Crystal Structure of Reovirus Attachment Protein σ1 in Complex with Sialylated Oligosaccharides

Many viruses attach to target cells by binding to cell-surface glycans. To gain a better understanding of strategies used by viruses to engage carbohydrate receptors, we determined the crystal structures of reovirus attachment protein σ1 in complex with α-2,3-sialyllactose, α-2,6-sialyllactose, and α-2,8-di-siallylactose. All three oligosaccharides terminate in sialic acid, which serves as a receptor for the reovirus serotype studied here. The overall structure of σ1 resembles an elongated, filamentous trimer. It contains a globular head featuring a compact β-barrel, and a fibrous extension formed by seven repeating units of a triple β-spiral that is interrupted near its midpoint by a short α -helical coiled coil. The carbohydrate-binding site is located between β-spiral repeats two and three, distal from the head. In all three complexes, the terminal sialic acid forms almost all of the contacts with σ1 in an identical manner, while the remaining components of the oligosaccharides make little or no contacts. We used this structural information to guide mutagenesis studies to identify residues in σ1 that functionally engage sialic acid by assessing hemagglutination capacity and growth in murine erythroleukemia cells, which require sialic acid binding for productive infection. Our studies using σ1 mutant viruses reveal that residues 198, 202, 203, 204, and 205 are required for functional binding to sialic acid by reovirus. These findings provide insight into mechanisms of reovirus attachment to cell-surface glycans and contribute to an understanding of carbohydrate binding by viruses. They also establish a filamentous, trimeric carbohydrate-binding module that could potentially be used to endow other trimeric proteins with carbohydrate-binding properties

Calculation of the relative metastabilities of proteins in subcellular compartments of Saccharomyces cerevisiae

[abridged] Background: The distribution of chemical species in an open system at metastable equilibrium can be expressed as a function of environmental variables which can include temperature, oxidation-reduction potential and others. Calculations of metastable equilibrium for various model systems were used to characterize chemical transformations among proteins and groups of proteins found in different compartments of yeast cells. Results: With increasing oxygen fugacity, the relative metastability fields of model proteins for major subcellular compartments go as mitochondrion, endoplasmic reticulum, cytoplasm, nucleus. In a metastable equilibrium setting at relatively high oxygen fugacity, proteins making up actin are predominant, but those constituting the microtubule occur with a low chemical activity. A reaction sequence involving the microtubule and spindle pole proteins was predicted by combining the known intercompartmental interactions with a hypothetical program of oxygen fugacity changes in the local environment. In further calculations, the most-abundant proteins within compartments generally occur in relative abundances that only weakly correspond to a metastable equilibrium distribution. However, physiological populations of proteins that form complexes often show an overall positive or negative correlation with the relative abundances of proteins in metastable assemblages. Conclusions: This study explored the outlines of a thermodynamic description of chemical transformations among interacting proteins in yeast cells. The results suggest that these methods can be used to measure the degree of departure of a natural biochemical process or population from a local minimum in Gibbs energy.Comment: 32 pages, 7 figures; supporting information is available at http://www.chnosz.net/yeas

The safety and efficacy of ERCP in the pediatric population with standard scopes: Does size really matter?

Experience with endoscopic retrograde cholangiopancreatography in the pediatric population is limited. The aim of this study was to evaluate the outcomes of ERCP in the pediatric population performed by adult gastroenterologists with standard duodenoscopes. This study is a structured retrospective review of endoscopic reports, computerized and paper medical records, and radiographic images of patients under the age of 18 who underwent ERCP for any indication at a tertiary referral centre. Data regarding demographic characteristics and medical history of patients, indications, technical success rate, final clinical diagnosis, and complications were analyzed. Forty-eight children with a mean age of 13 years (range 2-17) underwent a total of 65 ERCPs. The indications of ERCP were as follows; suspected choledocholithiasis (55 %), post-liver transplantation anastomotic biliary strictures (21 %), post-surgical bile duct injury (10 %), choledochal cyst (2 %), recurrent or chronic pancreatitis (10 %), and trauma (2 %). The cannulation success rate in the overall procedure was 93.8 %. Therapeutic interventions were performed in 70.7 % of patients. Post ERCP pancreatitis was the most common complication occurring in 9.2 % of patients, and no procedure related mortality occurred. When performed by well-trained adult gastroenterologists, the use of endoscopic retrograde cholangiopancreatography with standard duodenoscopes is safe in pediatric population