A Mechanistic View of the Role of E3 in Sumoylation

Sumoylation, the covalent attachment of SUMO (Small Ubiquitin-Like Modifier) to proteins, differs from other Ubl (Ubiquitin-like) pathways. In sumoylation, E2 ligase Ubc9 can function without E3 enzymes, albeit with lower reaction efficiency. Here, we study the mechanism through which E3 ligase RanBP2 triggers target recognition and catalysis by E2 Ubc9. Two mechanisms were proposed for sumoylation. While in both the first step involves Ubc9 conjugation to SUMO, the subsequent sequence of events differs: in the first E2-SUMO forms a complex with the target and E3, followed by SUMO transfer to the target. In the second, Ubc9-SUMO binds to the target and facilitates SUMO transfer without E3. Using dynamic correlations obtained from explicit solvent molecular dynamic simulations we illustrate the key roles played by allostery in both mechanisms. Pre-existence of conformational states explains the experimental observations that sumoylation can occur without E3, even though at a reduced rate. Furthermore, we propose a mechanism for enhancement of sumoylation by E3. Analysis of the conformational ensembles of the complex of E2 conjugated to SUMO illustrates that the E2 enzyme is already largely pre-organized for target binding and catalysis; E3 binding shifts the equilibrium and enhances these pre-existing populations. We further observe that E3 binding regulates allosterically the key residues in E2, Ubc9 Asp100/Lys101 E2, for the target recognition

Disturbance of Glucose Homeostasis After Pediatric Cardiac Surgery

This study aimed to evaluate the time course of perioperative blood glucose levels of children undergoing cardiac surgery for congenital heart disease in relation to endogenous stress hormones, inflammatory mediators, and exogenous factors such as caloric intake and glucocorticoid use. The study prospectively included 49 children undergoing cardiac surgery. Blood glucose levels, hormonal alterations, and inflammatory responses were investigated before and at the end of surgery, then 12 and 24 h afterward. In general, blood glucose levels were highest at the end of surgery. Hyperglycemia, defined as a glucose level higher than 8.3 mmol/l (>150 mg/dl) was present in 52% of the children at the end of surgery. Spontaneous normalization of blood glucose occurred in 94% of the children within 24 h. During surgery, glucocorticoids were administered to 65% of the children, and this was the main factor associated with hyperglycemia at the end of surgery (determined by univariate analysis of variance). Hyperglycemia disappeared spontaneously without insulin therapy after 12–24 h for the majority of the children. Postoperative morbidity was low in the study group, so the presumed positive effects of glucocorticoids seemed to outweigh the adverse effects of iatrogenic hyperglycemia

Is There a Correlation Between Circulating Levels of Citrulline and Intestinal Dysfunction in the Critically Ill?

Objective: The aim of this study was to assess the correlation between plasma citrulline and Sequential Organ Failure Assessment (SOFA) score, Acute Physiology and Chronic Health Evaluation II (APACHE II) score, survival, inflammation (C-reactive protein [CRP]), inotrope use, serum levels of prealbumin and albumin, and renal failure in the critically ill patient. Methods: This prospective observational singlecenter controlled study included 91 adult patients over a 2-year period. Inclusion criteria were patients staying in the intensive care unit for >48 hours. Patients renal status was categorized as those with a glomerular filtration rate (GFR) >60 mL/min without renal support, a GFR >60 mL/min with renal support, a GFR 36 ?mol/L). The relationship between the recorded parameters and these different cut-off values of plasma citrulline concentrations was analyzed. Results: Ninety-one patients (34% female and 66% male) with a mean (SD) age of 69.3 (11.9) years, a mean (SD) body mass index of 24.8 (5.34) kg/m2, a mean (SD) APACHE II score of 22.4 (7.92), a mean (SD) SOFA score of 8 (4.4), and a mean (SD) plasma citrulline of 21.7 (13.1) μmol/L were enrolled. Only patients with intestinal dysfunction had low plasma citrulline level <15 μmol/L (P = .014). No correlations between serum levels of CRP, albumin, or prealbumin; renal failure; inotrope use; SOFA score; and APACHE II score were found with plasma citrulline level. Conclusion: Low plasma citrulline levels in patients correlate well with intestinal dysfunction. (Nutr Clin Pract. 2012;27:527-532) © 2012 American Society for Parenteral and Enteral Nutrition.SCOPUS: ar.jinfo:eu-repo/semantics/publishe