Characterization of E121K mutation of D-amino acid oxidase - Insights into mechanisms leading to amyotrophic lateral sclerosis

Activity assays for flavoprotein oxidases: an overview

Flavoprotein oxidases have found many biotechnological applications. For identifying and improving their characteristics, it is essential to have reliable and robust assay methodology available. The methodologies used to monitor their activity seem to be scattered in the literature and seem often selected based on convenience. Due to the diversity of reactions catalyzed by flavoprotein oxidases, it is virtually impossible to recommend a single activity assay. A literature analysis of 60 recent papers describing flavoprotein oxidases revealed that continuous spectrophotometric assays, in particular colorimetric assays, are the preferred choice, as they are facile, scalable and allow for better interpretation of data than discontinuous assays. Colorimetric assays typically rely on the extinction coefficient of a monitored chromogenic product, which can be highly variable depending on the experimental conditions. Therefore, it is important to determine the extinction coefficient under the specific experimental conditions used, rather than taking it directly from the literature. To provide a guideline and assist in standardization, this review describes the most commonly utilized activity assays for flavoprotein oxidases, along with their respective merits and limitations. KEY POINTS: • Researchers should be more aware of limitations of activity assays. • Extinction coefficients should be determined for the appropriate experimental setup. • New robust activity assays are desired.

Comorbidity of Histamine Intolerance and Polyvalent Allergy: A Case Report and Literature Review

Background/Objectives: Histamine intolerance is becoming a critical medical problem across numerous clinical specialties, due to the absence of a standardized diagnostic and therapeutic strategy to manage patients with a suspicion of or diagnosis of this condition. Histamine intolerance is a type of non-immune food hypersensitivity, characterized by heterogenous etiologies and a very broad range of symptoms. The condition is the result of an imbalance between the amount of histamine accumulated within the body and the body's systemic ability to degrade it. In regard to the diagnostics of histamine intolerance, the need to preliminarily exclude other potential conditions associated with increased histamine levels in the blood has been highlighted. The co-occurrence of allergies and histamine intolerance is not uncommon, and the similarity of the clinical manifestations can lead to diagnostic, as well as therapeutic, difficulties. This paper details the diagnostic and clinical workflow for a patient with histamine intolerance and polyvalent allergy comorbidity, with the aim being to help outline a protocol that may be helpful to clinicians managing patients with histamine intolerance. Case Presentation: This article presents the case of a 30-year-old patient with a polyvalent allergy and multimorbidity (allergic rhinitis, asthma, a food allergy, and eosinophilic esophagitis), with comorbid histamine intolerance. Due to the violent and severe symptoms, including facial erythema, urticaria, pruritus, abdominal pain, and tachycardia, experienced after meals, the patient received intramuscular epinephrine injections three times a week. The diagnostic protocol and the course of therapeutic management are presented. Conclusions: The diagnosis of histamine intolerance is difficult due to the high variability and heterogeneity of clinical symptoms in individual patients. Many studies on the issue recommend ruling out an allergic background in terms of the complaint. However, the possibility of the symptoms of an IgE-dependent allergy overlapping with those of histamine intolerance should be taken into account in every case. This is particularly important in patients presenting with an atypical and severe course of allergic diseases. The clinical case presented herein may be helpful for the daily practice of allergologists and physicians with other specialties, as an example of multimorbidity with both allergic and non-allergic backgrounds.

Aggregation of E121K mutant D-amino acid oxidase and ubiquitination-mediated autophagy mechanisms leading to amyotrophic lateral sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a terminal adult-onset neuromuscular disorder. Our group has been studying this illness and previously reported novel mutations and rare mutations in a study using next-generation sequencing of DNA samples from Indian ALS patients. In this paper, we focus on the E121K mutation in the DAO gene to understand how it leads to ALS. Our experiments in SH-SY5Y cells indicate that the E121K mutation results in the accumulation of mutant protein aggregates, a change in cell morphology, and the death of neuronal cells. These protein aggregates get ubiquitinated and cause an imbalance in autophagy regulation. We observed an increase in the cellular concentrations of p62, OPTN, and LC3II. Through confocal microscopy studies, we show that the binding of p62 with ubiquitinated aggregates and its recruitment to LC3II mediates autophagosome generation. These relative changes in the key partners in autophagy increase cell death in cells harboring the E121K mutation and is a probable mechanism leading to ALS.

Structural and mechanistic insights into ALS patient derived mutations in D-amino acid oxidase

The D-amino acid oxidase protein modulates neurotransmission by controlling the levels of D-serine, a co-agonist of N-methyl-D-aspartate receptors. Mutations in the DAO gene have been associated with ALS, with some studies reporting pathogenic mechanisms of the R199W mutation. We have characterized two novel mutations R38H and Q201R found in ALS patients and report certain novel findings related to the R199W mutation. We report the first instance of crystal structure analysis of a patient-derived mutant of DAO, R38H, solved at 2.10 Å. The structure revealed significant perturbations and altered binding with the cofactor (FAD) and the inhibitor benzoate, supported by biochemical assays. Q201R-DAO also exhibited significantly lower ligand binding efficiency. Furthermore, kinetic analysis across all variants revealed reduced oxidase activity and substrate binding. Notably, R38H-DAO exhibited near-WT activity only at high substrate concentrations, while R199W-DAO and Q201R-DAO displayed drastic activity reduction. Additionally, structural perturbations were inferred for R199W-DAO and Q201R-DAO, evident by the higher oligomeric state in the holoenzyme form. We also observed thermal instability in case of R199W-DAO mutant. We hypothesize that the mutant enzymes may be rendered non-functional in a cellular context, potentially leading to NMDAR-associated excitotoxicity. The study provides novel insights into structural and functional aspects of DAO mutations in ALS.