Amino acid positions near the active site determine the reduced activity of human ACOD1 compared to murine ACOD1.

cis-Aconitate decarboxylase (ACOD1, IRG1) converts cis-aconitate to the immunomodulatory and antibacterial metabolite itaconate. Although the active site residues of human and mouse ACOD1 are identical, the mouse enzyme is about fivefold more active. Aiming to identify the cause of this difference, we mutated positions near the active site in human ACOD1 to the corresponding residues of mouse ACOD1 and measured resulting activities in vitro and in transfected cells. Interestingly, Homo sapiens is the only species with methionine instead of isoleucine at residue 154 and introduction of isoleucine at this position increased the activity of human ACOD1 1.5-fold in transfected cells and 3.5-fold in vitro. Enzyme activity of gorilla ACOD1, which is almost identical to the human enzyme but has isoleucine at residue 154, was similar to the mouse enzyme in vitro. Met154 in human ACOD1 forms a sulfur-π bond to Phe381, which is positioned to impede access of the substrate to the active site. It appears that the ACOD1 sequence has changed at position 154 during human evolution, resulting in a pronounced decrease in activity. This change might have offered a selective advantage in diseases such as cancer.

SARS-CoV-2-Specific Antibody Prevalence and Symptoms in a Local Austrian Population.

Background: Since December 2019 the novel coronavirus (SARS-CoV-2) is the center of global attention due to its rapid transmission and toll on health care systems and global economy. Population-based serosurveys measuring antibodies for SARS-CoV-2 provide one method for estimating previous infection rates including the symptom-free courses of the disease and monitoring the progression of the epidemic. Methods: In June 2020 we succeeded in testing almost half of the population of an Austrian township (1,359 inhabitants) with a reported higher incidence for COVID-19 infections (17 PCR positive cases have been officially reported until the date of sample collection, i.e., 1.2% of the total population). We determined the prevalence of SARS-CoV-2-specific antibodies in this population, factors affecting, and symptoms correlated with prior infection. Antibodies were determined using a CE-certified quality-controlled ELISA test for SARS-CoV-2-specific IgG and IgA antibodies. Results: We found a high prevalence of 9% positive antibodies among the town population in comparison to 6% of the neighboring villages. This was considerably higher than the officially known RT-PCR-approved COVID-19 cases (1.2%) in the town population. Twenty percent of SARS-CoV-2-antibody positive cases declared being asymptomatic in a questionnaire. On the other hand, we identified six single major symptoms, including anosmia/ageusia, weight loss, anorexia, general debility, dyspnea, and fever, and especially their combination to be of high prognostic value for predicting SARS-CoV-2 infection in a patient. Conclusions: This population study demonstrated a high prevalence of antibodies to SARS-CoV-2 as a marker of past infections in an Austrian township. Several symptoms revealed a diagnostic value especially in combination.