Membrane-protein crystallization in cubo: Temperature-dependent phase behaviour of monoolein-detergent mixtures

The lipidic cubic phase of monoolein has proved to be a matrix well suited to the production of three-dimensional crystals of membrane proteins. It consists of a single continuous bilayer, which is contorted in three-dimensional space and separates two distinct water channels. It has previously been proposed that on the addition of precipitants, membrane proteins embedded in the cubic phase migrate through the matrix to nucleation sites and that this process is dependent upon the stability of the lipidic cubic phase. Here, the effect of detergent type (C-8-C-12 glucosides, C-8-C-12 maltosides and C-7 thioglucoside) and concentration (1-3 x the critical micelle concentration; CMC) on cubic phase stability are reported in the form of the temperature-dependent phase behaviour (268-313 K) in 40% aqueous solution. The results are tabulated to show the best monoolein (MO)-detergent mixtures, mixing temperatures and crystallization temperatures identified. Monoolein-detergent mixtures suited for low-temperature in cubo crystallization of temperature-sensitive proteins are also reported for the first time. These mixtures can be prepared at low temperatures (mixed at less than or equal to 288 K) and remain stable at 277 K for a period of at least one month. They include MO- heptyl thioglucoside (1x and 3x CMC), MO-nonyl glucoside (3 x CMC), MO-octyl maltoside (3 x CMC), MO-nonyl maltoside (1 x CMC) and MO-decyl maltoside (1 x CMC)

Global patient outcomes after elective surgery: prospective cohort study in 27 low-, middle- and high-income countries.

BACKGROUND: As global initiatives increase patient access to surgical treatments, there remains a need to understand the adverse effects of surgery and define appropriate levels of perioperative care. METHODS: We designed a prospective international 7-day cohort study of outcomes following elective adult inpatient surgery in 27 countries. The primary outcome was in-hospital complications. Secondary outcomes were death following a complication (failure to rescue) and death in hospital. Process measures were admission to critical care immediately after surgery or to treat a complication and duration of hospital stay. A single definition of critical care was used for all countries. RESULTS: A total of 474 hospitals in 19 high-, 7 middle- and 1 low-income country were included in the primary analysis. Data included 44 814 patients with a median hospital stay of 4 (range 2-7) days. A total of 7508 patients (16.8%) developed one or more postoperative complication and 207 died (0.5%). The overall mortality among patients who developed complications was 2.8%. Mortality following complications ranged from 2.4% for pulmonary embolism to 43.9% for cardiac arrest. A total of 4360 (9.7%) patients were admitted to a critical care unit as routine immediately after surgery, of whom 2198 (50.4%) developed a complication, with 105 (2.4%) deaths. A total of 1233 patients (16.4%) were admitted to a critical care unit to treat complications, with 119 (9.7%) deaths. Despite lower baseline risk, outcomes were similar in low- and middle-income compared with high-income countries. CONCLUSIONS: Poor patient outcomes are common after inpatient surgery. Global initiatives to increase access to surgical treatments should also address the need for safe perioperative care. STUDY REGISTRATION: ISRCTN5181700

New frontiers in single-cell analysis

For this special issue of J. R. Soc. Interface we present an overview of the driving forces behind technological advances in the field of single-cell analysis. These range from increasing our understanding of cellular heterogeneity through to the study of rare cells, areas of research that cannot be tackled effectively using current high-throughput population-based averaging techniques

Barrier crossing by a flexible long chain molecule - The kink mechanism

The problem and related earlier work All the above problems involve the passage of a long chain molecule, through a region in space, where the free energy per segment is higher, thus effectively presenting a barrier for the motion of the molecule. This is what we refer to as the Kramers proble..

Corrections to Some Models of the Curvature Elastic Energy of Inverse Bicontinuous Cubic Phases

Recently a number of papers have appeared which have attempted to measure the curvature elastic coefficients of lipid monolayers from the structural data of inverse bicontinuous cubic phases [1–3]. It has subsequently become apparent that these efforts have been flawed in at least two ways. Firstly, errors have been made in setting physically inappropriate constraints on the differential geometry of the bicontinuous cubic phases and secondly, it has not been appreciated that in the systems which have been studied, the degree and variance of the mean and Gaussian curvature at the interface are so great that three curvature elastic coefficients are insufficient to correctly describe the bending energetics. In this paper we have re-cast and corrected the curvature elastic description used in references [1–3] and then re-analysed the experimental data with the revised theory. Of course a we have already stated these analyses are inadequate measurements of the curvature elasticity, both in terms of the model used and also because of the relative increase in the energetic contribution from packing frustration and forces acting between bilayers when the lattice parameter is relatively small. However, all is not lost and we show that inverse bicontinuous cubic structures do exist of sufficient size that a simple curvature elastic model may be an adequate description of the mesophase an hence allow one to measure the curvature elastic modulli

Evidence that membrane curvature distorts the tertiary structure of bacteriorhodopsin

The membrane protein bacteriorhodopsin (bR) can be reconstituted into the membrane of the lipid 1-monoolein (MO). This lipid forms a lyotropic liquid crystalline phase whose membrane has hyperbolic interfacial curvature. Using optical absorption spectroscopy and small angle X-ray scattering we have observed retinal unbinding from bR that is correlated with the degree of membrane interfacial curvature. The evidence suggests that bR is susceptible to membrane induced saddle splay for modest perturbations from equilibrium, but for more extreme distortions becomes stiff and resists membrane induced curvature