Adolescent Reference Values for MR-Derived Biventricular Strain Obtained Using Feature-Tracking and Myocardial Tagging.

BACKGROUND: Myocardial strain is a promising marker for the detection of early left or right ventricular (LV or RV) dysfunction in pediatric populations. The reference standard for MR strain measurement is myocardial tagging (MT); however, MT has limited clinical utility because the additional acquisitions needed are time-consuming. In contrast, MR-feature tracking (FT) allows strain quantification from routinely acquired cine sequences. Studies providing reference values obtained with both FT and MT for adolescents are lacking. PURPOSE: To use MR-FT and MT to define sex-specific LV and RV strain reference values for adolescents. STUDY TYPE: Cross-sectional, prospective. POPULATION: One hundred twenty-three adolescents aged 15-18 years (52% girls) without known cardiovascular disease. FIELD STRENGTH/SEQUENCE: Balanced steady-state free-precession sequence for FT analysis and a spatial modulation of magnetization hybrid TFE-EPI sequence for MT acquisitions at 3.0-T. ASSESSMENT: Segment Medviso software was used to obtain longitudinal (LS) and circumferential (CS) strain for both ventricles, and radial strain (RS) for LV. STATISTICAL TESTS: The Student t-test was used for between-sex comparisons of continuous variables. Sex-specific percentiles were calculated using the weighted average method. Intraobserver and interobserver agreement was assessed in 30 randomly selected studies using intraclass correlation coefficients (ICC). A P-value <0.05 was considered statistically significant. RESULTS: FT-derived LVLS and LVCS were significantly higher in girls than in boys (-19.8% vs. -17.8% and -22.2% vs. -21.0%, respectively), as they were with MT (LVLS: -18.1% vs. -16.8%; LVCS: -20.8% vs. -19.7%). FT-LVRS was higher in girls than in boys (44.8% vs. 35.1%), while MT-LVRS was the opposite (18.6% vs. 22.7%). FT-RVLS was higher in girls (-23.4% vs. -21.3%), but there were no between-sex differences in MT-derived RVLS or RVCS. ICC values for intraobserver agreement were ≥0.89, whereas for interobserver agreement were <0.80 for MT-LVRS and ≥0.80 for all remaining parameters. DATA CONCLUSION: This study provides sex-specific reference biventricular strain values obtained with MR-MT and MR-FT for adolescents aged 15-18 years. MR-FT may be a valid method for obtaining strain values in pediatric populations. EVIDENCE LEVEL: 1 TECHNICAL EFFICACY: Stage 3.

The sequence context in poly-alanine regions: structure, function and conservation.

MOTIVATION: Poly-alanine (polyA) regions are protein stretches mostly composed of alanines. Despite their abundance in eukaryotic proteomes and their association to nine inherited human diseases, the structural and functional roles exerted by polyA stretches remain poorly understood. In this work we study how the amino acid context in which polyA regions are settled in proteins influences their structure and function. RESULTS: We identified glycine and proline as the most abundant amino acids within polyA and in the flanking regions of polyA tracts, in human proteins as well as in 17 additional eukaryotic species. Our analyses indicate that the non-structuring nature of these two amino acids influences the α-helical conformations predicted for polyA, suggesting a relevant role in reducing the inherent aggregation propensity of long polyA. Then, we show how polyA position in protein N-termini relates with their function as transit peptides. PolyA placed just after the initial methionine is often predicted as part of mitochondrial transit peptides, whereas when placed in downstream positions, polyA are part of signal peptides. A few examples from known structures suggest that short polyA can emerge by alanine substitutions in α-helices; but evolution by insertion is observed for longer polyA. Our results showcase the importance of studying the sequence context of homorepeats as a mechanism to shape their structure-function relationships. AVAILABILITY AND IMPLEMENTATION: The datasets used and/or analyzed during the current study are available from the corresponding author onreasonable request. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

Proposed mechanism for regulation of H2 O2 -induced programmed cell death in plants by binding of cytochrome c to 14-3-3 proteins.

Programmed cell death (PCD) is crucial for development and homeostasis of all multicellular organisms. In human cells, the double role of extra-mitochondrial cytochrome c in triggering apoptosis and inhibiting survival pathways is well reported. In plants, however, the specific role of cytochrome c upon release from the mitochondria remains in part veiled yet death stimuli do trigger cytochrome c translocation as well. Here, we identify an Arabidopsis thaliana 14-3-3ι isoform as a cytosolic cytochrome c target and inhibitor of caspase-like activity. This finding establishes the 14-3-3ι protein as a relevant factor at the onset of plant H2 O2 -induced PCD. The in vivo and in vitro studies herein reported reveal that the interaction between cytochrome c and 14-3-3ι exhibits noticeable similarities with the complex formed by their human orthologues. Further analysis of the heterologous complexes between human and plant cytochrome c with plant 14-3-3ι and human 14-3-3ε isoforms corroborated common features. These results suggest that cytochrome c blocks p14-3-3ι so as to inhibit caspase-like proteases, which in turn promote cell death upon H2 O2 treatment. Besides establishing common biochemical features between human and plant PCD, this work sheds light onto the signaling networks of plant cell death.

Oxidative stress is tightly regulated by cytochrome c phosphorylation and respirasome factors in mitochondria.

Respiratory cytochrome c has been found to be phosphorylated at tyrosine 97 in the postischemic brain upon neuroprotective insulin treatment, but how such posttranslational modification affects mitochondrial metabolism is unclear. Here, we report the structural features and functional behavior of a phosphomimetic cytochrome c mutant, which was generated by site-specific incorporation at position 97 of p-carboxymethyl-l-phenylalanine using the evolved tRNA synthetase method. We found that the point mutation does not alter the overall folding and heme environment of cytochrome c, but significantly affects the entire oxidative phosphorylation process. In fact, the electron donation rate of the mutant heme protein to cytochrome c oxidase, or complex IV, within respiratory supercomplexes was higher than that of the wild-type species, in agreement with the observed decrease in reactive oxygen species production. Direct contact of cytochrome c with the respiratory supercomplex factor HIGD1A (hypoxia-inducible domain family member 1A) is reported here, with the mutant heme protein exhibiting a lower affinity than the wild-type species. Interestingly, phosphomimetic cytochrome c also exhibited a lower caspase-3 activation activity. Altogether, these findings yield a better understanding of the molecular basis for mitochondrial metabolism in acute diseases, such as brain ischemia, and thus could allow the use of phosphomimetic cytochrome c as a neuroprotector with therapeutic applications.

Evidence of the Reduced Abundance of Proline cis Conformation in Protein Poly Proline Tracts.

Proline is found in a cis conformation in proteins more often than other proteinogenic amino acids, where it influences structure and modulates function, being the focus of several high-resolution structural studies. However, until now, technical and methodological limitations have hampered the site-specific investigation of the conformational preferences of prolines present in poly proline (poly-P) homorepeats in their protein context. Here, we apply site-specific isotopic labeling to obtain high-resolution NMR data on the cis/trans equilibrium of prolines within the poly-P repeats of huntingtin exon 1, the causative agent of Huntington's disease. Screening prolines in different positions in long (poly-P11) and short (poly-P3) poly-P tracts, we found that, while the first proline of poly-P tracts adopts similar levels of cis conformation as isolated prolines, a length-dependent reduced abundance of cis conformers is observed for terminal prolines. Interestingly, the cis isomer could not be detected in inner prolines, in line with percentages derived from a large database of proline-centered tripeptides extracted from crystallographic structures. These results suggest a strong cooperative effect within poly-Ps that enhances their stiffness by diminishing the stability of the cis conformation. This rigidity is key to rationalizing the protection toward aggregation that the poly-P tract confers to huntingtin. Furthermore, the study provides new avenues to probe the structural properties of poly-P tracts in protein design as scaffolds or nanoscale rulers.

Site-Specific Isotopic Labeling (SSIL): Access to High-Resolution Structural and Dynamic Information in Low-Complexity Proteins.

Remarkable technical progress in the area of structural biology has paved the way to study previously inaccessible targets. For example, large protein complexes can now be easily investigated by cryo-electron microscopy, and modern high-field NMR magnets have challenged the limits of high-resolution characterization of proteins in solution. However, the structural and dynamic characteristics of certain proteins with important functions still cannot be probed by conventional methods. These proteins in question contain low-complexity regions (LCRs), compositionally biased sequences where only a limited number of amino acids is repeated multiple times, which hamper their characterization. This Concept article describes a site-specific isotopic labeling (SSIL) strategy, which combines nonsense suppression and cell-free protein synthesis to overcome these limitations. An overview on how poly-glutamine tracts were made amenable to high-resolution structural studies is used to illustrate the usefulness of SSIL. Furthermore, we discuss the potential of this methodology to give further insights into the roles of LCRs in human pathologies and liquid-liquid phase separation, as well as the challenges that must be addressed in the future for the popularization of SSIL.

A method for studying the influence of Mn oxyhydroxides on the trace element content of aquatic bryophytes.

The main objective of this study was to develop and test a method of separating externally deposited Mn oxyhydroxides and co-precipitated elements from samples of aquatic moss (the moss Fontinalis antipyretica). The method, which uses 0.1 M hydroxylamine to dissolve the oxyhydroxides, was tested with samples collected in rivers with slightly acidic, well­oxygenated waters, where high rates of Mn precipitation occur. The method was effective (it extracted up to 84 % of the Mn) and selective (Fe oxyhydroxides were not extracted). The elements Ba, Cd, Zn and Ni were associated with the Mn oxyhydroxides, while Al, As, Cr, Cu, Fe, Hg and Pb were not. Deposition of Mn therefore increased the concentration of some elements in the moss samples. However, as Mn precipitation depends on Eh and pH, which are independent of the concentrations of the elements in water, the relationship between water and moss element concentrations is not clear (i.e. the data are noisy). This is a problem in biomonitoring studies, which assume a close relationship between element concentrations in moss and water. The value of the proposed extraction method is that it can be used to correct the effect of Mn deposition. We present an example of this correction applied to the Cd concentrations in the test data. We found that the noise introduced by the Mn, including age-related effects (observed by comparing concentrations in 0-2.5 and 2.2-5.0 cm sections from the shoot apex), can be reduced. Additionally, the correction revealed recent increases in Cd concentrations in one site that were not observed in the uncorrected data. Another finding of interest was the low content of total Mn and different extractability (of most elements) observed in moss samples collected in alkaline waters. Finally, we discuss how future studies designed for different environmental scenarios can benefit from application of the proposed method.

Absence of Myocardial Involvement After SARS-CoV-2 Vaccination in Asymptomatic Adolescents.

This study aimed to evaluate the presence of subclinical myocardial damage in adolescents who were vaccinated against SARS-CoV-2. One hundred twenty asymptomatic adolescents with a mean age of 16.0 ± 0.4 years (51% girls) underwent cardiac magnetic resonance (CMR) imaging. SARS-CoV-2 IgG/IgM antibody testing was performed, and self-reported dates of confirmed SARS-CoV-2 infection and/or vaccination were collected. Participants were classified according to SARS-CoV-2 status as naïve (non-infected and unvaccinated, n = 74), infected (unvaccinated, n = 23), and vaccinated (independently of past infection status, n = 23). Biventricular volumes and ejection fraction and myocardial T2 relaxation time were similar in the three groups. T1 relaxation time was slightly higher in vaccinated adolescents (1249 ± 35 ms) than in naïve and infected participants (1231 ± 30 ms and 1227 ± 29 ms, respectively; p = 0.035), although this difference was considered clinically irrelevant. This observational study found no evidence of relevant subclinical myocardial involvement after SARS-CoV-2 vaccination in asymptomatic adolescents.

An extended interaction site determines binding between AP180 and AP2 in clathrin mediated endocytosis.

The early phases of clathrin mediated endocytosis are organized through a highly complex interaction network mediated by clathrin associated sorting proteins (CLASPs) that comprise long intrinsically disordered regions (IDRs). AP180 is a CLASP exclusively expressed in neurons and comprises a long IDR of around 600 residues, whose function remains partially elusive. Using NMR spectroscopy, we discovered an extended and strong interaction site within AP180 with the major adaptor protein AP2, and describe its binding dynamics at atomic resolution. We find that the 70 residue-long site determines the overall interaction between AP180 and AP2 in a dynamic equilibrium between its bound and unbound states, while weaker binding sites contribute to the overall affinity at much higher concentrations of AP2. Our data suggest that this particular interaction site might play a central role in recruitment of adaptors to the clathrin coated pit, whereas more transient and promiscuous interactions allow reshaping of the interaction network until cargo uptake inside a coated vesicle.

Influence of the storage procedure on the trace element content measured in the aquatic moss Fontinalis antipyretica Hedw.

Aquatic bryophytes have been used as pollution biomonitors for decades. Despite this, sample collection and preparation methods have not been standardized, which makes it difficult to compare the results of different studies. Most times, the samples have to be stored before processing, for example, when many of them are collected in a short time, as occurs in extensive pollution studies. Storage must be done in a way that does not change the pollutant concentrations in the samples. We studied whether the concentrations of Al, As, Ba, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, and Zn in the aquatic moss Fontinalis antipyretica were affected by three storage procedures: dry at room temperature, fresh (in refrigerator at 6°C), and frozen at -20°C. In addition, we evaluated whether the subsequent washing of the samples affected the concentrations of these elements differently depending on the storage method. Our results showed that the three methods were, in general, adequate since the concentrations did not change, and we did not observe differences between washed and unwashed samples either. Since the simplest method is refrigeration, we concluded that this is the best of them. However, the concentrations of Hg increased steadily over time in the fresh material, probably because of redistribution after volatilization from the basal parts of the mosses. We believe that the respiration of the plants lowered the concentrations of oxygen inside the hermetically sealed bags containing the samples, thus promoting the reduction of the Hg and its posterior volatilization and redistribution. We did not observe interactions between the storage method and the posterior washing of the samples. PRACTITIONER POINTS: We studied the influence of storage procedure on element content in aquatic mosses. The procedures were as follows: dried at room temperature, stored in refrigerator, and frozen. The procedures did not change the element contents, except for Hg in refrigerator. All the procedures seemed suitable, but refrigeration was the simplest one.

Structure-function relationships in protein homorepeats.

Homorepeats (or polyX), protein segments containing repetitions of the same amino acid, are abundant in proteomes from all kingdoms of life and are involved in crucial biological functions as well as several neurodegenerative and developmental diseases. Mainly inserted in disordered segments of proteins, the structure/function relationships of homorepeats remain largely unexplored. In this review, we summarize present knowledge for the most abundant homorepeats, highlighting the role of the inherent structure and the conformational influence exerted by their flanking regions. Recent experimental and computational methods enable residue-specific investigations of these regions and promise novel structural and dynamic information for this elusive group of proteins. This information should increase our knowledge about the structural bases of phenomena such as liquid-liquid phase separation and trinucleotide repeat disorders.

Incidence, Predictors, and Prognostic Impact of Bleeding Events After TAVR According to VARC-3 Criteria.

BACKGROUND: The updated Valve Academic Research Consortium (VARC) definition for bleeding events after transcatheter aortic valve replacement (TAVR) lacks of clinical validation. OBJECTIVES: The aim of this study was to determine the incidence, predictors, and clinical impact of bleeding events following TAVR as defined by recent VARC-3 criteria. METHODS: A total of 2,384 consecutive patients with severe symptomatic aortic stenosis undergoing TAVR were included. Early (at index hospitalization) and late (after hospital discharge) bleeding complications were defined according to VARC-3 criteria as type 1, 2, 3, or 4. Baseline, procedural, and follow-up (24 [IQR: 12-43] months) data were prospectively collected. RESULTS: Bleeding events occurred in 761 patients (31.9%): types 1, 2, 3, and 4 in 169 (22.2%), 399 (52.4%), 149 (19.6%), and 44 (5.8%) patients, respectively. The primary vascular access site and gastrointestinal locations were the most common bleeding sources among early and late bleeding events, respectively. Female sex, thoracotomy access, larger (14-F) sheath use, and dual antiplatelet therapy determined an increased risk of early bleeding events (P < 0.02 for all). The use of the radial artery for secondary access was associated with a significant risk reduction of early bleeding (P < 0.001). Type 2 and type 3 events were associated with an increased mortality risk at 30-day (HR: 2.94 [95% CI: 1.43-6.03; P = 0.003] and HR: 4.91 [95% CI: 2.19-11.03; P < 0.001], respectively) and 1-year (HR: 1.86 [95% CI: 1.28-2.69; P = 0.001] and HR: 2.28 [95% CI: 1.41-3.66; P = 0.001], respectively) follow-up. A similar prognostic pattern was observed when applying VARC-2 criteria but with a much lower global incidence of early bleeding events (19% vs 27%; P < 0.001). CONCLUSIONS: Bleeding events after TAVR were associated with poorer short- and long-term survival. The magnitude of this correlation was proportional to bleeding severity defined according to VARC-3 criteria. Further studies on bleeding prevention following TAVR are warranted to improve procedural safety and patient prognosis.

Myocardial Injury After Transcatheter Aortic Valve Replacement According to VARC-3 Criteria.

BACKGROUND: The Valve Academic Research Consortium (VARC)-3 definition for myocardial injury after transcatheter aortic valve replacement (TAVR) lacks of clinical validation. OBJECTIVES: This study sought to determine the incidence, predictors, and clinical impact of periprocedural myocardial injury (PPMI) following TAVR as defined by recent VARC-3 criteria. METHODS: We included 1,394 consecutive patients who underwent TAVR with a new-generation transcatheter heart valve. High-sensitivity troponin levels were assessed at baseline and within 24 hours after the procedure. PPMI was defined according to VARC-3 criteria as an increase ≥70 times in troponin levels (vs ≥15 times according to the VARC-2 definition). Baseline, procedural, and follow-up data were prospectively collected. RESULTS: PPMI was diagnosed in 193 (14.0%) patients. Female sex and peripheral artery disease were independent predictors of PPMI (P < 0.01 for both). PPMI was associated with a higher risk of mortality at 30-day (HR: 2.69, 95% CI: 1.50-4.82; P = 0.001) and 1-year (for all-cause mortality, HR: 1.54; 95% CI: 1.04-2.27; P = 0.032; for cardiovascular mortality, HR: 3.04; 95% CI: 1.68-5.50; P < 0.001) follow-up. PPMI according to VARC-2 criteria had no impact on mortality. CONCLUSIONS: About 1 out of 10 patients undergoing TAVR in the contemporary era had PPMI as defined by recent VARC-3 criteria, and baseline factors like female sex and peripheral artery disease determined an increased risk. PPMI had a negative impact on early and late survival. Further studies on the prevention of PPMI post-TAVR and implementing measures to improve outcomes in PPMI patients are warranted.

Angina in patients with severe aortic stenosis undergoing transcatheter aortic valve replacement.

INTRODUCTION AND OBJECTIVES: To evaluate the prevalence, clinical characteristics, and outcomes of patients with angina undergoing transcatheter aortic valve replacement (TAVR) for severe aortic stenosis. METHODS: A total of 1687 consecutive patients with severe aortic stenosis undergoing TAVR at our center were included and classified according to patient-reported angina symptoms prior to the TAVR procedure. Baseline, procedural and follow-up data were collected in a dedicated database. RESULTS: A total of 497 patients (29%) had angina prior to the TAVR procedure. Patients with angina at baseline showed a worse New York Heart Association (NYHA) functional class (NYHA class> II: 69% vs 63%; P=.017), a higher rate of coronary artery disease (74% vs 56%; P <.001), and a lower rate of complete revascularization (70% vs 79%; P <.001). Angina at baseline had no impact on all-cause mortality (HR, 1.02; 95%CI, 0.71-1.48; P=.898) and cardiovascular mortality (HR, 1.2; 95%CI, 0.69-2.11; P=.517) at 1 year. However, persistent angina at 30 days post-TAVR was associated with increased all-cause mortality (HR, 4.86; 95%CI, 1.71-13.8; P=.003) and cardiovascular mortality (HR, 20.7; 95%CI, 3.50-122.6; P=.001) at 1-year follow-up. CONCLUSIONS: More than one-fourth of patients with severe aortic stenosis undergoing TAVR had angina prior to the procedure. Angina at baseline did not appear to be a sign of a more advanced valvular disease and had no prognostic impact; however, persistent angina at 30 days post-TAVR was associated with worse clinical outcomes.

Site-Specific Introduction of Alanines for the Nuclear Magnetic Resonance Investigation of Low-Complexity Regions and Large Biomolecular Assemblies.

Nuclear magnetic resonance (NMR) studies of large biomolecular machines and highly repetitive proteins remain challenging due to the difficulty of assigning frequencies to individual nuclei. Here, we present an efficient strategy to address this challenge by engineering a Pyrococcus horikoshii tRNA/alanyl-tRNA synthetase pair that enables the incorporation of up to three isotopically labeled alanine residues in a site-specific manner using in vitro protein expression. The general applicability of this approach for NMR assignment has been demonstrated by introducing isotopically labeled alanines into four distinct proteins: huntingtin exon-1, HMA8 ATPase, the 300 kDa molecular chaperone ClpP, and the alanine-rich Phox2B transcription factor. For large protein assemblies, our labeling approach enabled unambiguous assignments while avoiding potential artifacts induced by site-specific mutations. When applied to Phox2B, which contains two poly-alanine tracts of nine and twenty alanines, we observed that the helical stability is strongly dependent on the homorepeat length. The capacity to selectively introduce alanines with distinct labeling patterns is a powerful tool to probe structure and dynamics of challenging biomolecular systems.

Magnetic resonance imaging reference values for cardiac morphology, function and tissue composition in adolescents.

Background: Cardiovascular magnetic resonance (CMR) is a precise tool for the assessment of cardiac anatomy, function, and tissue composition. However, studies providing CMR reference values in adolescence are scarce. We aim to provide sex-specific CMR reference values for biventricular and atrial dimensions and function and myocardial relaxation times in this population. Methods: Adolescents aged 15-18 years with no known cardiovascular disease underwent a non-contrast 3-T CMR scan between March 2021 and October 2021. The imaging protocol included a cine steady-state free-precession sequence for the analysis of chamber size and function, as well as T2-GraSE and native MOLLI T1-mapping for the characterization of myocardial tissue. Findings: CMR scans were performed in 123 adolescents (mean age 16 ± 0.5 years, 52% girls). Mean left and right ventricular end-diastolic indexed volumes were higher in boys than in girls (91.7 ± 11.6 vs 78.1 ± 8.3 ml/m2, p < 0.001; and 101.3 ± 14.1 vs 84.1 ± 10.5 ml/m2, p < 0.001), as was the indexed left ventricular mass (48.5 ± 9.6 vs 36.6 ± 6.0 g/m2, p < 0.001). Left ventricular ejection fraction showed no significant difference by sex (62.2 ± 4.1 vs 62.8 ± 4.2%, p = 0.412), whereas right ventricular ejection fraction trended slightly lower in boys (55.4 ± 4.7 vs. 56.8 ± 4.4%, p = 0.085). Indexed atrial size and function parameters did not differ significantly between sexes. Global myocardial native T1 relaxation time was lower in boys than in girls (1215 ± 23 vs 1252 ± 28 ms, p < 0.001), whereas global myocardial T2 relaxation time did not differ by sex (44.4 ± 2.0 vs 44.1 ± 2.4 ms, p = 0.384). Sex-stratified comprehensive percentile tables are provided for most relevant cardiac parameters. Interpretation: This cross-sectional study provides overall and sex-stratified CMR reference values for cardiac dimensions and function, and myocardial tissue properties, in adolescents. This information is useful for clinical practice and may help in the differential diagnosis of cardiac diseases, such as cardiomyopathies and myocarditis, in this population. Funding: Instituto de Salud Carlos III (PI19/01704).

Multi-site-specific isotopic labeling accelerates high-resolution structural investigations of pathogenic huntingtin exon-1.

Huntington's disease neurodegeneration occurs when the number of consecutive glutamines in the huntingtin exon-1 (HTTExon1) exceeds a pathological threshold of 35. The sequence homogeneity of HTTExon1 reduces the signal dispersion in NMR spectra, hampering its structural characterization. By simultaneously introducing three isotopically labeled glutamines in a site-specific manner in multiple concatenated samples, 18 glutamines of a pathogenic HTTExon1 with 36 glutamines were unambiguously assigned. Chemical shift analyses indicate the α-helical persistence in the homorepeat and the absence of an emerging toxic conformation around the pathological threshold. Using the same type of samples, the recognition mechanism of Hsc70 molecular chaperone has been investigated, indicating that it binds to the N17 region of HTTExon1, inducing the partial unfolding of the poly-Q. The proposed strategy facilitates high-resolution structural and functional studies in low-complexity regions.

The structure of pathogenic huntingtin exon 1 defines the bases of its aggregation propensity.

Huntington's disease is a neurodegenerative disorder caused by a CAG expansion in the first exon of the HTT gene, resulting in an extended polyglutamine (poly-Q) tract in huntingtin (httex1). The structural changes occurring to the poly-Q when increasing its length remain poorly understood due to its intrinsic flexibility and the strong compositional bias. The systematic application of site-specific isotopic labeling has enabled residue-specific NMR investigations of the poly-Q tract of pathogenic httex1 variants with 46 and 66 consecutive glutamines. Integrative data analysis reveals that the poly-Q tract adopts long α-helical conformations propagated and stabilized by glutamine side chain to backbone hydrogen bonds. We show that α-helical stability is a stronger signature in defining aggregation kinetics and the structure of the resulting fibrils than the number of glutamines. Our observations provide a structural perspective of the pathogenicity of expanded httex1 and pave the way to a deeper understanding of poly-Q-related diseases.

A cyclin-dependent kinase-mediated phosphorylation switch of disordered protein condensation.

Cell cycle transitions result from global changes in protein phosphorylation states triggered by cyclin-dependent kinases (CDKs). To understand how this complexity produces an ordered and rapid cellular reorganisation, we generated a high-resolution map of changing phosphosites throughout unperturbed early cell cycles in single Xenopus embryos, derived the emergent principles through systems biology analysis, and tested them by biophysical modelling and biochemical experiments. We found that most dynamic phosphosites share two key characteristics: they occur on highly disordered proteins that localise to membraneless organelles, and are CDK targets. Furthermore, CDK-mediated multisite phosphorylation can switch homotypic interactions of such proteins between favourable and inhibitory modes for biomolecular condensate formation. These results provide insight into the molecular mechanisms and kinetics of mitotic cellular reorganisation.