Myosin-Catalyzed ATP Hydrolysis in the Presence of Disease-Causing Mutations: Mavacamten as a Way to Repair Mechanism.

Hypertrophic cardiomyopathy is one of the most common forms of genetic cardiomyopathy. Mavacamten is a first-in-class myosin modulator that was identified via activity screening on the wild type, and it is FDA-approved for the treatment of obstructive hypertrophic cardiomyopathy (HCM). The drug selectively binds to the cardiac ß-myosin, inhibiting myosin function to decrease cardiac contractility. Though the drug is thought to affect multiple steps of the myosin cross-bridge cycle, its detailed mechanism of action is still under investigation. Individual steps in the overall cross-bridge cycle must be queried to elucidate the full mechanism of action. In this study, we utilize the rare-event method of transition path sampling to generate reactive trajectories to gain insights into the action of the drug on the dynamics and rate of the ATP hydrolysis step for human cardiac ß-myosin. We study three known HCM causative myosin mutations: R453C, P710R, and R712L to observe the effect of the drug on the alterations caused by these mutations in the chemical step. Since the crystal structure of the drug-bound myosin was not available at the time of this work, we created a model of the drug-bound system utilizing a molecular docking approach. We find a significant effect of the drug in one case, where the actual mechanism of the reaction is altered from the wild type by mutation. The drug restores both the rate of hydrolysis to the wildtype level and the mechanism of the reaction. This is a way to check the effect of the drug on untested mutations.

Reintervention Before Bidirectional Cavopulmonary Shunt and Intermediate Outcomes in Children with Single Ventricle Who Underwent Main Pulmonary Artery Banding.

Unplanned reinterventions following pulmonary artery banding (PAB) in single ventricle patients are common before stage 2 palliation (S2P) but associated risk factors are unknown. We hypothesized that reintervention is more common when PAB is placed at younger age and with a looser band, reflected by lower PAB pressure gradient. Retrospective single center study of single ventricle patients undergoing PAB between Jan 2000 and Dec 2020. The association with reintervention and successful S2P was modeled using exploratory cause-specific hazard regression. A multivariable model was developed adjusting for clinical and statistically relevant predictors. The cumulative proportion of patients undergoing reintervention were summarized using a competing risk model. 77 patients underwent PAB at median (IQR) 47 (24-66) days and 3.73 (3.2-4.5) kg. Within18 months of PAB, 60 (78%) reached S2P, 9 (12%) died, 1 (1%) transplanted and 7 (9%) were alive without S2P. Within 18 months of PAB 10 (13%) patients underwent reintervention related to pulmonary blood flow modification: PAB adjustment (n = 6) and conversion to Damus-Kaye-Stansel/Blalock-Taussig-Thomas shunt (n = 4). 6/10 (60%) reached S2P following reintervention. A trend toward higher intervention in patients with a genetic syndrome (p-0.06) and weight < 3 kg (p-0.057) at time of PAB was noted. Only genetic syndrome was a risk factor associated with poor outcome (p-0.025). PAB has a reasonable outcome in SV patients with unobstructed systemic and pulmonary blood flow, but with a high reintervention rate. Only a quarter of patients with genetic syndromes reach S2P and further study is required to explore the benefits from an alternative palliative strategy.

Frosted Branch Angiitis in the Setting of Active COVID-19 Infection and Underlying Mixed Connective Tissue Disease.

Frosted branch angiitis (FBA) is an uncommon form of retinal vasculitis and is typically associated with vision loss. We report a unique case of FBA that manifested in the setting of an active COVID-19 infection in a patient with Mixed Connective Tissue Disease (MCTD). A 34-year-old female with a history of MCTD, including overlapping findings of dermatomyositis, systemic lupus erythematosus, and rheumatoid arthritis, on immunosuppressive medications, presented for left-sided vision loss. She was also found to have an active COVID-19 infection with symptoms including sore throat and dry cough. The patient's visual acuity was counting fingers in her affected eye with a fundus exam revealing diffuse retinal hemorrhages, retinal whitening, cystoid macular edema, and perivascular sheathing of tertiary arterioles and venules, characteristic of FBA. Labs showed mildly elevated inflammatory markers. She exhibited no other signs or symptoms concerning systemic rheumatologic flare. There was no evidence of COVID-19 on viral PCR testing of intraocular fluid but given her positive nasopharyngeal PCR, COVID-induced retinal vasculitis with FBA remained high on the differential. The patient's retinal vasculitis later improved with heightened immunosuppressive therapy including high-dose intravenous corticosteroids. Clinicians should be aware of the possibility of COVID-related FBA, particularly in patients with an underlying predisposition to autoimmune inflammation. Our experience with this patient highlights the utility of high-dose systemic immunosuppressive therapy in treating such inflammatory occlusive retinal vasculitis. Further studies are needed to characterize retinal manifestations of COVID-19 in the setting of autoimmune disease.

Development of the Residual Lesion Score for congenital heart surgery: the RAND Delphi methodology.

BACKGROUND AND OBJECTIVE: The Residual Lesion Score is a novel tool for assessing the achievement of surgical objectives in congenital heart surgery based on widely available clinical and echocardiographic characteristics. This article describes the methodology used to develop the Residual Lesion Score from the previously developed Technical Performance Score for five common congenital cardiac procedures using the RAND Delphi methodology. METHODS: A panel of 11 experts from the field of paediatric and congenital cardiology and cardiac surgery, 2 co-chairs, and a consultant were assembled to review and comment on validity and feasibility of measuring the sub-components of intraoperative and discharge Residual Lesion Score for five congenital cardiac procedures. In the first email round, the panel reviewed and commented on the Residual Lesion Score and provided validity and feasibility scores for sub-components of each of the five procedures. In the second in-person round, email comments and scores were reviewed and the Residual Lesion Score revised. The modified Residual Lesion Score was scored independently by each panellist for validity and feasibility and used to develop the "final" Residual Lesion Score. RESULTS: The Residual Lesion Score sub-components with a median validity score of ≥7 and median feasibility score of ≥4 that were scored without disagreement and with low absolute deviation from the median were included in the "final" Residual Lesion Score. CONCLUSION: Using the RAND Delphi methodology, we were able to develop Residual Lesion Score modules for five important congenital cardiac procedures for the Pediatric Heart Network's Residual Lesion Score study.

Insights into the Mechanism of the Cardiac Drug Omecamtiv Mecarbil─A Computational Study.

Omecamtiv mecarbil (OM) is a positive inotrope that is thought to bind directly to an allosteric site of the ß-cardiac myosin. The drug is under investigation for the treatment of systolic heart failure. The drug is classified as a cardiac myosin modulator and has been observed to affect multiple vital steps of the cross-bridge cycle including the recovery stroke and the chemical step. We explored the free-energy surface of the recovery stroke of the human cardiac ß-myosin in the presence of OM to determine its influence on this process. We also investigated the effects of OM on the recovery stroke in the presence of genetic cardiomyopathic mutations R712L, F764L, and P710R using metadynamics. We also utilized the method of transition path sampling to generate an unbiased ensemble of reactive trajectories for the ATP hydrolysis step in the presence of OM that were able to provide insight into the differences observed due to OM in the dynamics and mechanism of the decomposition of ATP to ADP and HPO42-, a central part of the power generation in cardiac muscle. We studied chemistry in the presence of the same three mutations to further elucidate the effect of OM, and its use in the treatment of cardiac disease.

Analyzing Continuous Physiologic Data to Find Hemodynamic Signatures Associated With New Brain Injury After Congenital Heart Surgery.

Continuous data capture technology is becoming more common. Establishing analytic approaches for continuous data could aid in understanding the relationship between physiology and clinical outcomes. OBJECTIVES: Our objective was to design a retrospective analysis for continuous physiologic measurements and their relationship with new brain injury over time after cardiac surgery. DESIGN SETTING AND PARTICIPANTS: Retrospective cohort study in the Cardiac Critical Care Unit at the Hospital for Sick Children in patients after repair of transposition of the great arteries (TGA) or single ventricle (SV) lesions. MAIN OUTCOMES AND MEASURES: Continuously acquired physiologic measurements for up to 72 hours after cardiac surgery were analyzed for association with new brain injury by MRI. Distributions of heart rate (HR), systolic blood pressure (BP), and oxygen saturation (Spo2) for SV and TGA were analyzed graphically and with descriptive statistics over postoperative time for data-driven variable selection. Mixed-effects regression analyses characterized relationships between HR, BP, and Spo2 and new brain injury over time while accounting for variation between patients, measurement heterogeneity, and missingness. RESULTS: Seventy-seven patients (60 TGA; 17 SV) were included. New brain injury was seen in 26 (34%). In SV patients, with and without new brain injury, respectively, in the first 24 hours after cardiac surgery, the median (interquartile range) HR was 172.0 beats/min (bpm) (169.7-176.0 bpm) versus 159.6 bpm (145.0-167.0 bpm); systolic BP 74.8 (67.9-78.5 mm Hg) versus 68.9 mm Hg (61.6-70.9 mm Hg). Higher postoperative HR (parameter estimate, 19.4; 95% CI, 7.8-31; p = 0.003 and BP, 8.6; 1.3-15.8; p = 0.024) were associated with new brain injury in SV patients. The strength of this relationship decreased with time. CONCLUSIONS AND RELEVANCE: Retrospective analysis of continuous physiologic measurements can provide insight into changes in postoperative physiology over time and their relationship with new brain injury. This technique could be applied to assess relationships between physiologic data and many patient interventions or outcomes.

Transition Path Sampling Based Calculations of Free Energies for Enzymatic Reactions: The Case of Human Methionine Adenosyl Transferase and Plasmodium vivax Adenosine Deaminase.

Transition path sampling (TPS) is widely used for the calculations of reaction rates, transition state structures, and reaction coordinates of condensed phase systems. Here we discuss a scheme for the calculation of free energies using the ensemble of TPS reactive trajectories in combination with a window-based sampling technique for enzyme-catalyzed reactions. We calculate the free energy profiles of the reactions catalyzed by the human methionine S-adenosyltransferase (MAT2A) enzyme and the Plasmodium vivax adenosine deaminase (pvADA) enzyme to assess the accuracy of this method. MAT2A catalyzes the formation of S-adenosine-l-methionine following a SN2 mechanism, and using our method, we estimate the free energy barrier for this reaction to be 16 kcal mol-1, which is in excellent agreement with the experimentally measured activation energy of 17.27 kcal mol-1. Furthermore, for the pvADA enzyme-catalyzed reaction we estimate a free energy barrier of 21 kcal mol-1, and the calculated free energy profile is similar to that predicted from experimental observations. Calculating free energies by employing our simple method within TPS provides significant advantages over methods such as umbrella sampling because it is free from any applied external bias, is accurate compared to experimental measurements, and has a reasonable computational cost.

Ocular Toxoplasmosis: No Stranger to the Masquerade Ball.

Purpose: This article illustrates multiple atypical manifestations of ocular toxoplasmosis masquerading as acute retinal necrosis and vitreoretinal lymphoma. Methods: Two case presentations are discussed, and the body of pertinent literature is reviewed and discussed. Results: In these cases, an extensive workup and attention to history lead to the correct diagnosis and management. Conclusions: Aggressive cases of ocular toxoplasmosis may present in a variety of phenotypes that may mimic other vision- and potentially life-threatening conditions, particularly in a milieu of inadequate endogenous and exogenous antimicrobial defenses.

Epiretinal proliferation after rhegmatogenous retinal detachment.

PURPOSE: To determine the characteristics and appearance rate of epiretinal proliferation (ERP) on SD-OCT after surgery for rhegmatogenous retinal detachment (RRD) repair. METHODS: One hundred eight eyes of 108 patients who underwent one or more surgeries for RRD were enrolled. The eyes with other maculopathies that were directly related to RRD were excluded. Image acquisition was performed with SD-OCT (Heidelberg Engineering, Germany). Clinical charts were reviewed to assess clinical and surgical findings. Statistical analyses were performed using XLSTAT (Assinsoft, Paris, France). RESULTS: ERP was found in 9.3% eyes (n = 10). The mean initial visual acuity (logMAR) was 1.34 ± 0.82 in the ERP group compared to 0.49 ± 0.70 in the non-ERP group. PVR was present in 70.0% and chronic macular edema was found in 80.0% of eyes which developed ERP. The mean number of vitreoretinal surgeries in eyes with ERP was 3.3 ± 1.19 and only 1.44 ± 1.02 in eyes without. Silicone oil was used in 60.0% of eyes which developed ERP compared to 13.9% in the non-ERP group. CONCLUSION: ERP is a late-onset postoperative finding in eyes with RRD and can occur in absence of macular holes. Overall, ERP is more frequent in eyes with complicated courses of RRD including multiple operations, PVR, usage of silicone oil, and chronic macular edema.

PIGMENT EPITHELIAL DETACHMENT IN AGE-RELATED MACULAR DEGENERATION: Long-Term Visual Acuity May Improve With Higher Injection Index.

PURPOSE: To define injection index (II) and assess its impact on visual acuity (VA) in pigment epithelial detachment from age-related macular degeneration over 5 years. METHODS: Injection index is defined as the mean anti-vascular endothelial growth factor injections per year from presentation. A retrospective study of 256 eyes in 213 patients was performed. Patients were stratified by II (high: ≥9, low: <9). RESULTS: Baseline characteristics showed no differences across II groups. Mean (range) follow-up, in years, was 5.02 (1.04-12.74) for all patients. Mean logMAR VA (Snellen VA) were 0.60 (20/80) and 0.56 (20/73) at baseline, 0.52 (20/66) and 0.59 (20/78) at Year 1, 0.45 (20/56) and 0.67 (20/94) at Year 2, 0.38 (20/48) and 0.66 (20/91) at Year 3, 0.41 (20/51) and 0.89 (20/155) at Year 4, and 0.35 (20/45) and 0.79 (20/123) at Year 5 for the high and low II groups, respectively. Linear regression analysis showed a gain of 0.5 approxETDRS letters with each additional injection per year. CONCLUSION: Increased II was associated with better mean VA, suggesting that long-term continuous vascular endothelial growth factor suppression may improve VA in eyes thought to carry poor prognoses.

Investigation of the Recovery Stroke and ATP Hydrolysis and Changes Caused Due to the Cardiomyopathic Point Mutations in Human Cardiac ß Myosin.

Human cardiac ß myosin undergoes the cross-bridge cycle as part of the force-generating mechanism of cardiac muscle. The recovery stroke is considered one of the key steps of the kinetic cycle as it is the conformational rearrangement required to position the active site residues for hydrolysis of ATP and interaction with actin. We explored the free-energy surface of the transition and investigated the effect of the genetic cardiomyopathy causing mutations R453C, I457T, and I467T on this step using metadynamics. This work extends previous studies on Dictyostelium myosin II with engineered mutations. Here, like previously, we generated an unbiased thermodynamic ensemble of reactive trajectories for the chemical step using transition path sampling. Our methodologies were able to predict the changes to the dynamics of the recovery stroke as well as predict the pathway of breakdown of ATP to ADP and HPO42- with the stabilization of the metaphosphate intermediate. We also observed clear differences between the Dictyostelium myosin II and human cardiac ß myosin for ATP hydrolysis as well as predict the effect of the mutation I467T on the chemical step.

Impact of Major Residual Lesions on Outcomes After Surgery for Congenital Heart Disease.

BACKGROUND: Many factors affect outcomes after congenital cardiac surgery. OBJECTIVES: The RLS (Residual Lesion Score) study explored the impact of severity of residual lesions on post-operative outcomes across operations of varying complexity. METHODS: In a prospective, multicenter, observational study, 17 sites enrolled 1,149 infants undergoing 5 common operations: tetralogy of Fallot repair (n = 250), complete atrioventricular septal defect repair (n = 249), arterial switch operation (n = 251), coarctation or interrupted arch with ventricular septal defect (VSD) repair (n = 150), and Norwood operation (n = 249). The RLS was assigned based on post-operative echocardiography and clinical events: RLS 1 (trivial or no residual lesions), RLS 2 (minor residual lesions), or RLS 3 (reintervention for or major residual lesions before discharge). The primary outcome was days alive and out of hospital within 30 post-operative days (60 for Norwood). Secondary outcomes assessed post-operative course, including major medical events and days in hospital. RESULTS: RLS 3 (vs. RLS 1) was an independent risk factor for fewer days alive and out of hospital (p ≤ 0.008) and longer post-operative hospital stay (p ≤ 0.02) for all 5 operations, and for all secondary outcomes after coarctation or interrupted arch with VSD repair and Norwood (p ≤ 0.03). Outcomes for RLS 1 versus 2 did not differ consistently. RLS alone explained 5% (tetralogy of Fallot repair) to 20% (Norwood) of variation in the primary outcome. CONCLUSIONS: Adjusting for pre-operative factors, residual lesions after congenital cardiac surgery impacted in-hospital outcomes across operative complexity with greatest impact following complex operations. Minor residual lesions had minimal impact. These findings may provide guidance for surgeons when considering short-term risks and benefits of returning to bypass to repair residual lesions.

Macular edema after rhegmatogenous retinal detachment repair: risk factors, OCT analysis, and treatment responses.

PURPOSE: To investigate risk factors, imaging characteristics, and treatment responses of cystoid macular edema (CME) after rhegmatogenous retinal detachment (RRD) repair. METHODS: Consecutive, retrospective case-control series of patients who underwent pars plana vitrectomy (PPV) and/or scleral buckling (SB) for RRD, with at least six months of follow-up. Clinical and surgical parameters of patients with and without CME (nCME), based on spectral-domain optical coherence tomography (OCT), were compared. RESULTS: Of 99 eyes enrolled, 25 had CME while 74 had nCME. Patients with CME underwent greater numbers of surgeries (P < 0.0001). After adjusting for number of surgeries, macula-off RRD (P = 0.06), proliferative vitreoretinopathy (PVR) (P = 0.09), surgical approach (PPV and/or SB, P = 0.21), and tamponade type (P = 0.10) were not statistically significant, although they all achieved significance on univariate analysis (P = 0.001 or less). Intraoperative retinectomy (P = 0.009) and postoperative pseudophakia or aphakia (P = 0.008) were more frequent in the CME group, even after adjustment. Characteristics of cCME on OCT included diffuse distribution, confluent cysts, and absence of subretinal fluid or intraretinal hyperreflective foci. Macular thickness improved significantly with intravitreal triamcinolone (P = 0.016), but not with anti-vascular endothelial growth factor agents (P = 0.828) or dexamethasone implant (P = 0.125). After adjusting for number of surgeries and macular detachment, final visual acuities remained significantly lower in the CME vs nCME group (P = 0.012). CONCLUSION: Risk factors of CME include complex retinal detachment repairs requiring multiple surgeries, and pseudophakic or aphakic lens status. Although this cCME was associated with poor therapeutic response, corticosteroids were the most effective studied treatments.

Clinical characteristics and visual outcomes of non-resolving subretinal fluid in neovascular AMD despite continuous monthly anti-VEGF injections: a long-term follow-up.

PURPOSE: To describe the clinical characteristics and visual outcomes of neovascular age-related macular degeneration (NV-AMD) patients with irregular pigment epithelium detachment (PED) and non-resolving subretinal fluid (SRF) despite continuous monthly injections of anti-vascular endothelial growth factor (VEGF). METHODS: This is a retrospective case series, including NV-AMD patients treated in a tertiary academic practice. Inclusion criteria were NV-AMD diagnosis, with irregular PED, and non-resolving SRF treated with continuous monthly anti-VEGF intravitreal injections. Data collection included best corrected visual acuity (BCVA), central macular thickness (CMT), sub-foveal choroidal thickness (SFCT), and type and location of PED as seen on optical coherence tomography (OCT). RESULTS: A total of 738 patients with NV-AMD underwent anti-VEGF injections during the follow-up period and 20 eyes of 19 patients (14 females and 5 males) met the inclusion criteria. Average age was 81.7 ± 6.6 years, mean follow-up time was 32.1 ± 23.5 months, and mean number of injections was 31.3 ± 24.2. Mean VA was 0.26 ± 0.21 logMAR (Snellen 20/36) at baseline versus 0.20 ± 0.23 logMAR (Snellen 20/32) at the end of the follow-up (P = 0.28). All eyes presented with sub-foveal, type 1 macular neovascularization (MNV). Average sub-foveal choroidal thickness changed from 189.70 ± 68.46 µm at baseline to 169.00 ± 63.06 µm (P < 0.001) at last follow-up. CONCLUSION: Patients with type 1 NV-AMD, irregular PED, and non-resolving SRF and under continuous treatment of monthly anti-VEGF injections may maintain good visual acuity after long period of time.

Can We Still Improve Survival Outcomes of Neonatal Biventricular Repairs?

BACKGROUND: We sought to identify modifiable factors to improve survival of neonatal biventricular repair by analyzing the cause of death and predictors of mortality and reintervention in the last 2 decades. METHODS: Between 1995 and 2016, 991 consecutive neonates were included. The cohort was divided by era: era I was from 1995 to 1999, era II 2000 to 2007, and era III 2008 to 2016. The Kaplan-Meier method was used to estimate freedom from death and reintervention. Univariable and multivariable Cox regression was applied to assess predictors for mortality or reintervention in the contemporary cohorts (2000-2016). RESULTS: Median age was 8 days (range, 5-13), and median body weight at operation was 3.3 kg (range, 2.9-3.6). The most common diagnosis was transposition with intact ventricular septum (32%), followed by transposition with ventricular septal defect (14.5%), and simple left-to-right shunt lesion (10.9%). There was significant improvement in survival from era I to eras II and III but no difference between eras II and III (1 year: 82.1% vs 89.4% vs 89.6%, respectively; P < .001). The most common cause of death was sudden death in eras I and III and cardiac in era II. Multivariable analysis revealed preoperative (P = .005)/postoperative (P < .001) extracorporeal membrane oxygenation and postoperative renal replacement (P < .001) as independent predictors for mortality. The reintervention rates were comparable between eras II and III (P = .53). Atrioventricular septal defects and common atrial trunk were identified as predictors for reintervention. CONCLUSIONS: Survival after neonatal biventricular repair remained unchanged. Preventing sudden death, myocardial protection, and minimizing residual lesions are potential targets to improve outcomes.

Mastermind: A Comprehensive Genomic Association Search Engine for Empirical Evidence Curation and Genetic Variant Interpretation.

Design and interpretation of genome sequencing assays in clinical diagnostics and research labs is complicated by an inability to identify information from the medical literature and related databases quickly, comprehensively and reproducibly. This challenge is compounded by the complexity and heterogeneity of nomenclatures used to describe diseases, genes and genetic variants. Mastermind is a widely-used bioinformatic platform of genomic associations that has indexed more than 7.5 M full-text articles and 2.5 M supplemental datasets. It has automatically identified, disambiguated and annotated >6.1 M genetic variants and identified >50 K disease-gene associations. Here, we describe how Mastermind improves the sensitivity and reproducibility of clinical variant interpretation and produces comprehensive genomic landscapes of genetic variants driving pharmaceutical research. We demonstrate an alarmingly high degree of heterogeneity across commercially available panels for hereditary cancer that is resolved by evidence from Mastermind. We further examined the sensitivity of Mastermind for variant interpretation by examining 108 clinically-encountered variants and comparing the results to alternate methods. Mastermind demonstrated a sensitivity of 98.4% compared to 4.4, 45.6, and 37.4% for alternatives PubMed, Google Scholar, and ClinVar, respectively, and a specificity of 98.5% compared to 45.1, 57.6, and 68.8% as well as an increase in content yield of 22.6-, 2.2-, and 2.6-fold. When curated for clinical significance, Mastermind identified more than 4.9-fold more pathogenic variants than ClinVar for representative genes. For structural variants, we compared Mastermind's ability to sensitively identify evidence for 10 representative disease-causing CNVs versus results identified in PubMed, as well as its ability to identify evidence for fusion events compared to COSMIC. Mastermind demonstrated a 4.0- to 43.9-fold increase in references for specific CNVs compared to PubMed, as well as 5.4-fold more fusion genes when compared with COSMIC's curated database. Additionally, Mastermind produced an 8.0-fold increase in reference citations for fusion events common to Mastermind and outside databases. Taken together, these results demonstrate the utility and superiority of Mastermind in terms of both sensitivity and specificity of automated results for clinical diagnostic variant interpretation for multiple genetic variant types and highlight the potential benefit in informing pharmaceutical research.

Mechanochemical Function of Myosin II: Investigation into the Recovery Stroke and ATP Hydrolysis.

Myosin regulates muscle function through a complex cycle of conformational rearrangements coupled with the hydrolysis of adenosine triphosphate (ATP). The recovery stroke reorganizes the myosin active site to hydrolyze ATP and cross bridge with the thin filament to produce muscle contraction. Engineered mutations K84M and R704E in Dictyostelium myosin have been designed to specifically inhibit the recovery stroke and have been shown to indirectly affect the ATPase activity of myosin. We investigated these mutagenic perturbations to the recovery stroke and generated thermodynamically correct and unbiased trajectories for native ATP hydrolysis with computationally enhanced sampling methods. Our methodology was able to resolve experimentally observed changes to kinetic and equilibrium dynamics for the recovery stroke with the correct prediction in the severity of these changes. For ATP hydrolysis, the sequential nature along with the stabilization of a metaphosphate intermediate was observed in agreement with previous studies. However, we observed glutamate 459 being utilized as a proton abstractor to prime the attacking water instead of a lytic water, a phenomenon not well categorized in myosin but has in other ATPases. Both rare event methodologies can be extended to human myosin to investigate isoformic differences from Dictyostelium and scan cardiomyopathic mutations to see differential perturbations to kinetics of other conformational changes in myosin such as the power stroke.

Carbon Dots for Efficient Small Interfering RNA Delivery and Gene Silencing in Plants.

The initiation of RNA interference (RNAi) by topically applied small interfering RNA has potential applications for plant functional genomics, crop improvement and crop protection, but the primary obstacle for the development of this technology is the efficient delivery of RNAi effectors into the cell. The plant cell wall is a particularly challenging barrier for the delivery of macromolecules because many of the transfection agents that are commonly used with animal cells produce nanocomplexes that are significantly larger than the size exclusion limit of the cell wall. Here, we illustrate the use of a class of very small nanoparticles, called carbon dots, for delivering small interfering RNA into the model plants Nicotiana benthamiana and tomato (Solanum lycopersicum). Low-pressure spray application of these formulations with a spreading surfactant resulted in strong silencing of GFP transgenes in both species. The delivery efficacy of carbon dot formulations was also demonstrated by the silencing of endogenous genes that encode two subunits of magnesium chelatase, an enzyme necessary for chlorophyll synthesis. The strong visible phenotypes observed with the carbon dot-facilitated delivery were validated by measuring significant reductions in the target gene transcript and/or protein levels. Methods for the delivery of RNAi effectors into plants, such as the carbon dot formulations described here, could become valuable tools for gene silencing in plants with practical applications in plant functional genomics and agriculture.