chronic uraemia, and are associated with highrisks of heart failure and death. Potentially reversible riskfactors include anaemia, hypertension, hypoalbuminaemia andischaemic heart disease.