Outcomes and risk factors for mortality in clostridioides difficile infection in patients with NAFLD and NASH.

INTRODUCTION AND OBJECTIVES: Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease worldwide and can progress to non-alcoholic steatohepatitis (NASH) and, ultimately, cirrhosis. Clostridioides difficile is the most common nosocomial cause of diarrhea and is associated with worse clinical outcomes in other liver diseases, including cirrhosis, but has not been extensively evaluated in concomitant NAFLD/NASH. MATERIALS AND METHODS: We conducted a retrospective cohort study using the National Inpatient Sample database from 2015 to 2017. Patients with a diagnosis of CDI, NAFLD, and NASH were identified using International Classification of Diseases (Tenth Revision) codes. The outcomes of our study include length of stay, hospitalization cost, mortality, and predictors of mortality. RESULTS: The CDI and NASH cohort had a higher degree of comorbidity burden and prevalence of peptic ulcer disease, congestive heart failure, diabetes mellitus, and cirrhosis. Patients with NASH and CDI had a significantly higher mortality rate compared to the CDI only cohort (mortality, 7.11 % vs. 6.36 %; P = 0.042). Patients with CDI and NASH were at increased risk for liver-related complications, acute kidney injury, and septic shock (P < 0.001) compared to patients with CDI only. Older age, intestinal complications, pneumonia, sepsis and septic shock, and liver failure conferred an increased risk of mortality among the CDI and NASH cohort. CONCLUSIONS: Patients with NASH had a higher rate of liver-related complications, progression to septic shock, and mortality rate following CDI infection compared to the CDI only cohort.

Congenital Riedel's lobe of the liver: A case report.

Riedel's lobe of the liver is a rare anatomical variant often incidentally found on imaging or through the presence of hepatomegaly on physical examination. While patients are usually asymptomatic, the presentation of this condition can vary, ranging from nonspecific symptoms to more severe issues such as torsion, obstruction, rupture, and bleeding. We present a case of a patient with asymptomatic hepatomegaly who was incidentally found to have Riedel's lobe of the liver, accompanied by an elevated IgG mitochondrial antibody. The range of symptoms associated with this rare anatomical variation underscores its importance in diagnosis and surveillance within this patient population.

Increased frequency of hepatic steatosis and fibrosis in patients with gout detected by transient elastography.

OBJECTIVES: It has been suggested that gout is associated with non-alcoholic fatty liver disease (NAFLD). Our aim was to assess NAFLD in gout patients using the validated non-invasive imaging technique, transient elastography (FibroScan). METHODS: FibroScans in consecutive gout patients in a single centre from 11/1/2016 to 11/1/2021 and reviewed retrospectively. FibroScan results include the E- score (kPA), measuring liver stiffness, and controlled attenuation parameter (CAP) score (dB/m), assessing steatosis. In addition, a FIB-4 fibrosis score was calculated. RESULTS: 47 gout patients (7 females, 14.9%; 40 males, 85.1%) underwent FibroScans. The mean age was 59.8 years, the mean body mass index (BMI) was 30.95 kg/m2, and gout duration 0-49 years. Tophi were present in 11 (26.2%). Comorbidities included dyslipidaemia (86.7%), diabetes mellitus (31.1%), known liver disease (33.3%), current alcohol consumption (46.8%), ALT or AST elevations (54.4%), and hyperuricaemia (53.7%). FibroScan results revealed hepatic steatosis (CAP >238 dB/m) in 40 (85.1%) and were significantly associated with BMI (r=0.53, p=0.0001) but not age, serum urate (SU), glucose, triglycerides, ALT, AST. FibroScan also revealed fibrosis (E score >7) in 9 (19.1%); severe fibrosis (cirrhosis) in 8. Fibrosis was significantly associated with age (p=0.03) and known liver disease (p=0.003) but not BMI, SU, or comorbidities. The FIB-4 score was significantly associated with the fibrosis score (r2=0.24, p=0.0009) but not with CAP, ALT, or AST. CONCLUSIONS: Despite not being associated with common gout comorbidities, fatty liver and liver fibrosis were common in this gout cohort, suggesting FibroScan screening in gout patients to assess NAFLD, irrespective of serum transaminase levels.

Early-Onset Colorectal Cancer: Prevalence, Risk Factors, and Clinical Features Among Commercially Insured Adults in the United States.

BACKGROUND:  The incidence of colorectal cancer (CRC) in patients younger than 50 has been rising over the last several decades, accounting for up to 25% of total cases. Despite the screening age recently being lowered to 45, a significant proportion of cases would still arise at younger ages prior to screening. Nonfamilial early-onset CRC remains a particular concern. Identification of risk factors and clinical features in this age group is needed to improve detection. METHODS: In this retrospective cohort analysis using claims data from the Truven Health MarketScan® Commercial Claims insurance database from 2007 to 2017, patients were identified with colon and rectal cancer, compared across three age groups (ages 18-40, 40-50, and >50), and analyzed for risk factors and clinical features. RESULTS: Female sex was more prevalent in the younger age group compared to age >50 (54% and 51.9% vs. 49.6%), with little change noted between rectal cancer age groups by sex. A higher percentage of younger patients were in the obese age groups compared with older groups for colon cancer, particularly the morbidly obese with BMI >40 (24.94%, 25.75%, and 21.34% in the three age groups). Abdominal pain was a common presenting symptom identified in the age groups <50 compared with age >50 (25% and 19% vs. 14%), along with hematochezia, weight loss, and anemia. CONCLUSIONS: Morbid obesity and female sex may be important risk factors among patients with early-onset CRC. The presence of abdominal pain was more common among the early-onset CRC cohort.

Inflammatory pseudotumors in the liver associated with influenza: A case report.

BACKGROUND: Inflammatory pseudotumor (IPT) is a rare and benign lesion that mimics malignancy and can develop in any part of the body. The pathophysiology and etiology of these quasineoplastic lesions remain unclear. CASE SUMMARY: We report a case of a 65-year-old male who presented with fevers, night sweats, and unintentional weight loss following an influenza infection and was found to have multiple hepatic IPT's following an extensive work up. CONCLUSION: Our case highlights the importance of considering hepatic IPT's in the differential in a patient who presents with symptoms and imaging findings mimicking malignancy shortly following a viral infection.

Demographics and Outcomes Related to Wilson's Disease Patients: A Nationwide Inpatient Cohort Study.

Background and objective Wilson's disease (WD) is a rare autosomal recessive disease caused by mutations in the ATP7B gene, leading to impairment in copper excretion and subsequent accumulation primarily in the liver and brain. There is scarce data in the literature on the outcomes and cost burden of WD. In light of this, we aimed to assess outcomes, mortality rates, and costs associated with WD patients and their management in the United States (US). Methods We conducted a retrospective cohort study based on data in the National Inpatient Sample (NIS) database from 2007 to 2017. A total of 17,713 patients with a diagnosis of WD were identified using the International Classification of Diseases, Ninth or Tenth Revision (ICD-9/10) codes. Bivariate analyses were performed using t-tests for continuous variables and Pearson's chi-square tests for categorical variables, where two-sided p-values <0.05 were considered statistically significant. Results The majority of the 17,713 identified patients were female. The mean age of the WD cohort was 49 years. WD patients had a higher prevalence of Kayser-Fleischer rings, neuropsychiatric symptoms, and liver-related complications including acute hepatitis, liver failure, portal hypertension, and cirrhosis. Peptic ulcer disease, connective tissue disease, and hemolytic anemia were significantly more common in the WD cohort. Compared to the non-WD cohort, the WD cohort had a significantly higher mortality rate, longer length of stay (LOS), and increased hospitalization costs (p<0.0001). A higher proportion of patients who had undergone orthotopic liver transplantation (OLTx) were in the 18-34 and 35-44-year-old subgroups. On the contrary, the highest proportion of patients with WD who had not undergone OLTx were in the 55-89-year-old subgroup. WD patients who had undergone OLTx had a lower degree of comorbidities, decreased mortality rate, and shorter LOS (all p<0.0001) compared to WD patients who had not undergone OLTx. Conclusion Based on our findings, patients with WD had a higher LOS, mean hospitalization costs, and mortality rate compared to the non-WD cohort. Mortality rate and LOS were significantly lower in WD patients who had undergone OLTx.

Cryo-EM structure determination of small therapeutic protein targets at 3 Å-resolution using a rigid imaging scaffold.

Cryoelectron microscopy (Cryo-EM) has enabled structural determination of proteins larger than about 50 kDa, including many intractable by any other method, but it has largely failed for smaller proteins. Here, we obtain structures of small proteins by binding them to a rigid molecular scaffold based on a designed protein cage, revealing atomic details at resolutions reaching 2.9 Å. We apply this system to the key cancer signaling protein KRAS (19 kDa in size), obtaining four structures of oncogenic mutational variants by cryo-EM. Importantly, a structure for the key G12C mutant bound to an inhibitor drug (AMG510) reveals significant conformational differences compared to prior data in the crystalline state. The findings highlight the promise of cryo-EM scaffolds for advancing the design of drug molecules against small therapeutic protein targets in cancer and other human diseases.

Surgery in Nonalcoholic Cirrhosis: Clinical Outcomes, Healthcare Utilization, and Cost Analysis.

BACKGROUND: Patients with cirrhosis are at increased risk of complications following surgery due to multiple factors, including portal hypertension and alterations in hemostasis. Improvements in perioperative management as well as risk stratification scores have helped improve outcomes, but gaps remain in our understanding of the cost and morbidity of cirrhotic patients who undergo surgery. METHODS: We conducted a case-control study using the IBM Electronic Health Record (EHR) MarketScan Commercial Claims (MSCC) database from January 1, 2007 to December 31, 2017. Nonalcoholic cirrhotic patients who underwent surgery were identified based on International Classification of Diseases, Ninth Revision (ICD-9)/Tenth Revision (ICD-10) codes for multiple surgical categories and matched with controls with cirrhosis who did not undergo surgery in this time period. A total of 115,512 patients were identified with cirrhosis, of whom 19,542 (16.92%) had surgery. Medical history and comorbidities were compiled, and outcomes in the six-month period following surgery were analyzed between matched groups. A cost analysis was performed based on claims data. RESULTS: Nonalcoholic cirrhotic patients who underwent surgery had a higher comorbidity index at baseline compared with controls (1.34 vs. 0.88, P<0.0001). Mortality was increased in the surgery group (4.68% vs. 2.38%, P<0.001) in the follow-up period. The surgical cohort had higher rates of adverse hepatic outcomes, including hepatic encephalopathy (5.00% vs. 2.50%, P<0.0001), spontaneous bacterial peritonitis (0.64% vs. 0.25%, P<0.001), and higher rates of septic shock (0.66% vs. 0.14%, P<0.001), intracerebral hemorrhage (0.49% vs. 0.04%, P<0.001), and acute hypoxemic respiratory failure (7.02% vs. 2.31%, P<0.001). Healthcare utilization analysis revealed increased total claims per patient in the surgical cohort (38.11 vs. 28.64, P<0.0001), higher inpatient admissions (6.05 vs. 2.35, P<0.0001), more outpatient visits (19.72 vs. 15.23, P<0.0001), and prescription claims per patient (11.76 vs. 10.61, P<0.0001) in the postsurgical period. The likelihood of at least one inpatient stay was higher in the surgical cohort (51.63% vs. 22.32%, P<0.0001), and inpatient stays were longer (4.99 days vs. 2.09 days, P<0.0001). The total cost of health services was significantly increased per patient in the postoperative period for patients undergoing surgery ($58,246 vs. $26,842, P<0.0001), largely due to increased inpatient costs ($34,446 vs. $10,789, P<0.0001). CONCLUSION: Nonalcoholic cirrhotics undergoing surgery experienced worse outcomes with respect to adverse hepatic events and complications, including septic shock and intracerebral hemorrhage. Claims and cost analysis showed a significant increase in health expenditure in the surgical group, largely due to the cost of more frequent and longer inpatient admissions.

Outcomes, Mortality, and Cost Burden of Acute Kidney Injury and Hepatorenal Syndrome in Patients with Cirrhosis.

BACKGROUND AND AIMS: Cirrhosis is associated with an increased risk of acute kidney injury (AKI) and hepatorenal syndrome (HRS). Healthcare utilization and cost burden of AKI and HRS in cirrhosis is unknown. We aimed to analyze the health care use and cost burden associated with AKI and HRS in patients with cirrhosis in the United States by using real-world claims data. METHODS: We conducted a case-control study using the Truven Health MarketScan Commercial Claims databases from 2007-2017. A total of 34,398 patients with cirrhosis with or without AKI and 4,364 patients with cirrhosis with or without HRS were identified using International Classification of Diseases, Ninth or Tenth Revision, codes and matched 1:1 by sociodemographic characteristics and comorbidities using propensity scores. Total and service-specific were quantified for the 12-months following versus the 12-months before the first date of AKI or HRS diagnosis and over 12-months following a randomly selected date for cirrhosis controls to capture entire disease burdens. RESULTS: The AKI and HRS group had a higher number of comorbidities and were associated with higher rates of readmission and mortality. The AKI and HRS groups had a significantly higher prevalence of ascites, spontaneous bacterial peritonitis (SBP), encephalopathy, gastrointestinal bleeding, septic shock, pulmonary edema, and respiratory failure. Compared to patients with cirrhosis only, AKI was associated with higher number of claims per person (AKI vs. cirrhosis only, 60.30 vs. 47.09; p<0.0001) and total annual median health care costs (AKI vs. cirrhosis only, $46,150 vs. $26,340; p<0.0001). Compared to patients with cirrhosis only, the HRS cohort was associated with a higher number of claims per person (HRS vs. cirrhosis only, 44.96 vs. 43.50; p<0.0009) and total annual median health care costs (HRS vs. cirrhosis only, $34,912 vs. $23,354; p<0.0001). Inpatient costs were higher than the control cohort for AKI (AKI vs. cirrhosis only, $72,720 vs. $29,111; p<0.0001) and HRS (HRS vs. cirrhosis only, $ 98,246 vs. $27,503; p<0.0001). Compared to the control cohort, AKI and HRS had a higher rate of inpatient admission, mean number of inpatient admissions, and mean total length of stay. CONCLUSIONS: AKI and HRS are associated with higher health care utilization and cost burden compared to cirrhosis alone, highlighting the importance for improved screening and treatment modalities.

Reduction in Gastrointestinal Cancers in Cirrhotic Patients Receiving Rifaximin vs Lactulose Only Therapy for Hepatic Encephalopathy.

Background Rifaximin and/or lactulose therapy is widely used in cirrhotic patients for the prevention and treatment of hepatic encephalopathy. The incidence of gastrointestinal cancers in these patients on lactulose, rifaximin, and/or combination therapy is unknown. We investigated the possible effect of lactulose and rifaximin on cancer risk in patients with cirrhosis using the MarketScan database. Methods A retrospective cohort study was conducted using the Truven Health MarketScan Commercial Claims databases from 2007-2017. An index date was defined for each participant as the earliest date of cirrhosis diagnosis. A baseline period for each participant was defined as the 12 months prior to the first medication date while the study follow-up period represented the period from the initiation of the medication to its cessation. ANOVA was used to compare all continuous measures of age and duration of medication. Wald Chi-square tests were performed to test the associations between the study groups. Results A total of 12,409 patients were included in our study. The rifaximin only cohort had the greatest reduction in risk of developing colon cancer, esophageal cancer, and stomach cancer compared to the other groups. Rifaximin reduced the risk of colon cancer and esophageal cancer by 59.42% and 70.37%, respectively, compared to patients taking lactulose only. Patients in the lactulose plus rifaximin cohort had the highest rate of development of pancreatic cancer (lactulose plus rifaximin vs rifaximin only vs lactulose only, 0.45% vs 0.24% vs 0.21%; P < 0.0001) and liver and intrahepatic bile duct cancers (11.73% vs 5.84% vs 5.49%; P < 0.0001). Conclusion Colon, esophageal, and gastric cancers had a marked incidence reduction in the rifaximin only cohort compared to the other cohorts studied.

EUS of a submucosal lesion at the appendiceal orifice using a double-balloon endoluminal intervention platform.

Video 1Video demonstrating the use of a DEIP to facilitate both radial and linear EUS in the proximal colon.

Nonalcoholic Fatty Liver Disease in Lean/Nonobese and Obese Individuals: A Comprehensive Review on Prevalence, Pathogenesis, Clinical Outcomes, and Treatment.

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease worldwide, with an estimated prevalence of 25% globally. NAFLD is closely associated with metabolic syndrome, which are both becoming increasingly more common with increasing rates of insulin resistance, dyslipidemia, and hypertension. Although NAFLD is strongly associated with obesity, lean or nonobese NAFLD is a relatively new phenotype and occurs in patients without increased waist circumference and with or without visceral fat. Currently, there is limited literature comparing and illustrating the differences between lean/nonobese and obese NAFLD patients with regard to risk factors, pathophysiology, and clinical outcomes. In this review, we aim to define and further delineate different phenotypes of NAFLD and present a comprehensive review on the prevalence, incidence, risk factors, genetic predisposition, and pathophysiology. Furthermore, we discuss and compare the clinical outcomes, such as insulin resistance, dyslipidemia, hypertension, coronary artery disease, mortality, and progression to nonalcoholic steatohepatitis, among lean/nonobese and obese NAFLD patients. Finally, we summarize the most up to date current management of NAFLD, including lifestyle interventions, pharmacologic therapies, and surgical options.

Ubiquitin variants potently inhibit SARS-CoV-2 PLpro and viral replication via a novel site distal to the protease active site.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has made it clear that combating coronavirus outbreaks benefits from a combination of vaccines and therapeutics. A promising drug target common to all coronaviruses-including SARS-CoV, MERS-CoV, and SARS-CoV-2-is the papain-like protease (PLpro). PLpro cleaves part of the viral replicase polyproteins into non-structural protein subunits, which are essential to the viral replication cycle. Additionally, PLpro can cleave both ubiquitin and the ubiquitin-like protein ISG15 from host cell substrates as a mechanism to evade innate immune responses during infection. These roles make PLpro an attractive antiviral drug target. Here we demonstrate that ubiquitin variants (UbVs) can be selected from a phage-displayed library and used to specifically and potently block SARS-CoV-2 PLpro activity. A crystal structure of SARS-CoV-2 PLpro in complex with a representative UbV reveals a dimeric UbV bound to PLpro at a site distal to the catalytic site. Yet, the UbV inhibits the essential cleavage activities of the protease in vitro and in cells, and it reduces viral replication in cell culture by almost five orders of magnitude.

Acute liver injury and IgG4-related autoimmune pancreatitis following mRNA-based COVID-19 vaccination.

IgG4-related disease (IgG4-RD) is a fibro-inflammatory disease that can affect multiple organs. Autoimmune pancreatitis type 1 is a manifestation of IgG4-RD and can often mimic tumor-like masses. Autoimmune phenomena following COVID-19 mRNA vaccination are being increasingly reported. Currently, there are no cases in which IgG4-RD involving the hepatobiliary system has been reported following the COVID-19 vaccination. We present the first case of IgG4-RD and AIP type 1 to be associated with the mRNA-based COVID-19 vaccination.

Electrophoretic mobility of individual molecules of alkaline phosphatase.

The electrophoretic mobilities and catalytic rates of individual molecules of bovine intestinal alkaline phosphatase were determined in CHES and borate buffers of identical pH using a capillary electrophoresis based method. Both properties were found to be heterogeneous. In the presence of CHES, the mobility and rate were found to be -1.9 ± 0.2 × 10-9 m2 V-1 s-1 and 9.8 ± 7.4 × 104 min-1 (N = 38), respectively. In the presence of borate, the mobility and rate were found to be -6.9 ± 0.5 × 10-9 m2 V-1 s-1 and 2.0 ± 1.3 × 104 min-1 (N = 41), respectively. The means and variances for both properties were found to differ significantly between the two buffers. The difference in average mobility was attributed to an increase in negative charge caused by borate complexing with the carbohydrate moieties attached to the enzyme. The difference in variance was attributed to heterogeneous complexation with borate due to heterogeneity in the glycosylation. The differences in mean values for the catalytic rate were attributed to the inhibitory effect of borate and the difference in variance may suggest that the KI of this binding may also be heterogeneous.

The Spontaneous Regression of Primary Gastrointestinal Malignancies: An Observational Review.

The spontaneous regression or remission (SR) of cancer, often described as the partial or complete disappearance of a malignant tumor in the absence of all medical treatment and therapy, is a well-documented phenomenon. With efforts ongoing to establish cancer treatments that limit undesirable outcomes and adverse effects, these uncommon occurrences of SR carry significant implications for novel therapies and warrant further investigation. While several case studies have reported instances of SR in gastrointestinal (GI) malignancies, a comprehensive review of previous manifestations of SR in the GI tract remains lacking. The inclusion criteria for the rare phenomenon are also in need of an appropriate update that takes recent scientific advancements and emerging new medical technologies into account. Our analysis of 390 cases of SR in the GI tract focuses primarily on neoplasms of the hepatobiliary system and proposes an updated version of the older inclusion criteria for spontaneous regression.

The endopeptidase of the maize-affecting Marafivirus type member maize rayado fino virus doubles as a deubiquitinase.

Marafiviruses are capable of persistent infection in a range of plants that have importance to the agriculture and biofuel industries. Although the genomes of a few of these viruses have been studied in-depth, the composition and processing of the polyproteins produced from their main ORFs have not. The Marafivirus polyprotein consists of essential proteins that form the viral replicase, as well as structural proteins for virus assembly. It has been proposed that Marafiviruses code for cysteine proteases within their polyproteins, which act as endopeptidases to autocatalytically cleave the polyprotein into functional domains. Furthermore, it has also been suggested that Marafivirus endopeptidases may have deubiquitinating activity, which has been shown to enhance viral replication by downregulating viral protein degradation by the ubiquitin (Ub) proteasomal pathway as well as tampering with cell signaling associated with innate antiviral responses in other positive-sense ssRNA viruses. Here, we provide the first evidence of cysteine proteases from six different Marafiviruses that harbor deubiquitinating activity and reveal intragenus differences toward Ub linkage types. We also examine the structural basis of the endopeptidase/deubiquitinase from the Marafivirus type member, maize rayado fino virus. Structures of the enzyme alone and bound to Ub reveal marked structural rearrangements that occur upon binding of Ub and provide insights into substrate specificity and differences that set it apart from other viral cysteine proteases.

Postoperative opioid-free analgesia in elective bowel resection: Changes over time.

In the pain management evolution, opioid-free analgesia and multimodal analgesia strategies have emerged as feasible in many surgical settings including colorectal surgery. This was a retrospective cohort study including patients having undergone elective bowel resection between February 2012 and June 2018 aiming to evaluate whether there was reduction in opioid use after implementation of opioid-free analgesia in one medical centre. Trend analysis was conducted using Joinpoint regression employing nine-month intervals. The primary outcome for each interval was the proportion of patients receiving postoperative opioid-free analgesia, defined as forgoing all opioid analgesics after the day of surgery. This study showed a significant increasing trend in opioid-free analgesia in elective bowel resection from 0 to 42.5% over 4.5 years.

Molecular characterization of the RNA-protein complex directing -2/-1 programmed ribosomal frameshifting during arterivirus replicase expression.

Programmed ribosomal frameshifting (PRF) is a mechanism used by arteriviruses like porcine reproductive and respiratory syndrome virus (PRRSV) to generate multiple proteins from overlapping reading frames within its RNA genome. PRRSV employs -1 PRF directed by RNA secondary and tertiary structures within its viral genome (canonical PRF), as well as a noncanonical -1 and -2 PRF that are stimulated by the interactions of PRRSV nonstructural protein 1ß (nsp1ß) and host protein poly(C)-binding protein (PCBP) 1 or 2 with the viral genome. Together, nsp1ß and one of the PCBPs act as transactivators that bind a C-rich motif near the shift site to stimulate -1 and -2 PRF, thereby enabling the ribosome to generate two frameshift products that are implicated in viral immune evasion. How nsp1ß and PCBP associate with the viral RNA genome remains unclear. Here, we describe the purification of the nsp1ß:PCBP2:viral RNA complex on a scale sufficient for structural analysis using small-angle X-ray scattering and stochiometric analysis by analytical ultracentrifugation. The proteins associate with the RNA C-rich motif as a 1:1:1 complex. The monomeric form of nsp1ß within the complex differs from previously reported homodimer identified by X-ray crystallography. Functional analysis of the complex via mutational analysis combined with RNA-binding assays and cell-based frameshifting reporter assays reveal a number of key residues within nsp1ß and PCBP2 that are involved in complex formation and function. Our results suggest that nsp1ß and PCBP2 both interact directly with viral RNA during formation of the complex to coordinate this unusual PRF mechanism.

Structural and mechanistic analysis of a ß-glycoside phosphorylase identified by screening a metagenomic library.

Glycoside phosphorylases have considerable potential as catalysts for the assembly of useful glycans for products ranging from functional foods and prebiotics to novel materials. However, the substrate diversity of currently identified phosphorylases is relatively small, limiting their practical applications. To address this limitation, we developed a high-throughput screening approach using the activated substrate 2,4-dinitrophenyl ß-d-glucoside (DNPGlc) and inorganic phosphate for identifying glycoside phosphorylase activity and used it to screen a large insert metagenomic library. The initial screen, based on release of 2,4-dinitrophenyl from DNPGlc in the presence of phosphate, identified the gene bglP, encoding a retaining ß-glycoside phosphorylase from the CAZy GH3 family. Kinetic and mechanistic analysis of the gene product, BglP, confirmed a double displacement ping-pong mechanism involving a covalent glycosyl-enzyme intermediate. X-ray crystallographic analysis provided insights into the phosphate-binding mode and identified a key glutamine residue in the active site important for substrate recognition. Substituting this glutamine for a serine swapped the substrate specificity from glucoside to N-acetylglucosaminide. In summary, we present a high-throughput screening approach for identifying ß-glycoside phosphorylases, which was robust, simple to implement, and useful in identifying active clones within a metagenomics library. Implementation of this screen enabled discovery of a new glycoside phosphorylase class and has paved the way to devising simple ways in which enzyme specificity can be encoded and swapped, which has implications for biotechnological applications.