Human carbonic anhydrase II catalyzes the reversible reaction of carbon dioxide and water to form bicarbonate and a proton. His64-mediated proton shuttling between the active site and the bulk solvent is rate limiting. Here we investigate the protonation behavior of His64 as well as its structural and dynamic features in a pH dependent way. We derive two pK_a values for His64, 6.25 and 7.60, that we were able to assign to its inward and outward conformation. Furthermore, we show that His64 exists in both conformations equally, independent of pH. Both conformations display an equal distribution of their two neutral tautomeric states. The life time of each conformation is short and both states display high flexibility within their orientation. Therefore, His64 is never static, but rather poised to change conformation. These findings support an energetic, dynamic and solution ensemble-based framework for the high enzymatic activity of human carbonic anhydrase II.

Introduction: Motor impairments are the objectively most striking sequelae after stroke, but non-motor consequences represent a high burden for stroke survivors as well. Depression is reported in one third of patients, the fatigue prevalence ranges from 23 to 75% due to heterogenous definitions and assessments. Cognitive impairment is found in one third of stroke patients 3–12 months after stroke and the risk for dementia is doubled by the event. Aerobic exercise has been shown to reduce depressive symptoms, counteract fatigue, and improve cognitive functions in non-stroke patients. Furthermore, exercise is known to strengthen the immune system. It is unknown, though, if aerobic exercise can counteract poststroke depression, fatigue, poststroke dementia and poststroke immunosuppression. Therefore, we aim to analyse the effect of aerobic exercise on functional recovery, cognition, emotional well-being, and the immune system. Reorganization of topological networks of the brain shall be visualized by diffusion MRI fibre tracking. Methods: Adults with mild to moderate stroke impairment (initial NIHSS or NIHSS determined at the moment of maximal deterioration 1–18) are recruited within two weeks of stroke onset. Study participants must be able to walk independently without risk of falling. All patients are equipped with wearable devices (smartwatches) measuring the heart rate and daily step count. The optimal heart rate zone is determined by lactate ergometry at baseline. Patients are randomized to the control or the intervention group, the latter performing a heart rate-controlled walking training on own initiative 5 times a week for 45 min. All patients receive medical care and stroke rehabilitation to the usual standard of care. The following assessments are conducted at baseline and after 90 days: Fugl Meyer-assessment for the upper and lower extremity, 6 min-walk test, neuropsychological assessment (cognition: MoCA, SDMT; fatigue and depression: FSMC, HADS-D, participation: WHODAS 2.0 12-items), blood testing (i.e. immune profiling to obtain insights into phenotype and functional features of distinct immune-cell subsets) and cranial magnetic resonance imaging (MRI) with grid-sampled diffusion weighted imaging, white matter fibre tracking and MR spectroscopy. Perspective: This study investigates the effect of smartwatch-controlled aerobic exercise on functional recovery, cognition, emotional well-being, the immune system, and neuronal network reorganization in stroke patients. Trial registration ClinicalTrials.gov NCT Number: NCT05690165. First posted19 January 2023. Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT05690165

Histidine is a key amino‐acid residues in proteins that can exist in three different protonation states: two different neutral tautomeric forms and a protonated, positively charged one. It can act as both donor and acceptor of hydrogen bonds, coordinate metal ions, and engage in acid/base catalysis. Human Carbonic Anhydrase II (HCA II) is a pivotal enzyme catalyzing the reversible hydration of carbon dioxide. It contains 12 histidine residues: six are surface exposed, two buried, three are active site zinc ion ligands, and one is a proton shuttle. Comparing results from NMR spectroscopy with previously determined neutron protein crystal structures enabled a side‐by‐side investigation of the proton occupancies and preferred tautomeric states of the histidine residues in HCA II. Buried and zinc coordinating histidines remain in one neutral tautomeric state across the entire pH range studied, as validated by both methods. In contrast, solvent‐exposed histidines display high variability in proton occupancies. While the data were overall remarkably consistent between methods, some discrepancies were observed, shedding light on the limitations of each technique. Therefore, combining these methods with full awareness of the advantages and drawbacks of each, provides insights into the dynamic protonation landscape of HCA II histidines, crucial for elucidating enzyme catalytic mechanisms.

The mutated enzyme isocitrate dehydrogenase (IDH) 1 and 2 has been detected in various tumor entities such as gliomas and can convert α-ketoglutarate into the oncometabolite 2-hydroxyglutarate (2-HG). This neuro-oncologically significant metabolic product can be detected by MR spectroscopy and is therefore suitable for noninvasive glioma classification and therapy monitoring. This paper provides an up-to-date overview of the methodology and relevance of ¹H-MR spectroscopy (MRS) in the oncological primary and follow-up diagnosis of gliomas. The possibilities and limitations of this MR spectroscopic examination are evaluated on the basis of the available literature. By detecting 2-HG, MRS can in principle offer a noninvasive alternative to immunohistological analysis thus avoiding surgical intervention in some cases. However, in addition to an adapted and optimized examination protocol, the individual measurement conditions in the examination region are of decisive importance. Due to the inherently small signal of 2-HG, unfavorable measurement conditions can influence the reliability of detection. Received: 28 November 2023 Accepted after revision: 04 March 2024 Article published online: 22 April 2024 © 2024. Thieme. All rights reserved. Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Background: Thyroid nodules are highly prevalent, affecting up to 75% of the population, yet most are benign. The limited specificity of ultrasound-based workup leads to substantial overdiagnosis and overtreatment, underscoring the need for improved imaging-based classification. Diffusion-weighted MRI (DWI), quantified via the apparent diffusion coefficient (ADC), has emerged as a promising imaging biomarker. This meta-analysis updates pooled diagnostic performance metrics and systematically evaluates which DWI acquisition techniques, imaging parameters, and combinations with other MRI modalities are most promising for clinical translation. Methods: PubMed, Web of Science, Scopus, and ProQuest were systematically searched. Pooled sensitivity, specificity, and area under the curve (AUC) were calculated using bivariate random-effects models. The effects of b-value, magnetic field strength, echo time, and diffusion model on diagnostic accuracy and ADC values were examined through subgroup and meta-regression analyses. Results: Forty-six studies (3003 nodules) were included. Pooled sensitivity and specificity were 0.84 (95% CI: 0.81–0.86) and 0.88 (95% CI: 0.85–0.90), with an AUC of 0.912. Intravoxel incoherent motion and diffusion kurtosis imaging showed no added value over the mono-exponential model. For the mono-exponential model, a negative association between b-values and reported ADCs was observed, whereas no association was found between b-values and diagnostic accuracy. Magnetic field strength and echo time did not affect ADCs. Combining DWI with morphological imaging showed the potential to further enhance diagnostic performance. Conclusions: DWI holds strong potential to improve the diagnostic workup of thyroid nodules. Technical standardization, particularly of key acquisition parameters, should be pursued to enable clinical implementation.