Expanding pyrimidine diphosphosugar libraries via structure-based nucleotidylyltransferase engineering

In vitro "glycorandomization" is a chemoenzymatic approach for generating diverse libraries of glycosylated biomolecules based on natural product scaffolds. This technology makes use of engineered variants of specific enzymes affecting metabolite glycosylation, particularly nucleotidylyltransferases and glycosyltransferases. To expand the repertoire of UDP/dTDP sugars readily available for glycorandomization, we now report a structure-based engineering approach to increase the diversity of alpha-d-hexopyranosyl phosphates accepted by Salmonella enterica LT2 alpha-d-glucopyranosyl phosphate thymidylyltransferase (E(p)). This article highlights the design rationale, determined substrate specificity, and structural elucidation of three "designed" mutations, illustrating both the success and unexpected outcomes from this type of approach. In addition, a single amino acid substitution in the substrate-binding pocket (L89T) was found to significantly increase the set of alpha-d-hexopyranosyl phosphates accepted by E(p) to include alpha-d-allo-, alpha-d-altro-, and alpha-d-talopyranosyl phosphate. In aggregate, our results provide valuable blueprints for altering nucleotidylyltransferase specificity by design, which is the first step toward in vitro glycorandomization.     

Serum sodium predicts mortality in patients listed for liver transplantation

With the implementation of the model for end-stage liver disease (MELD), refractory ascites, a known predictor of mortality in cirrhosis, was removed as a criterion for liver allocation. Because ascites is associated with low serum sodium, we evaluated serum sodium as an independent predictor of mortality in patients with cirrhosis who were listed for liver transplantation and whether the addition of serum sodium to MELD was superior to MELD alone. This is a single-center retrospective cohort of all adult patients with cirrhosis listed for transplantation from February 27, 2002, to December 26, 2003. Listing laboratories were those nearest the listing date +/-2 months. Of the 513 patients meeting inclusion criteria, 341 were still listed, while 172 were removed from the list (105 for transplantation, 56 for death, 11 for other reasons). The median serum sodium and MELD scores were 137 mEq/L (range, 110-155) and 15 (range, 6-51), respectively, at listing. Median follow-up was 201 (range, 1-662) days. The risk of death with serum sodium <126 mEq/L at listing or while listed was increased, with hazard ratios of 7.8 (P < .001) and 6.3 (P < .001), respectively, and the association was independent of MELD. The c-statistics of receiver operating characteristic curves for predicting mortality at 3 months based upon listing MELD with and without listing serum sodium were 0.883 and 0.897, respectively, and at 6 months were 0.871 and 0.905, respectively. In conclusion, serum sodium <126 mEq/L at listing or while listed for transplantation is a strong independent predictor of mortality. Addition of serum sodium to MELD increases the ability to predict 3- and 6-month mortality in patients with cirrhosis.     

Centromere identity is specified by a single centromeric nucleosome in budding yeast

Chromosome segregation ensures that DNA is equally divided between daughter cells during each round of cell division. The centromere (CEN) is the specific locus on each chromosome that directs formation of the kinetochore, the multiprotein complex that interacts with the spindle microtubules to promote proper chromosomal alignment and segregation during mitosis. CENs are organized into a specialized chromatin structure due to the incorporation of an essential CEN-specific histone H3 variant (CenH3) in the centromeric nucleosomes of all eukaryotes. Consistent with its essential role at the CEN, the loss or up-regulation of CenH3 results in mitotic defects. Despite the requirement for CenH3 in CEN function, it is unclear how CenH3 nucleosomes structurally organize centromeric DNA to promote formation of the kinetochore. To address this issue, we developed a modified chromatin immunoprecipitation approach to analyze the number and position of CenH3 nucleosomes at the budding yeast CEN. Using this technique, we show that yeast CENs have a single CenH3 nucleosome positioned over the CEN-determining elements. Therefore, a single CenH3 nucleosome forms the minimal unit of centromeric chromatin necessary for kinetochore assembly and proper chromosome segregation.     

A pilot study of atomoxetine in young children with attention-deficit/hyperactivity disorder

OBJECTIVE: The purpose of this study was to assess the effectiveness and tolerability of atomoxetine during acute treatment of attention-deficit/hyperactivity disorder (ADHD) in 5 and 6 year olds. METHOD: Twenty two children (male n = 19, 86%) with ADHD were treated with atomoxetine for 8 weeks in a three-site, open-label pilot study. Dosing was flexible, with titration to a maximum of 1.8 mg/kg per day. Parent education on behavior management was provided as part of each pharmacotherapy visit. RESULTS: Subjects demonstrated a mean decrease of 20.68 points (SD = 12.80, p < 0.001)) on the ADHD Rating Scale-IV (ADHD-IV-RS) total score, 10.18 (SD = 7.48, p < 0.001) on the inattentive subscale and 10.50 (SD = 7.04, p < 0.001) on the hyperactive/impulsive subscale. Clinical Global Impression-Severity (CGI-S) was improved in 82% of the children (95% CI, 66-98%) and Children's Global Assessment (CGAS) scores improved 18.91 points on average (SD = 12.20, p < 0.001). The mean final dose of atomoxetine was 1.25 mg/kg per day (SD = 0.35 mg/kg per day). Mood lability was the most commonly reported adverse event (n = 12, 54.5%). Eleven subjects (50%) reported decreased appetite and a mean weight loss of 1.04 kg (SD = 0.80 kg) (p < 0.001) was observed for the group. Vital sign changes were mild and not clinically significant. There were no discontinuations due to adverse events or lack of efficacy. CONCLUSION: Atomoxetine was generally effective for reducing core ADHD symptoms in the 5 and 6 year olds in this open-label study.     

Retransplantation for hepatitis C: results of a U.S. multicenter retransplant study.

It is widely perceived that outcomes are relatively poor following retransplantation (reTX) for recurrent of hepatitis C virus (HCV) infection. Transplant centers debate the utility of offering another liver to these patients. A U.S. study group was formed to retrospectively compare survival after reTX in patients with recurrent HCV (histologically proven) and those transplanted for other indications greater than 90 days after first transplantation, from 1996 to 2004. Patients were divided into 3 groups; group 1: HCV reTX (n = 43), group 2: non-HCV reTX (n = 73), and group 3: recurrent HCV but no reTX (n = 156). They were predominantly male, Caucasian, with mean age of 47.2 yr. The commonest indications for non-HCV reTX were chronic rejection (36%), hepatic artery thrombosis (31%) and recurrent primary sclerosing cholangitis (17%). Duration of hospitalization, number of intensive care unit (ICU) days, and time interval from listing to transplantation or reTX were similar between reTX groups. The 1-yr and 3-yr survival rates after reTX were also similar for HCV reTX and non-HCV reTX groups (1 yr, 69% vs. 73%; 3 yr, 49% vs. 55%). Model for End-Stage Liver Disease (MELD) scores were not predictive of survival from reTX. However, with a MELD score of >30 in the non HCV group, survival was <50%. In the recurrent HCV not undergoing reTX group, 30% were reevaluated for reTX but only 15% were listed for reTX and the 3-yr survival was 47%. The most common reasons for not listing for reTX were recurrent HCV within 6 months (22%), fibrosing cholestatic hepatitis (19%), and renal dysfunction (9%). In conclusion, patients retransplanted for recurrent HCV had similar 1-yr and 3-yr survival when compared to patients undergoing reTX for other indications. MELD scores were not predictive of post-reTX survival. Survival was <50% in the non-HCV reTx group with MELD score of >30. Many patients with recurrent HCV are not considered for reTX and die from recurrent disease.     

Direct assignment of vitamin K1 as the secondary acceptor A1 in photosystem I

The characteristic electron spin polarized electron paramagnetic resonance (ESP EPR) signal observed in photosystem I (PSI) has been previously assigned to a radical pair composed of the oxidized primary donor and a reduced vitamin K1. Under conditions in which Bottin, H. & Setif, P. [(1991), Biochim. Biophys. Acta 105, 331-336] proposed that A1 is doubly reduced, the ESP EPR signal was not observed. Therefore, the ESP EPR signal can be directly attributed to A-1, and vitamin K1 can be assigned as this PSI acceptor. The ESP EPR signal was partially restored by removal of the chemical reductants.