Cluster phases of membrane proteins

A physical scenario accounting for the existence of size-limited submicrometric domains in cell membranes is proposed. It is based on the numerical investigation of the counterpart, in lipidic membranes where proteins are diffusing, of the recently discovered cluster phases in colloidal suspensions. I demonstrate that the interactions between proteins, namely short-range attraction and longer-range repulsion, make possible the existence of stable small clusters. The consequences are explored in terms of membrane organization and diffusion properties. The connection with lipid rafts is discussed and the apparent protein diffusion coefficient as a function of their concentration is analyzed.Comment: 5 pages - enhanced versio

Thermodynamics of nano-cluster phases: a unifying theory

We propose a unifying, analytical theory accounting for the self-organization of colloidal systems in nano- or micro-cluster phases. We predict the distribution of cluter sizes with respect to interaction parameters and colloid concentration. In particular, we anticipate a proportionality regime where the mean cluster size grows proportionally to the concentration, as observed in several experiments. We emphasize the interest of a predictive theory in soft matter, nano-technologies and biophysics.Comment: 4 pages, 1 figur

The Osteology Lesson of Sebastiaen Egbertszn (1619)

In 1619 the Amsterdam Guild of Surgeons commissioned a recognized Dutch painter to make a group portrait of the governors. This masterpiece is known as The Osteology Lesson of Sebastiaen Egbertszn. Egbertszn, praelector anatomiae (lecturer in anatomy), is depicted while demonstrating the human bones using the skeleton of an English pirate. The subject of this painting reminds us of the doctrine of osteology as part of the former surgical training. The lives and work of the represented governors of the guild and their teacher Sebastiaen Egbertszn, as well as details of the skeleton, are discussed after examination of the literature and original guild documents pertaining to the painting. The Osteology Lesson of Sebastiaen Egbertszn (1619) is a group portrait of the governors of the Amsterdam Guild of Surgeons. It represents one of a series of nine anatomy lessons commissioned in the 17th and 18th centuries. Sebastiaen Egbertszn, who was the praelector anatomiae (lecturer in anatomy) at that time, is depicted demonstrating human bone anatomy using the skeleton of an executed pirate. Egbertszn died during a plague epidemic only 2 years after the painting was delivered and the identity of the artist remains contentious to this day. It is exhibited in the Amsterdam Museum in Amsterdam, The Netherlands

A Realistic Model under which the Genetic Code is Optimal

The genetic code has a high level of error robustness. Using values of hydrophobicity scales as a proxy for amino acid character, and the Mean Square measure as a function quantifying error robustness, a value can be obtained for a genetic code which reflects the error robustness of that code. By comparing this value with a distribution of values belonging to codes generated by random permutations of amino acid assignments, the level of error robustness of a genetic code can be quantified. We present a calculation in which the standard genetic code is shown to be optimal. We obtain this result by (1) using recently updated values of polar requirement as input; (2) fixing seven assignments (Ile, Trp, His, Phe, Tyr, Arg, and Leu) based on aptamer considerations; and (3) using known biosynthetic relations of the 20 amino acids. This last point is reflected in an approach of subdivision (restricting the random reallocation of assignments to amino acid subgroups, the set of 20 being divided in four such subgroups). The three approaches to explain robustness of the code (specific selection for robustness, amino acid-RNA interactions leading to assignments, or a slow growth process of assignment patterns) are reexamined in light of our findings. We offer a comprehensive hypothesis, stressing the importance of biosynthetic relations, with the code evolving from an early stage with just glycine and alanine, via intermediate stages, towards 64 codons carrying todays meaning.Comment: 22 pages, 3 figures, 4 tables Journal of Molecular Evolution, July 201

Staging Laparoscopy for Hilar Cholangiocarcinoma: Is it Still Worthwhile?

This study was designed to evaluate the benefit of staging laparoscopy (SL) in patients with suspected hilar cholangiocarcinoma (HCCA) during the past 10 years. Only 50-60% of patients with HCCA who undergo laparotomy are ultimately amenable to a potentially curative resection. In a previous study, we recommended routine use of SL to prevent unnecessary laparotomies. The accuracy of imaging techniques, however, has significantly improved during the past decade, which is likely to impact the yield and accuracy of SL. From 2000 to 2010, 195 patients with suspected HCCA were analyzed. The yield and accuracy of SL were calculated by dividing total number of avoided laparotomies by the total number of laparoscopies or by all patients with unresectable disease, respectively. Factors associated with better yield and accuracy were assessed. Of 195 patients with HCCA, 175 underwent SL. The yield of SL was 14% and the accuracy was 32%. Operative morbidity of SL was 3%, and operative morbidity of laparotomy for unresectable disease was 33%. No clear factors that influenced the yield of SL were found. Overall yield and accuracy of SL for HCCA in the present series decreased to 14% and 32%, respectively, compared with earlier reports. This finding is likely the result of improved imaging techniques that evolved during the past decade. The place of SL in the workup of patients with HCCA needs to be reconsidered, and one should decide whether the declining additional value of SL still outweighs the drawbacks of S

Hypothermic in situ perfusion of the porcine liver using Celsior or Ringer-lactate solution

BACKGROUND: Hypothermic perfusion (HP) of the liver is applied during total vascular exclusion (TVE) to reduce ischemic injury during liver resection. No studies have been performed comparing different perfusion solutions for HP. The aim of this experimental study was to compare Ringer-lactate solution (RL) with Celsior solution (Cs) for HP in a pig model of 60-min TVE. METHOD: Twenty pigs underwent 60-min TVE of the liver. Groups were TVE without HP (no-HP, n = 9), TVE with HP using RL (n = 6), and TVE with HP using Cs (n = 5). Blood and liver tissue samples were taken before TVE and during 24-h reperfusion. RESULTS: In the no-HP group, plasma aspartate aminotransferase values were significantly increased during reperfusion (p <0.05), while liver tissue pO(2) levels (p <0.01) were decreased when compared to the HP groups. After 24-h reperfusion, bile production and liver tissue glutathione content were significantly higher (p <0.05) in the Cs group (42.0 +/- 1.7 mL/h and 44.9 +/- 2.2 nmol/mg, respectively) as compared to the RL group (31.5 +/- 3.5 mL/h and 19.6 +/- 1.8 nmol/mg, respectively). CONCLUSION: The protective effect of HP during TVE was confirmed in this study. HP with Cs was more effective in reducing ischemic injury as compared to HP with R