Salt-Bridged Peptide Anion Gaseous Structures Enable Efficient Negative Ion Electron Capture Dissociation

We previously discovered that electron attachment to gaseous peptide anions can occur within a relatively narrow electron energy range. The resulting charge-increased radical ions undergo dissociation analogous to conventional cation electron capture/transfer dissociation (ECD/ETD), thus enabling a novel tandem mass spectrometry (MS/MS) technique that we termed negative ion electron capture dissociation (niECD). We proposed that gaseous zwitterionic structures are required for niECD with electron capture either occurring at or being directed by a positively charged site. Here, we further evaluate this zwitterion mechanism by performing niECD of peptides derivatized to alter their ability to form zwitterionic gaseous structures. Introduction of a fixed positive charge tag, a highly basic guanidino group, or a highly acidic sulfonate group to promote zwitterionic structures in singly charged anions, rescued the niECD ability of a peptide refractory to niECD in its unmodified form. We also performed a systematic study of five sets of synthetic peptides with decreasing zwitterion propensity and found that niECD efficiency decreased accordingly, further supporting the zwitterion mechanism. However, traveling-wave ion mobility-mass spectrometry experiments, performed to gain further insight into the gas-phase structures of peptides showing high niECD efficiency, exhibited an inverse correlation between the orientationally averaged collision cross sections and niECD efficiency. These results indicate that compact salt-bridged structures are also a requirement for effective niECD.

Multimodal Preventive Trial for Alzheimer's Disease: MIND-ADmini Pilot Trial Study Design and Progress

Background

Interventions simultaneously targeting multiple risk factors and mechanisms are most likely to be effective in preventing cognitive impairment. This was indicated in the Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability (FINGER) testing a multidomain lifestyle intervention among at-risk individuals. The importance of medical food at the early symptomatic disease stage, prodromal Alzheimer’s disease (AD), was emphasized in the LipiDiDiet trial. The feasibility and effects of multimodal interventions in prodromal AD are unclear.

Objectives

To evaluate the feasibility of an adapted FINGER-based multimodal lifestyle intervention, with or without medical food, among individuals with prodromal AD.

Methods

MIND-ADmini is a multinational proof-of-concept 6-month randomized controlled trial (RCT), with four trial sites (Sweden, Finland, Germany, France). The trial targeted individuals with prodromal AD defined using the International Working Group-1 criteria, and with vascular or lifestyle-related risk factors. The parallel-group RCT includes three arms: 1) multimodal lifestyle intervention (nutritional guidance, exercise, cognitive training, vascular/metabolic risk management and social stimulation); 2) multimodal lifestyle intervention+medical food (Fortasyn Connect); and 3) regular health advice/ care (control group). Primary outcomes are feasibility and adherence. Secondary outcomes are adherence to the individual intervention domains and healthy lifestyle changes.

Results

Screening began on 28 September 2017 and was completed on 21 May 2019. Altogether 93 participants were randomized and enrolled. The intervention proceeded as planned.

Conclusions

For the first time, this pilot trial tests the feasibility and adherence to a multimodal lifestyle intervention, alone or combined with medical food, among individuals with prodromal AD. It can serve as a model for combination therapy trials (non-pharma, nutrition-based and/or pharmacological interventions).

Gas-Phase Hydrogen/Deuterium Scrambling in Negative-Ion Mode Tandem Mass Spectrometry

Hydrogen/deuterium exchange coupled with mass spectrometry (HDX MS) has become a powerful method to characterize protein conformational dynamics. Workflows typically utilize pepsin digestion prior to MS analysis to yield peptide level structural resolution. Tandem mass spectrometry (MS/MS) can potentially facilitate determination of site-specific deuteration to single-residue resolution. However, to be effective, MS/MS activation must minimize the occurrence of gas-phase intramolecular randomization of solution-generated deuterium labels. While significant work has focused on understanding this process in positive-ion mode, little is known about hydrogen/deuterium (H/D) scrambling processes in negative-ion mode. Here, we utilize selectively deuterated model peptides to investigate the extent of intramolecular H/D scrambling upon several negative-ion mode MS/MS techniques, including negative-ion collision-induced dissociation (nCID), electron detachment dissociation (EDD), negative-ion free radical-initiated peptide sequencing (nFRIPS), and negative-ion electron capture dissociation (niECD). H/D scrambling was extensive in deprotonated peptides upon nCID and nFRIPS. In fact, the energetics required to induce dissociation in nCID are sufficient to allow histidine C-2 and C_β hydrogen atoms to participate in the scrambling process. EDD and niECD demonstrated moderate H/D scrambling with niECD being superior in terms of minimizing hydrogen migration, achieving ~ 30% scrambling levels for small c-type fragment ions. We believe the observed scrambling is likely due to activation during ionization and ion transport rather than during the niECD event itself.

Risk profiling based on p16 and HPV DNA more accurately predicts location of disease relapse in patients with oropharyngeal squamous cell carcinoma

BACKGROUND

In the era of precision medicine and HPV-related oropharyngeal squamous cell carcinoma (OPSCC), it is relevant to assess the risk of not only survival, but also the risk of local, regional, or distant treatment failure. The UICC 8th edition uses the surrogate marker p16 to stratify for HPV association but discordance between p16 status and HPV association has been shown. The purpose of this study was to develop a prognostic model to predict the risk of local, regional, and distant metastases and non-cancer-related death for patients with OPSCC, test the prognostic relevance of adding HPV DNA and p16 status, and validate the findings in an independent external dataset.

PATIENTS AND METHODS

Consecutive patients diagnosed with OPSCC and treated with curative radiotherapy with or without cisplatin in eastern Denmark from 2000 to 2014 were included. Characteristics included age, gender, TNM stage, smoking habits, performance status, and HPV status assessed with p16 and HPV DNA. The information was used to develop a prognostic model for first site of failure with four competing events: recurrence in T-, N-, and M-site, and death with no evidence of disease.

RESULTS

Overall 1243 patients were eligible for the analysis. A prognostic model with the four events was developed and externally validated in an independent dataset with a heterogeneously treated patient population from another institution. The individual prognostication from the competing risk analysis is displayed in a user friendly online tool (https://rasmussen.shinyapps.io/OPSCCmodelHPV_p16/). Replacing p16 status with the combined variable HPV/p16 status influenced the HR and patients with HPV-/p16+ had significantly higher HR of M-site recurrence than HPV+/p16+ with a HR = 2.56; CI [1.30; 5.02]; P = 0.006 (P = 0.013 in the validation cohort).

CONCLUSION

Patients with HPV-/p16+ have significantly higher risk of M-site recurrence and could potentially be relevant candidates for clinical trials testing systemic treatments in combination with conventional treatments.

Free Radical Initiated Peptide Sequencing for Direct Site Localization of Sulfation and Phosphorylation with Negative Ion Mode Mass Spectrometry

Tandem mass spectrometry (MS/MS) is the primary method for discovering, identifying, and localizing post-translational modifications (PTMs) in proteins. However, conventional positive ion mode collision induced dissociation (CID)-based MS/MS often fails to yield site-specific information for labile and acidic modifications due to low ionization efficiency in positive ion mode and/or preferential PTM loss. While a number of alternative methods have been developed to address this issue, most require specialized instrumentation or indirect detection. In this work, we present an amine-reactive TEMPO-based free radical initiated peptide sequencing (FRIPS) approach for negative ion mode analysis of phosphorylated and sulfated peptides. FRIPS-based fragmentation generates sequence informative ions for both phosphorylated and sulfated peptides with no significant PTM loss. Furthermore, FRIPS is compared to positive ion mode CID, electron transfer dissociation (ETD), as well as negative ion mode electron capture dissociation (niECD) and CID, both in terms of sequence coverage and fragmentation efficiency for phospho- and sulfo-peptides. Because FRIPS-based fragmentation has no particular instrumentation requirements and shows limited PTM loss, we propose this approach as a promising alternative to current techniques for analysis of labile and acidic PTMs.

Exhaled and nasal nitric oxide in chronic rhinosinusitis patients with nasal polyps in primary care

BACKGROUND

Chronic rhinosinusitis with nasal polyps (CRSwNP) is a common inflammatory disorder associated with lower airway disease. However, only few studies of CRSwNP from outside secondary/tertiary care centres have been published. We recently reported an asthma frequency of 44% and 65% in primary and secondary care patients respectively. Therefore, we hypothesise that inflammation of the lower airways could be present in all CRSwNP patients, even without asthma. Here, we assessed the degree of lower and upper airway inflammation using exhaled and nasal nitric oxide (NO) in primary care CRSwNP patients with and without asthma.

METHODS

Fifty-seven patients who met the EPOS criteria for CRSwNP were prospectively recruited from primary care ear, nose and throat clinics. Nasal endoscopy was performed by an ear, nose and throat specialist upon enrolment. Additionally, 30 healthy controls were enrolled. Expiratory and nasal NO measurements and thorough pulmonary evaluation were performed. Pulmonary disease was diagnosed by a respiratory physician.

RESULTS

Fifty-nine percent of CRSwNP patients with asthma showed elevated expiratory NO; the same was seen in 29% of non-asthmatic CRSwNP patients. Compared with controls, a high level of exhaled NO was significantly more prevalent in CRSwNP irrespective of asthma-status. Nasal NO was significantly lower in patients with CRSwNP compared with controls.

CONCLUSION

Subclinical eosinophilic lower airway inflammation is common in CRSwNP in the primary sector, even in the absence of asthma.

Exhaled and nasal nitric oxide in chronic rhinosinusitis patients with nasal polyps in primary care

BACKGROUND

Chronic rhinosinusitis with nasal polyps (CRSwNP) is a common inflammatory disorder associated with lower airway disease. However, only few studies of CRSwNP from outside secondary/tertiary care centres have been published. We recently reported an asthma frequency of 44% and 65% in primary and secondary care patients respectively. Therefore, we hypothesise that inflammation of the lower airways could be present in all CRSwNP patients, even without asthma. Here, we assessed the degree of lower and upper airway inflammation using exhaled and nasal nitric oxide (NO) in primary care CRSwNP patients with and without asthma.

METHODS

Fifty-seven patients who met the EPOS criteria for CRSwNP were prospectively recruited from primary care ear, nose and throat clinics. Nasal endoscopy was performed by an ear, nose and throat specialist upon enrolment. Additionally, 30 healthy controls were enrolled. Expiratory and nasal NO measurements and thorough pulmonary evaluation were performed. Pulmonary disease was diagnosed by a respiratory physician.

RESULTS

Fifty-nine percent of CRSwNP patients with asthma showed elevated expiratory NO; the same was seen in 29% of non-asthmatic CRSwNP patients. Compared with controls, a high level of exhaled NO was significantly more prevalent in CRSwNP irrespective of asthma-status. Nasal NO was significantly lower in patients with CRSwNP compared with controls.

CONCLUSION

Subclinical eosinophilic lower airway inflammation is common in CRSwNP in the primary sector, even in the absence of asthma.

The risk of osteoporosis in oral steroid treatment for nasal polyposis: a systematic review

BACKGROUND

Systemic glucocorticoids are often used in the treatment of chronic rhinosinusitis with nasal polyps (CRSwNP), and osteoporosis is a well-known complication to steroid treatment, associated with significant morbidity. Nevertheless, the burden of steroid induced osteoporosis is unknown in patients with CRSwNP. We aimed to assess the risk of acquiring osteoporosis caused by oral steroids in patients with CRSwNP, and provide recommendations on future research and guidelines.

METHODOLOGY

Cochrane Review Database, EMBASE, Ovid Medline, and PubMed were searched for studies including adult patients with CRSwNP treated with oral steroids. Outcomes were Bone Mineral Density (BMD) and prevalence of fractures in relation to dose and duration of oral steroids. In addition, we reviewed general guidelines for treatment with oral steroids.

RESULTS

We identified two studies (n=243) that met the inclusion criteria. Doses and durations of oral steroids were over 5 mg/day for more than 3 months and 1 mg/kg body weight/day for 6 to 10 days for 4 or more courses/year. The prevalence of low bone mass was 39% and 61%, respectively. It was not possible to quantify the overall risk of osteoporosis induced by oral steroids from the studies. No studies evaluated prevalence of fracture.

CONCLUSIONS

Registry studies and randomized controlled trials would be needed to assess the risk of osteoporosis in CRSwNP patients and future guidelines should include recommendations regarding preventive treatment and recommendations on doses and durations of oral steroids.

Corona Discharge Suppression in Negative Ion Mode Nanoelectrospray Ionization via Trifluoroethanol Addition

Negative ion mode nanoelectrospray ionization (nESI) is often utilized to analyze acidic compounds, from small molecules to proteins, with mass spectrometry (MS). Under high aqueous solvent conditions, corona discharge is commonly observed at emitter tips, resulting in low ion abundances and reduced nESI needle lifetimes. We have successfully reduced corona discharge in negative ion mode by trace addition of trifluoroethanol (TFE) to aqueous samples. The addition of as little as 0.2% TFE increases aqueous spray stability not only in nESI direct infusion, but also in nanoflow liquid chromatography (nLC)/MS experiments. Negative ion mode spray stability with 0.2% TFE is approximately 6× higher than for strictly aqueous samples. Upon addition of 0.2% TFE to the mobile phase of nLC/MS experiments, tryptic peptide identifications increased from 93 to 111 peptides, resulting in an average protein sequence coverage increase of 18%.

The risk of osteoporosis in oral steroid treatment for nasal polyposis: a systematic review

BACKGROUND

Systemic glucocorticoids are often used in the treatment of chronic rhinosinusitis with nasal polyps (CRSwNP), and osteoporosis is a well-known complication to steroid treatment, associated with significant morbidity. Nevertheless, the burden of steroid induced osteoporosis is unknown in patients with CRSwNP. We aimed to assess the risk of acquiring osteoporosis caused by oral steroids in patients with CRSwNP, and provide recommendations on future research and guidelines.

METHODOLOGY

Cochrane Review Database, EMBASE, Ovid Medline, and PubMed were searched for studies including adult patients with CRSwNP treated with oral steroids. Outcomes were Bone Mineral Density (BMD) and prevalence of fractures in relation to dose and duration of oral steroids. In addition, we reviewed general guidelines for treatment with oral steroids.

RESULTS

We identified two studies (n=243) that met the inclusion criteria. Doses and durations of oral steroids were over 5 mg/day for more than 3 months and 1 mg/kg body weight/day for 6 to 10 days for 4 or more courses/year. The prevalence of low bone mass was 39% and 61%, respectively. It was not possible to quantify the overall risk of osteoporosis induced by oral steroids from the studies. No studies evaluated prevalence of fracture.

CONCLUSIONS

Registry studies and randomized controlled trials would be needed to assess the risk of osteoporosis in CRSwNP patients and future guidelines should include recommendations regarding preventive treatment and recommendations on doses and durations of oral steroids.

Targeted Annotation of S-Sulfonylated Peptides by Selective Infrared Multiphoton Dissociation Mass Spectrometry

Protein S-sulfinylation (R-SO₂^-) and S-sulfonylation (R-SO₃^-) are irreversible oxidative post-translational modifications of cysteine residues. Greater than 5% of cysteines are reported to occupy these higher oxidation states, which effectively inactivate the corresponding thiols and alter the electronic and physical properties of modified proteins. Such higher oxidation states are reached after excessive exposure to cellular oxidants, and accumulate across different disease states. Despite widespread and functionally relevant cysteine oxidation across the proteome, there are currently no robust methods to profile higher order cysteine oxidation. Traditional data-dependent liquid chromatography/tandem mass spectrometry (LC/MS/MS) methods generally miss low-occupancy modifications in complex analyses. Here, we present a data-independent acquisition (DIA) LC/MS-based approach, leveraging the high IR absorbance of sulfoxides at 10.6 μm, for selective dissociation and discovery of S-sulfonated peptides. Across peptide standards and protein digests, we demonstrate selective infrared multiphoton dissociation (IRMPD) of S-sulfonated peptides in the background of unmodified peptides. This selective DIA IRMPD LC/MS-based approach allows identification and annotation of S-sulfonated peptides across complex mixtures while providing sufficient sequence information to localize the modification site.

Between two stools: occupational injuries and risk factors for temporary agency workers

Purpose

Research shows that the risk of work-related disorders is higher among temporary agency workers than among other employees. The purpose of this paper is to describe the working conditions of temporary agency workers and explains which factors contribute towards work-related disorders for this group.

Design/methodology/approach

This paper is based on a survey responded to by 482 agency workers in Sweden. The dependent variable is the prevalence of work-related disorders. Independent variables include personal characteristics, job characteristics, employment characteristics and temporary agency work characteristics.

Findings

The study indicates several risk factors: holding a position as a blue-collar worker; being assigned to more physically demanding work tasks and having fewer opportunities to learn new things than client organization employees; lacking training for work tasks; and lacking clarity regarding which work tasks to do during an assignment.

Originality/value

The theoretical implications of this study are related to the dual employment-management relationship in temporary agency work where the temporary work agency and client organization follow different logics. The logic in the employment relationship is to contract temporary agency workers out to client organizations, thus there is no time for formal training. The logic in the management relationship lies in making temporary agency workers profitable as soon as possible, encouraging shortcuts in training and instruction; thus, temporary agency workers risk being left with a lack of clarity regarding what to do and how to do it.

MR and ultrasound in screening of patients with suspected biliary tract disease

Purpose: The diagnostic value and cost-efficiency of MR imaging were compared with US before endoscopic retrograde cholangiopancreatography (ERCP) in patients with clinically suspected biliary tract disease.

Material and Methods: In a prospective study of 219 patients, 85 were examined with both MR and US before ERCP.

Results: To find the correct diagnosis in the jaundiced patients the sensitivity of US, MR and ERCP was 53%, 93%, and 89%, respectively. In the patients with abdominal upper quadrant pain and normal serum bilirubin, the sensitivity of US, MR and ERCP was 50%, 100% and 70%, respectively. Examination with MR costs four times more than US. Screening with US and supplemental MR in non-diagnostic cases would cost 80% of the total amount compared to screening with MR only.

Conclusion: MR had a higher sensitivity than US for diagnosing biliary tract disease and MR was superior to US in visualising stones in the common bile duct and in diagnosing the cause of cholestasis. However, screening with US and supplemental MR in non-diagnostic cases is at present most cost-effective. With increased accessibility and slightly lower costs, MR will probably replace US as screening method in patients with suspected biliary tract disease.

MR characteristics of acute cholangitis

Purpose: To describe the MR appearance of acute cholangitis and discuss the role of MR imaging as a diagnostic method in this disease.

Material and Methods: Of 60 patients with clinical acute cholangitis, 12 were examined with MR before endoscopic retrograde pancreatography (ERCP). A retrospective review was performed of MR and ERCP findings. The MR findings registered were presence of biliary duct dilatation, intraluminal filling defects due to stones or sludge, bands of mucosal oedema of the biliary ducts, intra- and retroperitoneal oedema/fluid, and definition of the cause of obstruction, e.g. stones, stenosis or tumour was made.

Results: Acute cholangitis was related to obstruction from choledocholithiasis (n=8), pancreatic cancer (n=1), benign biliary duct stricture (n=1), papillary stenosis (n=1) and without evidence of an obstructing cause (n=1). One patient had an acute obstructive suppurative (toxic) cholangitis.

Conclusion: MR imaging has a role in the non-invasive radiographic arsenal of techniques to confirm or exclude the diagnosis of acute cholangitis, especially in older patients where the clinical symptoms may be vague.

MR imaging of upper abdomen following cholecystectomy: Normal and abnormal findings

Purpose: To describe the normal MR appearance after cholecystectomy and the findings in patients with postoperative complications using fast pulse sequences in abdominal MR imaging.

Material and Methods: In a prospective study of 119 patients, 64 were examined with MR after cholecystectomy. In total, 56 patients with uncomplicated cholecystectomy were examined with MR 1–5 days (mean 1.6 days) after cholecystectomy. Nine patients had an abdominal postoperative complication and 8 of these were examined with MR after the complication commenced 1–12 days after the cholecystectomy.

Results: Oedema in the gallbladder fossa was the only finding in 39 patients (61%), all with uneventful recovery. Small fluid collections in an area consistent with the gallbladder fossa were seen in 9/64 (14%) patients, of which 3 had surgical complications: 1 bleeding and 2 bile duct leakage. Twenty-two (34%) patients had small locally situated fluid collections adjacent to the liver, 14 were uneventful and 8 showed postoperative surgical complications. Seven patients had fluid in the rest of the abdomen of which 5 had surgical complications; 4 due to bile duct leakage and 1 acute pancreatitis. One patient had a postoperative bleeding not seen on MR images.

Conclusion: MR is very sensitive in detecting fluid collections. Early MR findings following cholecystectomy are normally only subtle changes, mainly in the gallbladder fossa. Fluid collections diagnosed elsewhere than in the gallbladder fossa usually indicate a surgical complication and a surgical complication is unlikely if MR fails to show a fluid collection.

MR imaging in clinically suspected acute cholecystitis: A comparison with ultrasonography

Purpose: The diagnostic value of fast pulse sequences in MR imaging was compared with US in patients with clinically suspected acute cholecystitis.

Material and Methods: In a prospective study of 94 patients, 35 were examined with both MR and US within 24 h.

Results: MR diagnoses were acute cholecystitis in 23, gallbladder and common bile duct stones in 3, other pathologic conditions of the abdomen in 7 and normal in 2 patients. US diagnoses were acute cholecystitis in 17, gallbladder stones in 8, other pathologic conditions of the abdomen in 2, normal in 5 and non-conclusive in 3 patients.

Conclusion: MR has a higher sensitivity than US for diagnosing acute cholecystitis and, with increased accessibility, may be the first imaging method.

A major population of mucosal memory CD4+ T cells, coexpressing IL-18Rα and DR3, display innate lymphocyte functionality

Mucosal tissues contain large numbers of memory CD4(+) T cells that, through T-cell receptor-dependent interactions with antigen-presenting cells, are believed to have a key role in barrier defense and maintenance of tissue integrity. Here we identify a major subset of memory CD4(+) T cells at barrier surfaces that coexpress interleukin-18 receptor alpha (IL-18Rα) and death receptor-3 (DR3), and display innate lymphocyte functionality. The cytokines IL-15 or the DR3 ligand tumor necrosis factor (TNF)-like cytokine 1A (TL1a) induced memory IL-18Rα(+)DR3(+)CD4(+) T cells to produce interferon-γ, TNF-α, IL-6, IL-5, IL-13, granulocyte-macrophage colony-stimulating factor (GM-CSF), and IL-22 in the presence of IL-12/IL-18. TL1a synergized with IL-15 to enhance this response, while suppressing IL-15-induced IL-10 production. TL1a- and IL-15-mediated cytokine induction required the presence of IL-18, whereas induction of IL-5, IL-13, GM-CSF, and IL-22 was IL-12 independent. IL-18Rα(+)DR3(+)CD4(+) T cells with similar functionality were present in human skin, nasal polyps, and, in particular, the intestine, where in chronic inflammation they localized with IL-18-producing cells in lymphoid aggregates. Collectively, these results suggest that human memory IL-18Rα(+)DR3(+) CD4(+) T cells may contribute to antigen-independent innate responses at barrier surfaces.

Electron capture dissociation of divalent metal-adducted sulfated N-glycans released from bovine thyroid stimulating hormone

Sulfated N-glycans released from bovine thyroid stimulating hormone (bTSH) were ionized with the divalent metal cations Ca(2+), Mg(2+), and Co by electrospray ionization (ESI). These metal-adducted species were subjected to infrared multiphoton dissociation (IRMPD) and electron capture dissociation (ECD) and the corresponding fragmentation patterns were compared. IRMPD generated extensive glycosidic and cross-ring cleavages, but most product ions suffered from sulfonate loss. Internal fragments were also observed, which complicated the spectra. ECD provided complementary structural information compared with IRMPD, and all observed product ions retained the sulfonate group, allowing sulfonate localization. To our knowledge, this work represents the first application of ECD towards metal-adducted sulfated N-glycans released from a glycoprotein. Due to the ability of IRMPD and ECD to provide complementary structural information, the combination of the two strategies is a promising and valuable tool for glycan structural characterization. The influence of different metal ions was also examined. Calcium adducts appeared to be the most promising species because of high sensitivity and ability to provide extensive structural information.

Electron detachment dissociation of underivatized chloride-adducted oligosaccharides

Chloride anion attachment has previously been shown to aid determination of saccharide anomeric configuration and generation of linkage information in negative ion post-source decay MALDI tandem mass spectrometry. Here, we employ electron detachment dissociation (EDD) and collision activated dissociation (CAD) for the structural characterization of underivatized oligosaccharides bearing a chloride ion adduct. Both neutral and sialylated oligosaccharides are examined, including maltoheptaose, an asialo biantennary glycan (NA2), disialylacto-N-tetraose (DSLNT), and two LS tetrasaccharides (LSTa and LSTb). Gas-phase chloride-adducted species are generated by negative ion mode electrospray ionization. EDD and CAD spectra of chloride-adducted oligosaccharides are compared to the corresponding spectra for doubly deprotonated species not containing a chloride anion to assess the role of chloride adduction in the stimulation of alternative fragmentation pathways and altered charge locations allowing detection of additional product ions. In all cases, EDD of singly chloridated and singly deprotonated species resulted in an increase in observed cross-ring cleavages, which are essential to providing saccharide linkage information. Glycosidic cleavages also increased in EDD of chloride-adducted oligosaccharides to reveal complementary structural information compared to traditional (non-chloride-assisted) EDD and CAD. Results indicate that chloride adduction is of interest in alternative anion activation methods such as EDD for oligosaccharide structural characterization.

Characterization of O-sulfopeptides by negative ion mode tandem mass spectrometry: superior performance of negative ion electron capture dissociation

Positive ion mode collision-activated dissociation tandem mass spectrometry (CAD MS/MS) of O-sulfopeptides precludes determination of sulfonated sites due to facile proton-driven loss of the highly labile sulfonate groups. A previously proposed method for localizing peptide and protein O-sulfonation involves derivatization of nonsulfonated tyrosines followed by positive ion CAD MS/MS of the corresponding modified sulfopeptides for diagnostic sulfonate loss. This indirect method relies upon specific and complete derivatization of nonsulfonated tyrosines. Alternative MS/MS activation methods, including positive ion metastable atom-activated dissociation (MAD) and metal-assisted electron transfer dissociation (ETD) or electron capture dissociation (ECD) provide varying degrees of sulfonate retention. Sulfonate retention has also been reported following negative ion MAD and electron detachment dissociation (EDD), which also operates in negative ion mode in which sulfonate groups are less labile than in positive ion mode. However, an MS/MS activation technique that can effectively preserve sulfonate groups while providing extensive backbone fragmentation (translating to sequence information, including sulfonated sites) with little to no noninformative small molecule neutral loss has not previously been realized. Here, we report that negative ion CAD, EDD, and negative ETD (NETD) result in sulfonate retention mainly at higher charge states with varying degrees of fragmentation efficiency and sequence coverage. Similar to previous observations from CAD of sulfonated glycosaminoglycan anions, higher charge states translate to a higher probability of deprotonation at the sulfonate groups thus yielding charge-localized fragmentation without loss of the sulfonate groups. However, consequently, higher sulfonate retention comes at the price of lower sequence coverage in negative ion CAD. Fragmentation efficiency/sequence coverage averaged 19/6% and 33/20% in EDD and NETD, respectively, both of which are only applicable to multiply-charged anions. In contrast, the recently introduced negative ion ECD showed an average fragmentation efficiency of 69% and an average sequence coverage of 82% with complete sulfonate retention from singly- and doubly-deprotonated sulfopeptide anions.

Work Organizational Outcomes of the Use of Temporary Agency Workers

This article examines work organizational dynamics in workplaces using temporary agency workers. Previous research has principally either emphasized one effect, the division into core and periphery, or criticized this effect. This article contributes to a more nuanced analysis of how the work organization of user firms is affected by the use of temporary agency workers. Crucial factors influencing the outcome include: how agency workers are integrated into the work organization; the skills required for the work performed by agency workers; the duration of assignments; the induction time; and the access to competence development. Based on ten Swedish cases, our analysis shows that the use of temporary agency workers has three different outcomes: (1) The Core and Periphery outcome is in line with previous research on ‘the flexible firm’ whereby temporary agency workers are assigned simple work tasks and user firm employees perform advanced work tasks; (2) the All Core outcome entails using agency workers for the same advanced work tasks as user firm employees. Contradicting the theory of ‘the flexible firm’, our study shows that temporary agency workers contribute to functional flexibility; (3) the third outcome, All Periphery, occurs when the work organization is adapted to the use of low-skilled agency workers who are easily introduced into the workplace and easily terminated. However, adapting the work organization to the use of temporary agency workers also influences user firm employees, leading to deskilling and a deteriorated work organization for all workers at that workplace.

Acyl-CoA subunit selectivity in the pikromycin polyketide synthase PikAIV: steady-state kinetics and active-site occupancy analysis by FTICR-MS

Polyketide natural products generated by type I modular polyketide synthases (PKSs) are vital components in our drug repertoire. To reprogram these biosynthetic assembly lines, we must first understand the steps that occur within the modular "black boxes." Herein, key steps of acyl-CoA extender unit selection are explored by in vitro biochemical analysis of the PikAIV PKS model system. Two complementary approaches are employed: a fluorescent-probe assay for steady-state kinetic analysis, and Fourier Transform Ion Cyclotron Resonance-mass spectrometry (FTICR-MS) to monitor active-site occupancy. Findings from five enzyme variants and four model substrates have enabled a model to be proposed involving catalysis based upon acyl-CoA substrate loading followed by differential rates of hydrolysis. These efforts suggest a strategy for future pathway engineering efforts using unnatural extender units with slow rates of hydrolytic off-loading from the acyltransferase domain.

Electron detachment dissociation and negative ion infrared multiphoton dissociation of electrosprayed intact proteins

In top-down proteomics, intact gaseous proteins are fragmented in a mass spectrometer by, e.g., electron capture dissociation (ECD) to obtain structural information. By far, most top-down approaches involve dissociation of protein cations. However, in electrospray ionization of phosphoproteins, the high acidity of phosphate may contribute to the formation of intramolecular hydrogen bonds or salt bridges, which influence subsequent fragmentation behavior. Other acidic proteins or proteins with regions containing multiple acidic residues may also be affected similarly. Negative ion mode, on the other hand, may enhance deprotonation and unfolding of multiply phosphorylated or highly acidic protein regions. Here, activated ion electron detachment dissociation (AI-EDD) and negative ion infrared multiphoton dissociation (IRMPD) were employed to investigate the fragmentation of intact proteins, including multiply phosphorylated β-casein, calmodulin, and glycosylated ribonuclease B. Compared to AI-ECD and positive ion IRMPD, AI-EDD and negative ion IRMPD provide complementary protein sequence information, particularly in regions with high acidity, including the multiply phosphorylated region of β-casein.

Electron induced dissociation of singly deprotonated peptides

Dissociation of singly charged species is more challenging compared with that of multiply charged precursor ions because singly charged ions are generally more stable. In collision activated dissociation (CAD), singly charged ions also gain less kinetic energy in a fixed electric field compared with multiply charged species. Furthermore, ion-electron and ion-ion reactions that frequently provide complementary and more extensive fragmentation compared with CAD typically require multiply charged precursor ions. Here, we investigate electron induced dissociation (EID) of singly deprotonated peptides and compare the EID fragmentation patterns with those observed in negative ion mode CAD. Fragmentation induced upon electron irradiation and collisional activation is not specific and results in the formation of a wide range of product ions, including b-, y-, a-, x-, c-, and z-type ions. Characteristic amino acid side chain losses are detected in both techniques. However, differences are also observed between EID and CAD spectra of the same species, including formation of odd-electron species not seen in CAD, in EID. Furthermore, EID frequently results in more extensive fragmentation compared with CAD. For modified peptides, EID resulted in retention of sulfonation and phosphorylation, allowing localization of the modification site. The observed differences are likely due to both vibrational and electronic excitation in EID, whereas only the former process occurs in CAD.

Structural Characterization of Carbohydrates by Fourier Transform Tandem Mass Spectrometry

Fourier transform tandem mass spectrometry (MS/MS) provides high mass accuracy, high sensitivity, and analytical versatility and has therefore emerged as an indispensable tool for structural elucidation of biomolecules. Glycosylation is one of the most common posttranslational modifications, occurring in ~50% of proteins. However, due to the structural diversity of carbohydrates, arising from non-template driven biosynthesis, achievement of detailed structural insight is highly challenging. This review briefly discusses carbohydrate sample preparation and ionization methods, and highlights recent developments in alternative high-resolution MS/MS strategies, including infrared multiphoton dissociation (IRMPD), electron capture dissociation (ECD), and electron detachment dissociation (EDD), for carbohydrates with a focus on glycans and proteoglycans from mammalian glycoproteins.

Electron detachment dissociation of fluorescently labeled sialylated oligosaccharides

We explored the application of electron detachment dissociation (EDD) and infrared multiphoton dissociation (IRMPD) tandem mass spectrometry to fluorescently labeled sialylated oligosaccharides. Standard sialylated oligosaccharides and a sialylated N-linked glycan released from human transferrin were investigated. EDD yielded extensive glycosidic cleavages and cross-ring cleavages in all cases studied, consistently providing complementary structural information compared with infrared multiphoton dissociation. Neutral losses and satellite ions such as C-2H ions were also observed following EDD. In addition, we examined the influence of different fluorescent labels. The acidic label 2-aminobenzoic acid (2-AA) enhanced signal abundance in negative-ion mode. However, few cross-ring fragments were observed for 2-AA-labeled oligosaccharides. The neutral label 2-aminobenzamide (2-AB) resulted in more cross-ring cleavages compared with 2-AA-labeled species, but not as extensive fragmentation as for native oligosaccharides, likely resulting from altered negative charge locations from introduction of the fluorescent tag.

Meta-omic characterization of the marine invertebrate microbial consortium that produces the chemotherapeutic natural product ET-743

In many macroorganisms, the ultimate source of potent biologically active natural products has remained elusive due to an inability to identify and culture the producing symbiotic microorganisms. As a model system for developing a meta-omic approach to identify and characterize natural product pathways from invertebrate-derived microbial consortia, we chose to investigate the ET-743 (Yondelis) biosynthetic pathway. This molecule is an approved anticancer agent obtained in low abundance (10(-4)-10(-5) % w/w) from the tunicate Ecteinascidia turbinata and is generated in suitable quantities for clinical use by a lengthy semisynthetic process. On the basis of structural similarities to three bacterial secondary metabolites, we hypothesized that ET-743 is the product of a marine bacterial symbiont. Using metagenomic sequencing of total DNA from the tunicate/microbial consortium, we targeted and assembled a 35 kb contig containing 25 genes that comprise the core of the NRPS biosynthetic pathway for this valuable anticancer agent. Rigorous sequence analysis based on codon usage of two large unlinked contigs suggests that Candidatus Endoecteinascidia frumentensis produces the ET-743 metabolite. Subsequent metaproteomic analysis confirmed expression of three key biosynthetic proteins. Moreover, the predicted activity of an enzyme for assembly of the tetrahydroisoquinoline core of ET-743 was verified in vitro. This work provides a foundation for direct production of the drug and new analogues through metabolic engineering. We expect that the interdisciplinary approach described is applicable to diverse host-symbiont systems that generate valuable natural products for drug discovery and development.

Chemoenzymatic synthesis of cryptophycin anticancer agents by an ester bond-forming non-ribosomal peptide synthetase module

Cryptophycins (Crp) are a group of cyanobacterial depsipeptides with activity against drug-resistant tumors. Although they have been shown to be promising, further efforts are required to return these highly potent compounds to the clinic through a new generation of analogues with improved medicinal properties. Herein, we report a chemosynthetic route relying on the multifunctional enzyme CrpD-M2 that incorporates a 2-hydroxy acid moiety (unit D) into Crp analogues. CrpD-M2 is a unique non-ribosomal peptide synthetase (NRPS) module comprised of condensation-adenylation-ketoreduction-thiolation (C-A-KR-T) domains. We interrogated A-domain 2-keto and 2-hydroxy acid activation and loading, and KR domain activity in the presence of NADPH and NADH. The resulting 2-hydroxy acid was elongated with three synthetic Crp chain elongation intermediate analogues through ester bond formation catalyzed by CrpD-M2 C domain. Finally, the enzyme-bound seco-Crp products were macrolactonized by the Crp thioesterase. Analysis of these sequential steps was enabled through LC-FTICR-MS of enzyme-bound intermediates and products. This novel chemoenzymatic synthesis of Crp involves four sequential catalytic steps leading to the incorporation of a 2-hydroxy acid moiety in the final chain elongation intermediate. The presented work constitutes the first example where a NRPS-embedded KR domain is employed for assembly of a fully elaborated natural product, and serves as a proof-of-principle for chemoenzymatic synthesis of new Crp analogues.

Polyketide β-branching in bryostatin biosynthesis: identification of surrogate acetyl-ACP donors for BryR, an HMG-ACP synthase

In vitro analysis of natural product biosynthetic gene products isolated from unculturable symbiotic bacteria is necessary to probe the functionalities of these enzymes. Herein, we report the biochemical characterization of BryR, the 3-hydroxy-3-methylglutaryl (HMG)-CoA synthase (HMGS) homolog implicated in β-branching at C13 and C21 of the core ring system from the bryostatin metabolic pathway (Bry). We confirmed the activity of BryR using two complementary methods, radio-SDS PAGE, and Fourier transform ion cyclotron resonance-mass spectrometry (FTICR-MS). The activity of BryR depended on pairing of the native acetoacetyl-BryM3 acceptor acyl carrier protein (ACP) with an appropriate donor acetyl-ACP from a heterologous HMGS cassette. Additionally, the ability of BryR to discriminate between various ACPs was assessed using a surface plasmon resonance (SPR)-based protein-protein binding assay. Our data suggest that specificity for a protein-bound acyl group is a distinguishing feature between HMGS homologs found in PKS or PKS/NRPS biosynthetic pathways and those of primary metabolism. These findings reveal an important example of molecular recognition between protein components that are essential for biosynthetic fidelity in natural product assembly and modification.

Hydrogen tunneling in adenosylcobalamin-dependent glutamate mutase: evidence from intrinsic kinetic isotope effects measured by intramolecular competition

Hydrogen atom transfer reactions between the substrate and coenzyme are key mechanistic features of all adenosylcobalamin-dependent enzymes. For one of these enzymes, glutamate mutase, we have investigated whether hydrogen tunneling makes a significant contribution to the mechanism by examining the temperature dependence of the deuterium kinetic isotope effect associated with the transfer of a hydrogen atom from methylaspartate to the coenzyme. To do this, we designed a novel intramolecular competition experiment that allowed us to measure the intrinsic kinetic isotope effect, even though hydrogen transfer may not be rate-determining. From the Arrhenius plot of the kinetic isotope effect, the ratio of the pre-exponential factors (A(H)/A(D)) was 0.17 +/- 0.04 and the isotope effect on the activation energy [DeltaE(a(D-H))] was 1.94 +/- 0.13 kcal/mol. The results imply that a significant degree of hydrogen tunneling occurs in glutamate mutase, even though the intrinsic kinetic isotope effects are well within the semiclassical limit and are much smaller than those measured for other AdoCbl enzymes and model reactions for which hydrogen tunneling has been implicated.