Protein encapsulation in liposomes: efficiency depends on interactions between protein and phospholipid bilayer.

BACKGROUND: We investigated the encapsulation mechanism of enzymes into liposomes. The existing protocols to achieve high encapsulation efficiencies are basically optimized for chemically stable molecules. Enzymes, however, are fragile and encapsulation requires in addition the preservation of their functionality. Using acetylcholinesterase as a model, we found that most protocols lead to a rapid denaturation of the enzyme with loss in the functionality and therefore inappropriate for such an application. The most appropriate method is based on lipid film hydration but had a very low efficiency. RESULTS: To improve it and to propose a standard procedure for enzyme encapsulation, we separate each step and we studied the effect of each parameter on encapsulation: lipid and buffer composition and effect of the different physical treatment as freeze-thaw cycle or liposomes extrusion. We found that by increasing the lipid concentration, increasing the number of freeze-thaw cycles and enhancing the interactions of the enzyme with the liposome lipid surface more than 40% of the initial total activity can be encapsulated. CONCLUSION: We propose here an optimized procedure to encapsulate fragile enzymes into liposomes. Optimal encapsulation is achieved by induction of a specific interaction between the enzyme and the lipid surface

A Review of Transcatheter Ablation for the Treatment of AVNRT in Children

Background: Atrioventricular nodal reentrant tachycardia (AVNRT) is an arrhythmia due to re-entrant rhythm within the region of the atrioventricular (AV) node, which accounts for most supraventricular tachycardia (SVT) cases in children. There are two main pathways involved for the re-entrant rhythm, slow and fast pathways, with different anatomic locations and involvement in the circuit associated with AVNRT. AVNRT is rare in newborns, but an increase of prevalence throughout childhood was previously reported.Study Objective/Purpose: Currently, Radiofrequency (RF) ablation is the primary method for the treatment of AVNRT in pediatrics. However, multiple modalities with varying efficacies can also be utilized. In this study, we attempt to review indications and complications of the gold-standard use of RF compared to newer modalities for the ablation treatment of AVNRT in the pediatric population. Results/Discussion: Currently there are two transcatheter ablations methods widely applied as AVNRT treatment: RF ablation and Cryoablation (Cryo). Indications for these methods vary with blood flow in the target area, duration of procedure, and risk of recurrence of AVNRT. Both methods have success rates \u3e90% in AVNRT children, with a 3% complication rate. AV block is the most common complication of RF ablation cases, while Cryo, being a newer technology, requires further investigation. Factors that complicate ablation in AVNRT include anatomical and electrophysiological variations between individuals. Fluoroscopic visualization and 3D-voltage mapping of pathways can provide markers for catheter ablation in AVNRT cases to expedite ablation success and enhance safety. Other predictors of success include: reduced fluoroscopy time, lower patient weight, the ability to induce junctional rhythm in the patient during the procedure, and the utilization of image-based guidance and ice-mapping during the ablation. Conclusion: Radiofrequency catheter ablation remains the highly successful gold standard for the treatment of AVNRT in children, with low complication rates. Cryoablation and other advanced techniques are emerging as new methods tailored to the accessory pathways and more sophisticated structural variations underlying AVNRT in children

Three-dimensional view of ultrafast dynamics in photoexcited bacteriorhodopsin

Bacteriorhodopsin (bR) is a light-driven proton pump. The primary photochemical event upon light absorption is isomerization of the retinal chromophore. Here we used time-resolved crystallography at an X-ray free-electron laser to follow the structural changes in multiphoton-excited bR from 250 femtoseconds to 10 picoseconds. Quantum chemistry and ultrafast spectroscopy were used to identify a sequential two-photon absorption process, leading to excitation of a tryptophan residue flanking the retinal chromophore, as a first manifestation of multiphoton effects. We resolve distinct stages in the structural dynamics of the all-trans retinal in photoexcited bR to a highly twisted 13-cis conformation. Other active site sub-picosecond rearrangements include correlated vibrational motions of the electronically excited retinal chromophore, the surrounding amino acids and water molecules as well as their hydrogen bonding network. These results show that this extended photo-active network forms an electronically and vibrationally coupled system in bR, and most likely in all retinal proteins

Sampling the conformational energy landscape of a hyperthermophilic protein by engineering key substitutions

Proteins exist as a dynamic ensemble of interconverting substates, which defines their conformational energy landscapes. Recent work has indicated that mutations that shift the balance between conformational substates (CSs) are one of the main mechanisms by which proteins evolve new functions. In the present study, we probe this assertion by examining phenotypic protein adaptation to extreme conditions, using the allosteric tetrameric lactate dehydrogenase (LDH) from the hyperthermophilic bacterium Thermus thermophilus (Tt) as a model enzyme. In the presence of fructose 1, 6 bis-phosphate (FBP), allosteric LDHs catalyze the conversion of pyruvate to lactate with concomitant oxidation of nicotinamide adenine dinucleotide, reduced form (NADH). The catalysis involves a structural transition between a low-affinity inactive 'T-state' and a high-affinity active 'R-state' with bound FBP. During this structural transition, two important residues undergo changes in their side chain conformations. These are R171 and H188, which are involved in substrate and FBP binding, respectively. We designed two mutants of Tt-LDH with one ('1-Mut') and five ('5-Mut') mutations distant from the active site and characterized their catalytic, dynamical, and structural properties. In 1-Mut Tt-LDH, without FBP, the KmPyr is reduced compared with that of the wild type, which is consistent with a complete shifting of the CS equilibrium of H188 to that observed in the R-state. By contrast, the CS populations of R171, kcat and protein stability are little changed. In 5-Mut Tt-LDH, without FBP, KmPyr approaches the values it has with FBP and becomes almost temperature independent, kcat increases substantially, and the CS populations of R171 shift toward those of the R-state. These changes are accompanied by a decrease in protein stability at higher temperature, which is consistent with an increased flexibility at lower temperature. Together, these results show that the thermal properties of an enzyme can be strongly modified by only a few or even a single mutation, which serve to alter the equilibrium and, hence, the relative populations of functionally important native-state CSs, without changing the nature of the CSs themselves. They also provide insights into the types of mutational pathways by which protein adaptation to temperature is achieved.</p

Structure-function-dynamics relationships in the peculiar Planktothrix PCC7805 OCP1: impact of his-tagging and carotenoid type

The orange carotenoid protein (OCP) is a photoactive protein involved in cyanobacterial photoprotection. Here, we report on the functional, spectral and structural characteristics of the peculiar Planktothrix PCC7805 OCP (Plankto-OCP). We show that this OCP variant is characterized by higher photoactivation and recovery rates, and a stronger energy-quenching activity, compared to other OCPs studied thus far. We characterize the effect of the functionalizing carotenoid and of his-tagging on these reactions, and the time scales on which these modifications affect photoactivation. The presence of a His-tag at the C-terminus has a large influence on photoactivation, thermal recovery and PBS-fluorescence quenching, and likewise for the nature of the carotenoid that additionally affects the yield and characteristics of excited states and the ns-s dynamics of photoactivated OCP. By solving the structures of Plankto-OCP in the ECN- and CAN-functionalized states, each in two closely-related crystal forms, we further unveil the molecular breathing motions that animate Plankto-OCP at the monomer and dimer levels. We finally discuss the structural changes that could explain the peculiar properties of Plankto-OCP. - Complete functional characterization of Synechocystis and Planktothrix OCPs - Hitherto unknown structures of ECN- and CAN-functionalized Planktothrix OC

Temperature-dependent macromolecular X-ray crystallography

The dynamical behaviour of crystalline macromolecules and their surrounding solvent as a function of cryo-temperature is reviewed

Head and neck squamous cell carcinoma of unknown primary: Neck dissection and radiotherapy or definitive radiotherapy

Background Management of head and neck carcinoma from unknown primary (HNCUP) remains controversial, with neck dissection and radiotherapy (RT) or definitive RT both commonly used. The purpose of this study was to characterize HNCUP and retrospectively compare outcomes for patients treated with neck dissection + RT versus definitive RT. Methods From 1994 to 2009, 41 patients with HNCUP underwent either neck dissection + RT ( n  = 22) or definitive RT ± concurrent chemotherapy ( n  = 19) at our institution. Treatment outcomes were compared using Kaplan–Meier methods and log‐rank test. Results There were no differences between patients treated with neck dissection + RT and definitive RT in overall survival (OS), progression‐free survival (PFS), locoregional relapse‐free survival (LRFS), freedom from locoregional failure (FFLRG), or freedom from distant failure (FFDF). Among 17 patients who underwent neck dissection + RT for whom human papillomavirus (HPV) status could be determined, HPV(+) patients trended toward improved OS ( p  = .06) and PFS ( p  = .15). Conclusion Neck dissection and postoperative RT resulted in similar outcomes as definitive RT. The prognostic implications of HPV(+) nodes in HNCUP are similar to those in oropharyngeal primary cancers. © 2013 Wiley Periodicals, Inc. Head Neck 36: 1589–1595, 2014Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109313/1/hed23479.pd

Intravesicle Isothermal DNA Replication

<p>Abstract</p> <p>Background</p> <p>Bacterial and viral DNA replication was previously reconstituted <it>in vitro </it>from component parts <abbrgrp><abbr bid="B1">1</abbr><abbr bid="B2">2</abbr><abbr bid="B3">3</abbr><abbr bid="B4">4</abbr></abbrgrp>. Significant advances in building minimal cell-like structures also have been made recently <abbrgrp><abbr bid="B5">5</abbr><abbr bid="B6">6</abbr><abbr bid="B7">7</abbr></abbrgrp>. Combining the two approaches would further attempts to build a minimal cell-like structure capable of undergoing evolution by combining membrane encapsulation and genome replication. Towards this end, we attempted to use purified genomic replication protein components from thermophilic bacterial sources to copy strands of DNA isothermally within lipid vesicles.</p> <p>Findings</p> <p>Bacterial replication components (such as helicases and DNA polymerases) are compatible with methods for the generation of lipid vesicles. Encapsulation inside phospholipid vesicles does not inhibit the activity of bacterial DNA genome replication machinery. Further the described system is efficient at isothermally amplifying short segments of DNA within phospholipid vesicles.</p> <p>Conclusions</p> <p>Herein we show that bacterial isothermal DNA replication machinery is functional inside of phospholipid vesicles, suggesting that replicating cellular mimics can be built from purified bacterial components.</p

ENZO: A Web Tool for Derivation and Evaluation of Kinetic Models of Enzyme Catalyzed Reactions

We describe a web tool ENZO (Enzyme Kinetics), a graphical interface for building kinetic models of enzyme catalyzed reactions. ENZO automatically generates the corresponding differential equations from a stipulated enzyme reaction scheme. These differential equations are processed by a numerical solver and a regression algorithm which fits the coefficients of differential equations to experimentally observed time course curves. ENZO allows rapid evaluation of rival reaction schemes and can be used for routine tests in enzyme kinetics. It is freely available as a web tool, at http://enzo.cmm.ki.si