Aspirin-exacerbated respiratory disease is associated with variants in filaggrin, epithelial integrity, and cellular interactions

Background

Previous studies have determined that up to 6% of patients with aspirin-exacerbated respiratory disease (AERD) have family history of AERD, indicating a possible link with genetic polymorphisms. However, whole exome sequencing (WES) studies of such associations are currently lacking.

Objectives

We sought to examine whether WES can identify pathogenic variants associated with AERD.

Methods

Diagnoses of AERD were confirmed in patients with nasal polyps and asthma. WES was performed using an Illumina sequencing platform. Human Phenotype Ontology terms were used to define the patients' phenotypes. Exomiser was used to annotate, filter, and prioritize possible disease-causing genetic variants.

Results

Of 39 patients with AERD, 41% reported a family history of asthma and 5% reported a family history of AERD. Pathogenic exome variants in the filaggrin gene (FLG) were found in 2 patients (5%). Other variants not known to be pathogenic were detected in an additional 16 patients (41%) in genes related to epithelial integrity and cellular interactions, including genes encoding desmoglein 3 (DSG3), dynein axonemal heavy chain 9 (DNAH9), collagen type VII alpha 1 chain (COL7A1), collagen type XVII alpha 1 chain (COL17A1), chromodomain helicase DNA binding protein-7 (CHD7), TSC complex subunit 2/tuberous sclerosis-2 protein (TSC2), P-selectin (SELP), and platelet-derived growth factor receptor-alpha (PDGFRA).

Conclusion

WES identified a monogenic susceptibility to AERD in 5% of patients with FLG pathogenic variants. Other variants not previously identified as pathogenic were found in genes relevant to epithelial integrity and cellular interactions and may further reveal genetic factors that contribute to this condition.

Sex, Ethnicity, Body Mass Index, and Environmental Exposures Associated With NSAID-Exacerbated Respiratory Disease Symptom Sequence

BACKGROUND

Nonsteroidal anti-inflammatory drug (NSAID)-exacerbated respiratory disease (N-ERD) has a triad of symptoms: nasal polyposis, asthma, and NSAID hypersensitivity. Little is known about symptom timing and disease progression.

OBJECTIVE

The aim of this study is to characterize disease progression in N-ERD.

METHODS

Patients with N-ERD were prospectively interviewed and classified into 4 groups based on their first symptom at initial N-ERD onset (asthma, nasal polyps, NSAID hypersensitivity, or all concurrently). Associations of patient characteristics with the 4 groups were examined, along with associations within the "asthma first" group.

RESULTS

Patients (N = 240) were mostly female (68%) and self-identified as non-White (77%). Half (N = 119) reported asthma as the earliest symptom in the N-ERD triad. Compared with other groups, "asthma first" was associated with younger age of onset (25 years, standard error ±1.3, P < .001) and higher body mass index (BMI) (odds ratio [OR] = 1.3, 95% confidence interval [CI]: 1.06-1.7, P = .02). In this group, age of onset <20 years was associated with female sex, Latino ethnicity, and higher BMI (all P < .05). The "NSAID sensitivity first" group was significantly associated with male sex (OR = 3.3, 95% CI: 1.5-7.4, P = .004) and pollution exposure (OR = 4.4, 95% CI: 1.6-11.9, P = .003). At the initial presentation, 27% of patients were unaware of their N-ERD diagnosis. Black and Latino patients were more likely to be unaware of their N-ERD diagnosis compared with White (P = .003). The median diagnostic delay was 3 years (interquartile range: 0-5 years).

CONCLUSIONS

In this cohort, N-ERD is highly variable in onset and progression, with sex, BMI, race and ethnicity, and environmental exposures significantly associated with disease patterns and diagnostic delay.

Acute and Longer-Term Effects of COVID-19 on Auditory and Vestibular Symptoms

OBJECTIVE

To evaluate long-term effects of COVID-19 on auditory and vestibular symptoms in a diverse cohort impacted by the initial 2020 COVID-19 infection in the pandemic's epicenter, before vaccine availability.

STUDY DESIGN

Cohort study of individuals with confirmed COVID-19 infection, diagnosed in the March-May 2020 infection wave. A randomized, retrospective chart review of 1,352 individuals was performed to identify those with documented new or worsening auditory (aural fullness, tinnitus, hyperacusis, hearing loss) or vestibular (dizziness, vertigo) symptoms. Those with documented symptoms (613 of the 1,352 initial cohort) were contacted for a follow-up telephone survey in 2021-2022 to obtain self-report of aforementioned symptoms.

SETTING

Academic tertiary hospital system in Bronx, NY.

PATIENTS

Adults 18 to 99 years old with confirmed COVID-19 infection, alive at time of review. One hundred forty-eight charts were excluded for restricted access, incomplete data, no COVID-19 swab, or deceased at time of review.

INTERVENTION

Confirmed COVID-19 infection, March to May 2020.

MAIN OUTCOMES MEASURES

Auditory and vestibular symptoms documented in 2020 medical records and by self-report on 2021 to 2022 survey.

RESULTS

Among the 74 individuals with documented symptoms during the first 2020 COVID-19 wave who participated in the 2021 to 2022 follow-up survey, 58% had documented vestibular symptoms initially in 2020, whereas 43% reported vestibular symptoms on the 2021 to 2022 survey ( p = 0.10). In contrast, 9% had documented auditory symptoms initially in 2020 and 55% reported auditory symptoms on the 2021 to 2022 survey ( p < 0.01).

CONCLUSIONS

COVID-19 may impact vestibular symptoms early and persistently, whereas auditory effects may have more pronounced long-term impact, suggesting the importance of continually assessing COVID-19 patients.

Elaborate biologic approval process delays care of patients with moderate-to-severe asthma

Background

mAbs (biologics) are indicated in patients with poorly controlled moderate-to-severe asthma. The process of prior authorization and administration of a biologic requires exceptional commitment from clinical teams.

Objective

Our aim was to evaluate the process of approval and administration of biologics for asthma and determine the most common reasons associated with denials of biologics and delays in administration.

Methods

We examined the records of patients with asthma who were prescribed biologics from January 2018 to January 2020 at 2 centers, Montefiore Medical Center (Bronx, NY) and Scripps Clinics (San Diego, Calif). Demographics, insurance information, and details on the approval process were collected.

Results

After querying of electronic health records, the records of 352 and 70 patients with moderate-to-severe asthma were included from Montefiore and Scripps, respectively. Most patients at Montefiore (58.2%) were insured under Managed Care Medicaid (MC Medicaid), whereas most patients at Scripps (61.4%) had commercial insurance. The median times from prescription to administration of a biologic were similar: 34 days (interquartile range [IQR] = 18-63 days) and 34 days (IQR = 22.5-56.0 days) (P = .97) for Montefiore and Scripps, respectively. However, the median approval time for Montefiore was 6 days (IQR = 1-20 days) and that for Scripps was 22 days (IQR = 10-36 days) (P < .001). Approval times for prescriptions requiring appeals were significantly longer than for prescriptions approved after the initial submission: 23 days versus 2.5 days and 40.5 days versus 15.5 days (for Montefiore and Scripps, respectively [P < .001 for both]).

Conclusions

Lengthy appeals contribute to delays between prescribing and administering a biologic. Site-specific practices and insurance coverage influence approval timing of the biologics for asthma.

The role of oxylipins in NSAID-exacerbated respiratory disease (N-ERD)

Nonsteroidal anti-inflammatory drug (NSAID)-exacerbated respiratory disease (N-ERD) is characterized by nasal polyp formation, adult-onset asthma, and hypersensitivity to all cyclooxygenase-1 (COX-1) inhibitors. Oxygenated lipids are collectively known as oxylipins and are polyunsaturated fatty acids (PUFA) oxidation products. The most extensively researched oxylipins being the eicosanoids formed from arachidonic acid (AA). There are four major classes of eicosanoids including leukotrienes, prostaglandins, thromboxanes, and lipoxins. In N-ERD, the underlying inflammatory process of the upper and lower respiratory systems begins and occurs independently of NSAID consumption and is due to the overproduction of cysteinyl leukotrienes. Leukotriene mediators all induce edema, bronchoconstriction, and airway mucous secretion. Thromboxane A2 is a potent bronchoconstrictor and induces endothelial adhesion molecule expression. Elevated Prostaglandin D2 metabolites lead to vasoconstriction, additionally impaired up-regulation of prostaglandin E2 leads to symptoms seen in N-ERD as it is essential for maintaining homeostasis of inflammatory responses in the airway and has bronchoprotective and anti-inflammatory effects. A characteristic feature of N-ERD is diminished lipoxin levels, this decreased capacity to form endogenous mediators with anti-inflammatory properties could facilitate local inflammatory response and expose bronchial smooth muscle to relatively unopposed actions of broncho-constricting substances. Treatment options, such as leukotriene modifying agents, aspirin desensitization, biologic agents and ESS, appear to influence eicosanoid pathways, however more studies need to be done to further understand the role of oxylipins. Besides AA-derived eicosanoids, other oxylipins may also pay a role but have not been sufficiently studied. Identifying pathogenic N-ERD mechanism is likely to define more effective treatment targets.

New concepts for the pathogenesis and management of aspirin-exacerbated respiratory disease

PURPOSE OF REVIEW

The purpose of this review is to provide a comprehensive summary of the current understanding of the pathogenesis of aspirin-exacerbated respiratory disease (AERD), and an update on its management.

RECENT FINDINGS

Elevated levels of 15-oxo-eicosatetraenoic acid (15-Oxo-ETE), a newly described metabolite of arachidonic acid, have been identified in nasal polyps of AERD patients. In nasal polyps, activated basophils, and interleukin-5 -receptor-α-positive IL-5Rα+ plasma cells are associated with more severe nasal polyposis in AERD. Alveolar monocyte-derived macrophages and their persistent proinflammatory activation were suggested as putative factors contributing to AERD. Although not AERD-specific, three biological agents are now available for the management of both nasal polyposis and asthma.

SUMMARY

A newly downstream product of 15-lipoxygenase, 15-Oxo-ETE, was recently found to be significantly elevated in nasal polyps from AERD patients. This eicosanoid metabolite likely originates from an interplay between epithelial cells and mast cells. Nasal polyp basophils, IL-5Rα+ plasma cells, and alveolar macrophages were identified as important contributors to inflammation in AERD. Besides traditional aspirin desensitization and treatment for AERD management, several biologics for treatment of asthma are available, including three that have been approved for nasal polyposis. These biologic agents show variable rates of success in controlling AERD symptoms.

Severe COVID-19 Is Associated With an Altered Upper Respiratory Tract Microbiome

Background

The upper respiratory tract (URT) is the portal of entry of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and SARS-CoV-2 likely interacts with the URT microbiome. However, understanding of the associations between the URT microbiome and the severity of coronavirus disease 2019 (COVID-19) is still limited.

Objective

Our primary objective was to identify URT microbiome signature/s that consistently changed over a spectrum of COVID-19 severity.

Methods

Using data from 103 adult participants from two cities in the United States, we compared the bacterial load and the URT microbiome between five groups: 20 asymptomatic SARS-CoV-2-negative participants, 27 participants with mild COVID-19, 28 participants with moderate COVID-19, 15 hospitalized patients with severe COVID-19, and 13 hospitalized patients in the ICU with very severe COVID-19.

Results

URT bacterial load, bacterial richness, and within-group microbiome composition dissimilarity consistently increased as COVID-19 severity increased, while the relative abundance of an amplicon sequence variant (ASV), Corynebacterium_unclassified.ASV0002, consistently decreased as COVID-19 severity increased.

Conclusions

We observed that the URT microbiome composition significantly changed as COVID-19 severity increased. The URT microbiome could potentially predict which patients may be more likely to progress to severe disease or be modified to decrease severity. However, further research in additional longitudinal cohorts is needed to better understand how the microbiome affects COVID-19 severity.

Aspirin Actions in Treatment of NSAID-Exacerbated Respiratory Disease

Non-steroidal Anti-inflammatory drugs (NSAID)-exacerbated respiratory disease (N-ERD) is characterized by nasal polyposis, chronic rhinosinusitis, adult-onset asthma and hypersensitive reactions to cyclooxygenase-1 (COX-1) inhibitors. Among the available treatments for this disease, a combination of endoscopic sinus surgery followed by aspirin desensitization and aspirin maintenance therapy has been an effective approach. Studies have shown that long-term aspirin maintenance therapy can reduce the rate of nasal polyp recurrence in patients with N-ERD. However, the exact mechanism by which aspirin can both trigger and suppress airway disease in N-ERD remains poorly understood. In this review, we summarize current knowledge of aspirin effects in N-ERD, cardiovascular disease, and cancer, and consider potential mechanistic pathways accounting for the effects of aspirin in N-ERD.

COVID-19-Induced Anosmia and Ageusia Are Associated With Younger Age and Lower Blood Eosinophil Counts

BACKGROUND

Anosmia and ageusia are symptoms commonly associated with COVID-19, but the relationship with disease severity, onset and recovery are unclear.

OBJECTIVE

To examine factors associated with anosmia and ageusia and the recovery from these symptoms in an ethnically diverse cohort.

METHODS

Individuals tested for SARS-CoV-2 between March and April 2020 were eligible for the study. Randomly selected participants answered a telephone questionnaire on COVID-19 symptoms with a focus on anosmia and ageusia. Additionally, relevant past medical history and data on the COVID-19 clinical course were obtained from electronic medical records. 486 patients were in the COVID-19 group and 103 were COVID-19-negative.

RESULTS

Patients who were younger were more likely to report anosmia and/or ageusia (odds ratio (OR) for anosmia per 1-year increase in age: 0·98, 95%CI:0-97-0·99, p = 0·003; for ageusia: 0·98, 95%CI:0·97-0·99, p = 0·005) as were patients with lower eosinophil counts (OR for anosmia per 0.1-K/μL increase in eosinophils: 0·02, 95%CI:0·001-0·46, p = 0·01, for ageusia 0·10, 95%CI:0·01-0·97, p = 0·047). Male gender was independently associated with a lower probability of ageusia (OR:0·56, 95%CI:0·38-0·82, p = 0·003) and earlier sense of taste recovery (HR:1·44, 95%CI:1·05-1·98, p = 0·02). Latinos showed earlier sense of taste recovery than white patients (HR:1·82, 95%CI:1·05-3·18, p = 0·03).

CONCLUSION

Anosmia and ageusia were more common among younger patients and those with lower blood eosinophil counts. Ageusia was less commonly reported among men, and time to taste recovery was earlier among both men and Latinos.

Structure and Enzymatic Properties of an Unusual Cysteine Tryptophylquinone-Dependent Glycine Oxidase from Pseudoalteromonas luteoviolacea

Glycine oxidase from Pseudoalteromonas luteoviolacea (PlGoxA) is a cysteine tryptophylquinone (CTQ)-dependent enzyme. Sequence analysis and phylogenetic analysis place it in a newly designated subgroup (group IID) of a recently identified family of LodA-like proteins, which are predicted to possess CTQ. The crystal structure of PlGoxA reveals that it is a homotetramer. It possesses an N-terminal domain with no close structural homologues in the Protein Data Bank. The active site is quite small because of intersubunit interactions, which may account for the observed cooperativy toward glycine. Steady-state kinetic analysis yielded the following values: k_cat = 6.0 ± 0.2 s^-1, K_0.5 = 187 ± 18 μM, and h = 1.77 ± 0.27. In contrast to other quinoprotein amine dehydrogenases and oxidases that exhibit anomalously large primary kinetic isotope effects on the rate of reduction of the quinone cofactor by the amine substrate, no significant primary kinetic isotope effect was observed for this reaction of PlGoxA. The absorbance spectrum of glycine-reduced PlGoxA exhibits features in the range of 400-650 nm that have not previously been seen in other quinoproteins. Thus, in addition to the unusual structural features of PlGoxA, the kinetic and chemical reaction mechanisms of the reductive half-reaction of PlGoxA appear to be distinct from those of other amine dehydrogenases and amine oxidases that use tryptophylquinone and tyrosylquinone cofactors.

The Rv2633c protein of Mycobacterium tuberculosis is a non-heme di-iron catalase with a possible role in defenses against oxidative stress

The Rv2633c gene in Mycobacterium tuberculosis is rapidly up-regulated after macrophage infection, suggesting that Rv2633c is involved in M. tuberculosis pathogenesis. However, the activity and role of the Rv2633c protein in host colonization is unknown. Here, we analyzed the Rv2633c protein sequence, which revealed the presence of an HHE cation-binding domain common in hemerythrin-like proteins. Phylogenetic analysis indicated that Rv2633c is a member of a distinct subset of hemerythrin-like proteins exclusive to mycobacteria. The Rv2633c sequence was significantly similar to protein sequences from other pathogenic strains within that subset, suggesting that these proteins are involved in mycobacteria virulence. We expressed and purified the Rv2633c protein in Escherichia coli and found that it contains two iron atoms, but does not behave like a hemerythrin. It migrated as a dimeric protein during size-exclusion chromatography. It was not possible to reduce the protein or observe any evidence for its interaction with O₂ However, Rv2633c did exhibit catalase activity with a k_cat of 1475 s^-1 and K_m of 10.1 ± 1.7 mm Cyanide and azide inhibited the catalase activity with K_i values of 3.8 μm and 37.7 μm, respectively. Rv2633c's activity was consistent with a role in defenses against oxidative stress generated during host immune responses after M. tuberculosis infection of macrophages. We note that Rv2633c is the first example of a non-heme di-iron catalase, and conclude that it is a member of a subset of hemerythrin-like proteins exclusive to mycobacteria, with likely roles in protection against host defenses.

Roles of Copper and a Conserved Aspartic Acid in the Autocatalytic Hydroxylation of a Specific Tryptophan Residue during Cysteine Tryptophylquinone Biogenesis

The first posttranslational modification step in the biosynthesis of the tryptophan-derived quinone cofactors is the autocatalytic hydroxylation of a specific Trp residue at position C-7 on the indole side chain. Subsequent modifications are catalyzed by modifying enzymes, but the mechanism by which this first step occurs is unknown. LodA possesses a cysteine tryptophylquinone (CTQ) cofactor. Metal analysis as well as spectroscopic and kinetic studies of the mature and precursor forms of a D512A LodA variant provides evidence that copper is required for the initial hydroxylation of the precursor protein and that if alternative metals are bound, the modification does not occur and the precursor is unstable. It is shown that the mature native LodA also contains loosely bound copper, which affects the visible absorbance spectrum and quenches the fluorescence spectrum that is attributed to the mature CTQ cofactor. When copper is removed, the fluorescence appears, and when it is added back to the protein, the fluorescence is quenched, indicating that copper reversibly binds in the proximity of CTQ. Removal of copper does not diminish the enzymatic activity of LodA. This distinguishes LodA from enzymes with protein-derived tyrosylquinone cofactors in which copper is present near the cofactor and is absolutely required for activity. Mechanisms are proposed for the role of copper in the hydroxylation of the unactivated Trp side chain. These results demonstrate that the reason that the highly conserved Asp512 is critical for LodA, and possibly all tryptophylquinone enzymes, is not because it is required for catalysis but because it is necessary for CTQ biosynthesis, more specifically to facilitate the initial copper-dependent hydroxylation of a specific Trp residue.

Analytical Methods for Assessing the Effects of Site-Directed Mutagenesis on Protein-Cofactor and Protein-Protein Functional Relationships

To completely understand the role of an amino acid residue that is targeted for site-directed mutagenesis a thorough analysis of the impact that the mutation has on the function of the protein is required. General methods for performing site-directed mutagenesis and expressing the recombinant protein variant are described. Protein-cofactor interactions are important because cofactors are often directly involved in facilitating catalysis by enzymes and in electron transfer by redox proteins. Many cofactors also have characteristic spectroscopic properties. As such, general methods are described to analyze the spectroscopic, redox and catalytic properties of protein-bound cofactors. Methods for assessing the effects of a mutation on protein-protein interactions are also described. Lastly, methods for assessing the overall structural integrity of the protein are described, as this is important to ensure that the mutation has not caused a global disruption of protein structure, rather than a specific effect on function.

Roles of Conserved Residues of the Glycine Oxidase GoxA in Controlling Activity, Cooperativity, Subunit Composition, and Cysteine Tryptophylquinone Biosynthesis

GoxA is a glycine oxidase that possesses a cysteine tryptophylquinone (CTQ) cofactor that is formed by posttranslational modifications that are catalyzed by a modifying enzyme GoxB. It is the second known tryptophylquinone enzyme to function as an oxidase, the other being the lysine ϵ-oxidase, LodA. All other enzymes containing CTQ or tryptophan tryptophylquinone (TTQ) cofactors are dehydrogenases. Kinetic analysis of GoxA revealed allosteric cooperativity for its glycine substrate, but not O₂ This is the first CTQ- or TTQ-dependent enzyme to exhibit cooperativity. Here, we show that cooperativity and homodimer stabilization are strongly dependent on the presence of Phe-237. Conversion of this residue, which is a Tyr in LodA, to Tyr or Ala eliminates the cooperativity and destabilizes the dimer. These mutations also significantly affect the k_cat and K_m values for the substrates. On the basis of structural and modeling studies, a mechanism by which Phe-237 exerts this influence is presented. Two active site residues, Asp-547 and His-466, were also examined and shown by site-directed mutagenesis to be critical for CTQ biogenesis. This result is compared with the results of similar studies of mutagenesis of structurally conserved residues of other tryptophylquinone enzymes. These results provide insight into the roles of specific active-site residues in catalysis and CTQ biogenesis, as well as describing an interesting mechanism by which a single residue can dictate whether or not an enzyme exhibits cooperative allosteric behavior toward a substrate.

Interaction of GoxA with Its Modifying Enzyme and Its Subunit Assembly Are Dependent on the Extent of Cysteine Tryptophylquinone Biosynthesis

GoxA is a glycine oxidase bearing a protein-derived cysteine tryptophylquinone (CTQ) cofactor that is formed by posttranslational modifications catalyzed by a flavoprotein, GoxB. Two forms of GoxA were isolated: an active form with mature CTQ and an inactive precursor protein that lacked CTQ. The active GoxA was present as a homodimer with no detectable affinity for GoxB, whereas the precursor was isolated as a monomer in a tight complex with one GoxB. Thus, the interaction of GoxA with GoxB and subunit assembly of mature GoxA are each dependent on the extent of CTQ biosynthesis.

Roles of active site residues in LodA, a cysteine tryptophylquinone dependent ε-lysine oxidase

Site-directed mutagenesis identified residues in the substrate channel of LodA that play multiple roles in regulating Km values of substrates, kcat and the extent of biosynthesis of the protein-derived cysteine tryptophylquinone (CTQ) cofactor. Mutations of Cys448 increase Km values for lysine and O2, with the larger effect on Klysine. Tyr211 resides within a mobile loop and is seen in the crystal structure of LodA to form a hydrogen bond with Lys530 that appears to stabilize its position in the channel. Y211F LodA had reduced levels of CTQ but near normal levels of kcat. K530A and K530R variants exhibited diminished levels of CTQ but significantly increased kcat. The Y211F, K530A and K530R mutations each caused large increases in the Km values for lysine and O2. These effects of the mutations of Tyr211 and Lys530 suggest that when these residues are hydrogen-bonded they may form a gate that controls entry and exit of substrates and products from the active site. Y211A and Y211E variants had the highest level of CTQ but exhibited no activity. These results highlight the different evolutionary factors that must be considered for enzymes which possess protein-derived cofactors, in which the catalytic cofactor must be generated by posttranslational modifications.

Site-directed mutagenesis of Gln103 reveals the influence of this residue on the redox properties and stability of MauG

The diheme enzyme MauG catalyzes a six-electron oxidation that is required for the posttranslational modification of a precursor of methylamine dehydrogenase (preMADH) to complete the biosynthesis of its protein-derived cofactor, tryptophan tryptophylquinone (TTQ). Crystallographic and computational studies have implicated Gln103 in stabilizing the Fe^IV=O moiety of the bis-Fe^IV state by hydrogen bonding. The role of Gln103 was probed by site-directed mutagenesis. Q103L and Q103E mutations resulted in no expression and very little expression of the protein, respectively. Q103A MauG exhibited oxidative damage when isolated. Q103N MauG was isolated at levels comparable to that of wild-type MauG and exhibited normal activity in catalyzing the biosynthesis of TTQ from preMADH. The crystal structure of the Q103N MauG–preMADH complex suggests that a water may mediate hydrogen bonding between the shorter Asn103 side chain and the Fe^IV=O moiety. The Q103N mutation caused the two redox potentials associated with the diferric/diferrous redox couple to become less negative, although the redox cooperativity of the hemes of MauG was retained. Upon addition of H₂O₂, Q103N MauG exhibits changes in the absorbance spectrum in the Soret and near-IR regions consistent with formation of the bis-Fe^IV redox state. However, the rate of spontaneous return of the spectrum in the Soret region was 4.5-fold greater for Q103N MauG than for wild-type MauG. In contrast, the rate of spontaneous decay of the absorbance at 950 nm, which is associated with charge-resonance stabilization of the high-valence state, was similar for wild-type MauG and Q103N MauG. This suggests that as a consequence of the mutation a different distribution of resonance structures stabilizes the bis-Fe^IV state. These results demonstrate that subtle changes in the structure of the side chain of residue 103 can significantly affect the overall protein stability of MauG and alter the redox properties of the hemes.

Steady-state kinetic mechanism of LodA, a novel cysteine tryptophylquinone-dependent oxidase

LodA is a novel lysine-ε-oxidase which possesses a cysteine tryptophylquinone cofactor. It is the first tryptophylquinone enzyme known to function as an oxidase. A steady-state kinetic analysis shows that LodA obeys a ping-pong kinetic mechanism with values of kcat of 0.22±0.04 s(-1), Klysine of 3.2±0.5 μM and KO2 of 37.2±6.1 μM. The kcat exhibited a pH optimum at 7.5 while kcat/Klysine peaked at 7.0 and remained constant to pH 8.5. Alternative electron acceptors could not effectively substitute for O2 in the reaction. A mechanism for the reductive half reaction of LodA is proposed that is consistent with the ping-pong kinetics.

Binding of Cu(II) complexes of oxicam NSAIDs to alternating AT and homopolymeric AT sequences: differential response to variation in backbone structure

Besides their principal functions as painkillers and anti-inflammatory agents, drugs belonging to the nonsteroidal anti-inflammatory drug (NSAID) group also have anticancer properties. Cu(II) complexes of these drugs enhance the anticancer effect. How they exert this effect is not clear. As a possible molecular mechanism, our group has already shown that the Cu(II) complexes of two oxicam NSAIDs with anticancer properties, viz. piroxicam and meloxicam, can directly bind to the DNA backbone. AT stretches are abundant in the eukaryotic genome. These stretches are more accessible to binding of different ligands, resulting in expression of different functions. AT stretches containing both alternating base pairs and homopolymeric bases in individual strands show subtle differences in backbone structures. It is therefore of interest to see how the Cu(II)-NSAID complexes respond to such differences in backbone structure. Binding studies of these complexes with alternating polydA-dT and homopolymeric polydA-polydT have been conducted using UV-vis absorption titration studies, UV melting studies and circular dichroism spectroscopy. Competitive binding with the standard intercalator ethidium bromide and the minor groove binder 4',6-diamidino-2-phenylindole was monitored using fluorescence to identify the possible binding mode. Our results show that Cu(II)-NSAID complexes are highly sensitive to the subtle differences in backbone structures of polydA-dT and polydA-polydT and respond to them by exhibiting different binding properties, such as binding constants, effect on duplex stability and binding modes. Both complexes have a similar binding mode with polydA-dT, which is intercalative, but for polydA-polydT, the results point to a mixed mode of binding.