Structure and Function of Histone H3 Lysine 9 Methyltransferases and Demethylases

Histone lysine methylation is a dynamic chromatin modification that plays key regulatory roles in gene expression and other genomic functions. Methylation of Lys9 in histone H3 (H3K9) is a prominent modification that has been implicated in diverse processes, including transcriptional silencing, heterochromatin formation, and DNA methylation. In this review, we summarize recent advances in understanding the structure and substrate specificity of the H3K9-specific methyltransferases G9A and GLP and explore current efforts to develop inhibitors of these enzymes. In addition, we discuss the structure and specificity of the recently discovered PHF8 family of histone demethylases that target H3K9 as well as other methylation sites in histones H3 and H4. Finally, we conclude by comparing the H3K9 binding modes displayed by these enzymes and examine the relevance of these studies to their biological functions and to structure-based inhibitor design.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79431/1/254_ftp.pd

The Functions and Importance of CH···O Bonds in SET Domain Methyltransferases.

Methylation is a ubiquitous reaction in biology, particularly with respect to metabolism, signal transduction, and gene regulation. This reaction is most often catalyzed through a convergently evolved SN2 mechanism that utilizes the cofactor S-adenosylmethionine (AdoMet). Despite its importance, little is known of the determinants of this conserved reaction. The following dissertation describes the discovery of one such determinant, unconventional CH•••O hydrogen bonds. A new methodology utilizing NMR spectroscopy is first developed to identify biological CH•••O hydrogen bonds, and applied to the AdoMet methyl group within the active site of model methyltransferase SET7/9. Using a structural survey, the universality of these interactions in the classes of AdoMet-dependent methyltransferases is then demonstrated. The functional importance of CH•••O hydrogen bonds hydrogen within the active site of a model methyltransferase are verified by structural, functional, and dynamic analyses of SET7/9, using a combination of x-ray crystallography, mutagenesis with natural and unnatural amino acids, quantum chemistry calculations, and NMR spin-relaxation experiments. The CH•••O hydrogen bonds are shown to aid in cofactor binding as well as catalysis by stabilizing both the reactant and transition states of methyl transfer, and optimizing the catalytic geometry of the AdoMet methyl group. Together, these studies elucidate a universal mechanism of AdoMet-dependent methyl transfer, providing a molecular framework for this integral biological reaction.PHDBiophysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/97919/1/horowsah_1.pd

Involvement of the right hemisphere in reading comprehension: a DTI study

The Simple View of reading emphasizes the critical role of two factors in normal reading skills: word recognition and reading comprehension. The current study aims to identify the anatomical support for aspects of reading performance that fall within these two components. Fractional anisotropy (FA) values were obtained from Diffusion Tensor images in twenty-one typical adolescents and young adults using the Tract Based Spatial Statistics (TBSS) method. We focused on the Arcuate Fasciculus (AF) and Inferior Longitudinal Fasciculus (ILF) as fiber tracts that connect regions already implicated in the distributed cortical network for reading. Our results demonstrate dissociation between word-level and narrative-level reading skills: the FA values for both left and right ILF were correlated with measures of word reading, while only the left ILF correlated with reading comprehension scores. FA in the AF, however, correlated only with reading comprehension scores, bilaterally. Correlations with the right AF were particularly robust, emphasizing the contribution of the right hemisphere, especially the frontal lobe, to reading comprehension performance on the particular passage comprehension test used in this study. The anatomical dissociation between these reading skills is supported by the Simple View theory and may shed light on why these two skills dissociate in those with reading disorders

Frequent side chain methyl carbon‐oxygen hydrogen bonding in proteins revealed by computational and stereochemical analysis of neutron structures

The propensity of backbone Cα atoms to engage in carbon‐oxygen (CH···O) hydrogen bonding is well‐appreciated in protein structure, but side chain CH···O hydrogen bonding remains largely uncharacterized. The extent to which side chain methyl groups in proteins participate in CH···O hydrogen bonding is examined through a survey of neutron crystal structures, quantum chemistry calculations, and molecular dynamics simulations. Using these approaches, methyl groups were observed to form stabilizing CH···O hydrogen bonds within protein structure that are maintained through protein dynamics and participate in correlated motion. Collectively, these findings illustrate that side chain methyl CH···O hydrogen bonding contributes to the energetics of protein structure and folding. Proteins 2015; 83:403–410. © 2014 Wiley Periodicals, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110709/1/prot24724-sup-0001-suppinfo01.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/110709/2/prot24724.pd

USE OF PERIPHERAL VASOPRESSORS IN EARLY SEPSIS-INDUCED HYPOTENSION ACROSS MICHIGAN HOSPITALS

INTRODUCTION: Recent data suggest it may be safe to administer vasopressors via peripheral IV (PIV), challenging convention that vasopressors must be delivered centrally. Surviving Sepsis Campaign 2021 guidelines suggest using peripheral vasopressors as a bridge to central access. However, little is known about vasopressor initiation in practice. METHODS: Cohort study of patients hospitalized with community-onset sepsis at 12 hospitals in the Hospital Medicine Safety Consortium (HMS) sepsis initiative. HMS is a Collaborative Quality Initiative sponsored by Blue Cross Blue Shield of Michigan. A random sample of adult sepsis hospitalizations between 11/2020-1/2022 were included. Data were abstracted by trained abstractors. We sought to determine how commonly vasopressors were initiated via PIV vs central access across hospitals. HMS-Sepsis is expanding to 69 hospitals. Here we present pilot data; full cohort analysis is in process. RESULTS: of 1,901 patients in the HMS-Sepsis registry at the time of pilot data analysis, 440 (23.1%) had hypotension (defined by mean arterial pressure\u3c 65mmHg, systolic blood pressure\u3c 90mmHg, and/or vasopressor initiation) within 3 hours of hospital arrival. of these, 160 (36.4%) received vasopressors within 6 hours of hospital arrival. Route of initial vasopressor was PIV in 122 (76.3%), central access in 30 (18.8%), midline catheter in 1 (0.6%), oral (ie, midodrine) in 5 (3.1%), and unknown in 2 (1.3%). Across all hospitals, 50.0% to 91.7% of vasopressor initiation was via PIV (median 83.3%). Among 122 patients with vasopressor initiation via PIV, 66 (54.1%) received a 2nd vasopressor, after a median of 2.8 hrs [IQR 1, 8] from 1st vasopressor. Route of 2nd vasopressor was PIV in 27 (40.9%) and central access in 30 (45.4%). Time from hypotension to vasopressor initiation did not differ between patients receiving initial vasopressor via PIV vs central access (median 1.9 vs 2.1 hrs, p=0.79). Likewise, IV fluids within 6 hrs (median 2.0 vs 2.1L, p=0.78), hospitalization length (median 7 vs 6 days, p=0.31), and inhospital mortality (33.6% vs 40.0%, p=0.51) were similar. CONCLUSIONS: In this 12-hospital cohort, vasopressors were most frequently initiated peripherally. Outcomes were similar between patients in whom vasopressors were initiated via peripheral vs central access

Horizontal Inequalities and Ethnonationalist Civil War: A Global Comparison

Contemporary research on civil war has largely dismissed the role of political and economic grievances, focusing instead on opportunities for conflict. However, these strong claims rest on questionable theoretical and empirical grounds. Whereas scholars have examined primarily the relationship between individual inequality and conflict, we argue that horizontal inequalities between politically relevant ethnic groups and states at large can promote ethnonationalist conflict. Extending the empirical scope to the entire world, this article introduces a new spatial method that combines our newly geocoded data on ethnic groups’ settlement areas with spatial wealth estimates. Based on these methodological advances, we find that, in highly unequal societies, both rich and poor groups fight more often than those groups whose wealth lies closer to the country average. Our results remain robust to a number of alternative sample definitions and specifications.</jats:p

Analytical and Numerical Study of Photocurrent Transients in Organic Polymer Solar Cells

This article is an attempt to provide a self consistent picture, including existence analysis and numerical solution algorithms, of the mathematical problems arising from modeling photocurrent transients in Organic-polymer Solar Cells (OSCs). The mathematical model for OSCs consists of a system of nonlinear diffusion-reaction partial differential equations (PDEs) with electrostatic convection, coupled to a kinetic ordinary differential equation (ODE). We propose a suitable reformulation of the model that allows us to prove the existence of a solution in both stationary and transient conditions and to better highlight the role of exciton dynamics in determining the device turn-on time. For the numerical treatment of the problem, we carry out a temporal semi-discretization using an implicit adaptive method, and the resulting sequence of differential subproblems is linearized using the Newton-Raphson method with inexact evaluation of the Jacobian. Then, we use exponentially fitted finite elements for the spatial discretization, and we carry out a thorough validation of the computational model by extensively investigating the impact of the model parameters on photocurrent transient times.Comment: 20 pages, 11 figure

Utility of ambulatory electrocardiographic monitoring for predicting recurrence of sustained ventricular tachyarrhythmias in patients receiving amiodarone

The prognostic implications of changes in ventricular ectopic activity on serial 24 hour ambulatory electrocardiographic (Holter) recordings were prospectively evaluated in 107 patients with a history of sustained ventricular tachyarrhythmias treated with amiodarone for at least 30 days. Twenty-seven patients (25%) had insufficient ventricular ectopic activity < 10 ventricular premature complexes/h and no repetitive forms) on baseline Holter recordings for serial statistical analysis. In 53 (66%) of the remaining 80 patients, serial 24 hour Holter monitor recordings showed efficacy of treatment, defined as a 75% decrease in ventricular premature complexes, a 95% decrease in ventricular couplets and absence of ventricular tachycardia. During a mean followup period of 14.2 ± 9.9 months, 34 (32%) of the 107 patients had recurrence of a sustained ventricular tachyarrhythmia. Holter recording correctly predicted nine recurrences and correctly identified 37 patients who did not experience a recurrence. Holter efficacy failed to predict recurrence of a sustained ventricular tachyarrhythmia in 16 patients, and 18 patients remained free of recurrence despite failure to achieve Holter efficacy. The positive predictive value of Holter monitoring efficacy was 33% and the negative predictive value was 70%; however, these differences were not statistically significant by chi-square analysis. Similar results were obtained using Holter recordings performed relatively early in therapy (6 weeks and 4 months).Of the 27 patients without significant ventricular ectopic activity on the baseline Holter recording, 9 had an arrhythmia recurrence despite continued infrequent ventricular premature complexes and no repetitive forms on subsequent recordings. The recurrence rate in this group (33%) was similar to the overall recurrence rate.Therefore, among patients taking amiodarone for sustained ventricular tachyarrhythmias: 1) 25% will have insufficient ventricular ectopic activity on 24 hour Holter recordings for serial statistical analysis; and 2) in the remaining 75%, data obtained from serial Holter recordings are not predictive of arrhythmia recurrence

Structural and Functional Characterization of Sulfonium Carbon-Oxygen Hydrogen Bonding in the Deoxyamino Sugar Methyltransferase TyIM1

The N-methyltransferase TylM1 from Streptomyces fradiae catalyzes the final step in the biosynthesis of the deoxyamino sugar mycaminose, a substituent of the antibiotic tylosin. The high-resolution crystal structure of TylM1 bound to the methyl donor S-adenosylmethionine (AdoMet) illustrates a network of carbon-oxygen (CH•••O) hydrogen bonds between the substrate’s sulfonium cation and residues within the active site. These interactions include hydrogen bonds between the methyl and methylene groups of the AdoMet sulfonium cation and the hydroxyl groups of Tyr14 and Ser120 in the enzyme. To examine the functions of these interactions, we generated Tyr14 to phenylalanine (Y14F) and Ser120 to alanine (S120A)mutations to selectively ablate the CH•••O hydrogen bonding to AdoMet. The TylM1 S120A mutant exhibited a modest decrease in the catalytic efficiency relative to wild type (WT) enzyme, whereas the Y14F mutation resulted in an approximately 30-fold decrease in catalytic efficiency. In contrast, site-specific substitution of Tyr14 by the noncanonical amino acid p-aminophenylalanine partially restored activity comparable to the WT enzyme. Correlatively, quantum mechanical calculations of the activation barrier energies of WT TylM1 and the Tyr14 mutants suggest that substitutions which abrogate hydrogen bonding with the AdoMet methyl group impair methyl transfer. Together, these results offer insights into roles of CH•••O hydrogen bonding in modulating the catalytic efficiency of TylM1

Association of Infectious Disease Physician Approval of Peripherally Inserted Central Catheter With Appropriateness and Complications

Importance: Peripherally inserted central catheters (PICCs) are frequently used to deliver intravenous antimicrobial therapy. However, inappropriate PICC use may lead to patient harm. Objective: To evaluate whether infectious disease physician approval prior to PICC placement for intravenous antimicrobials is associated with more appropriate device use and fewer complications. Design, Setting, and Participants: This cohort study of 21 653 PICCs placed for a primary indication of intravenous antimicrobial therapy between January 1, 2015, and July 26, 2019, was conducted in 42 hospitals participating in a quality collaborative across Michigan among hospitalized medical patients. Main Outcomes and Measures: Appropriateness of PICCs was defined according to the Michigan Appropriateness Guide for Intravenous Catheters as a composite measure of (1) single-lumen catheter use, (2) avoiding use of PICCs for 5 days or less, and (3) avoiding use of PICCs for patients with chronic kidney disease (defined as an estimated glomerular filtration rate/min/1.73 m2). Complications related to PICCs included catheter occlusion, deep vein thrombosis, and central line-associated bloodstream infection. The association between infectious disease physician approval, device appropriateness, and catheter complications was assessed using multivariable models, adjusted for patient comorbidities and hospital clustering. Results were expressed as odds ratios with 95% CIs. Results: A total of 21 653 PICCs were placed for intravenous antimicrobials (11 960 PICCs were placed in men [55.2%]; median age, 64.5 years [interquartile range, 53.4-75.4 years]); 10 238 PICCs (47.3%) were approved by an infectious disease physician prior to placement. Compared with PICCs with no documented approval, PICCs with approval by an infectious disease physician were more likely to be appropriately used (72.7% [7446 of 10 238] appropriate with approval vs 45.4% [5180 of 11 415] appropriate without approval; odds ratio, 3.53; 95% CI, 3.29-3.79; P \u3c .001). Furthermore, approval was associated with lower odds of a PICC-related complication (6.5% [665 of 10 238] with approval vs 11.3% [1292 of 11 415] without approval; odds ratio, 0.55; 95% CI, 0.50-0.61). Conclusions and Relevance: This cohort study suggests that, when PICCs were placed for intravenous antimicrobial therapy, infectious disease physician approval of PICC insertion was associated with more appropriate device use and fewer complications. Policies aimed at ensuring infectious disease physician approval prior to PICC placement for antimicrobials may improve patient safety