A novel role for GalNAc-T2 dependent glycosylation in energy homeostasis

OBJECTIVE

GALNT2, encoding polypeptide N-acetylgalactosaminyltransferase 2 (GalNAc-T2), was initially discovered as a regulator of high-density lipoprotein metabolism. GalNAc-T2 is known to exert these effects through post-translational modification, i.e., O-linked glycosylation of secreted proteins with established roles in plasma lipid metabolism. It has recently become clear that loss of GALNT2 in rodents, cattle, nonhuman primates, and humans should be regarded as a novel congenital disorder of glycosylation that affects development and body weight. The role of GALNT2 in metabolic abnormalities other than plasma lipids, including insulin sensitivity and energy homeostasis, is poorly understood.

METHODS

GWAS data from the UK Biobank was used to study variation in the GALNT2 locus beyond changes in high-density lipoprotein metabolism. Experimental data were obtained through studies in Galnt2-/- mice and wild-type littermates on both control and high-fat diet.

RESULTS

First, we uncovered associations between GALNT2 gene variation, adiposity, and body mass index in humans. In mice, we identify the insulin receptor as a novel substrate of GalNAc-T2 and demonstrate that Galnt2-/- mice exhibit decreased adiposity, alterations in insulin signaling and a shift in energy substrate utilization in the inactive phase.

CONCLUSIONS

This study identifies a novel role for GALNT2 in energy homeostasis, and our findings suggest that the local effects of GalNAc-T2 are mediated through posttranslational modification of the insulin receptor.

Biochemical methods to monitor loading and activation of hexameric helicases

Ring-shaped hexameric helicases are an essential class of enzymes that unwind duplex nucleic acids to support a variety of cellular processes. Because of their critical roles in cells, hexameric helicase dysfunction has been linked to DNA damage and genomic instability. Biochemical characterization of hexameric helicase activity and regulation in vitro is necessary for understanding enzyme function and aiding drug discovery efforts. In this chapter, we describe protocols for characterizing mechanisms of helicase loading, activation, and unwinding using the model replicative hexameric DnaB helicase and its cognate DnaC loading factor from E. coli.

Mechanisms of hexameric helicases

Ring-shaped hexameric helicases are essential motor proteins that separate duplex nucleic acid strands for DNA replication, recombination, and transcriptional regulation. Two evolutionarily distinct lineages of these enzymes, predicated on RecA and AAA+ ATPase folds, have been identified and characterized to date. Hexameric helicases couple NTP hydrolysis with conformational changes that move nucleic acid substrates through a central pore in the enzyme. How hexameric helicases productively engage client DNA or RNA segments and use successive rounds of NTPase activity to power translocation and unwinding have been longstanding questions in the field. Recent structural and biophysical findings are beginning to reveal commonalities in NTP hydrolysis and substrate translocation by diverse hexameric helicase families. Here, we review these molecular mechanisms and highlight aspects of their function that are yet to be understood.

The molecular coupling between substrate recognition and ATP turnover in a AAA+ hexameric helicase loader

In many bacteria and eukaryotes, replication fork establishment requires the controlled loading of hexameric, ring-shaped helicases around DNA by AAA+(ATPases Associated with various cellular Activities) ATPases. How loading factors use ATP to control helicase deposition is poorly understood. Here, we dissect how specific ATPase elements of Escherichia coli DnaC, an archetypal loader for the bacterial DnaB helicase, play distinct roles in helicase loading and the activation of DNA unwinding. We have identified a new element, the arginine-coupler, which regulates the switch-like behavior of DnaC to prevent futile ATPase cycling and maintains loader responsiveness to replication restart systems. Our data help explain how the ATPase cycle of a AAA+-family helicase loader is channeled into productive action on its target; comparative studies indicate that elements analogous to the Arg-coupler are present in related, switch-like AAA+ proteins that control replicative helicase loading in eukaryotes, as well as in polymerase clamp loading and certain classes of DNA transposases.

The structure of the colorectal cancer-associated enzyme GalNAc-T12 reveals how nonconserved residues dictate its function

Polypeptide N-acetylgalactosaminyl transferases (GalNAc-Ts) initiate mucin type O-glycosylation by catalyzing the transfer of N-acetylgalactosamine (GalNAc) to Ser or Thr on a protein substrate. Inactive and partially active variants of the isoenzyme GalNAc-T12 are present in subsets of patients with colorectal cancer, and several of these variants alter nonconserved residues with unknown functions. While previous biochemical studies have demonstrated that GalNAc-T12 selects for peptide and glycopeptide substrates through unique interactions with its catalytic and lectin domains, the molecular basis for this distinct substrate selectivity remains elusive. Here we examine the molecular basis of the activity and substrate selectivity of GalNAc-T12. The X-ray crystal structure of GalNAc-T12 in complex with a di-glycosylated peptide substrate reveals how a nonconserved GalNAc binding pocket in the GalNAc-T12 catalytic domain dictates its unique substrate selectivity. In addition, the structure provides insight into how colorectal cancer mutations disrupt the activity of GalNAc-T12 and illustrates how the rules dictating GalNAc-T12 function are distinct from those for other GalNAc-Ts.

Sharing Antimicrobial Reports for Pediatric Stewardship (SHARPS): A Quality Improvement Collaborative

BACKGROUND

Although many children's hospitals have established antimicrobial stewardship programs (ASPs), data-driven benchmarks for optimizing antimicrobial use across centers are lacking. We developed a multicenter quality improvement collaborative focused on sharing data reports and benchmarking antimicrobial use to improve antimicrobial prescribing among hospitalized children.

METHODS

A national antimicrobial stewardship collaborative among children's hospitals, Sharing Antimicrobial Reports for Pediatric Stewardship (SHARPS), was established in 2013. Characteristics of the hospitals and their ASPs were obtained through a standardized survey. Antimicrobial-use data reports were developed on the basis of input from the participating hospitals. Collaborative learning opportunities were provided through monthly webinars and annual meetings.

RESULTS

Since 2013, 36 US hospitals have participated in the SHARPS collaborative. The median full-time equivalent (pharmacist and physician) dedicated to 30 of these ASPs was 0.75 (interquartile range, 0.45-1.4). To date, the collaborative has developed 26 data reports that include benchmarking reports according to specific antimicrobial agents, indications, and clinical service lines. The collaborative has conducted 27 webinars and 3 in-person meetings to highlight the stewardship work being conducted in the hospitals. The data reports and learning opportunities have resulted in approximately 36 distinct stewardship interventions.

CONCLUSION

A pediatric antimicrobial stewardship collaborative has been successful in promoting the development of and innovation among pediatric ASPs. Additional research is needed to determine the impact of these efforts.

Mitral valve prolapse and sudden deafness

To examine the association between MVP and Idiopathic Sudden Sensorineural Hearing loss (ISSNHL). 349 subjects, 86 with ISSNHL and 263 controls underwent a 2D-echocardiography. Patients with ISSNHL had higher rates of MVP (29.1% vs 2.7%, p<0.001), mitral leaflet thickening (15.1% vs 2.3%, p<0.001), mitral regurgitation (16.3% vs 6.5%, p=0.02) and left atrial enlargement (11.6% vs 3.8%, p=0.01). Our results support the hypothesis that MVP could be one of the etiological factors of ISSNHL.

Quality of care in institutionalized deliveries: the paradox of the Dominican Republic

OBJECTIVES

To better understand the paradox in the Dominican Republic of a relatively high maternal mortality ratio despite nearly universal institutionalized deliveries with trained attendants, a rapid assessment using an adaptation of the strategic assessment method was conducted.

METHODS

A multi-disciplinary team reviewed national statistics and hospital records, inventoried facilities, and observed peripartum client-provider interactions at 14 facilities.

RESULTS

The major referral hospitals, where more than 40% of births in the country occur, were overcrowded and understaffed, with inexperienced residents overseeing care provided by medical students, interns and nurses. Uncomplicated labor and deliveries were overmedicalized, while complicated ones were not managed appropriately; emergencies were not dealt with in a timely fashion. In the peripheral hospitals physicians were seldom present and clients were either turned away or delivered by unprepared nursing staff. Providers in the busiest facilities suffered from compassion fatigue, and were demoralized and overworked. In all facilities, quality of care was lacking and the delivery and birthing process was dehumanized.

CONCLUSIONS

Access and availability of institutional delivery alone is not enough to decrease MMR, it is also the quality of emergency obstetric care that saves lives.