Long-Term Plate Complications in Patient-Specific Plates Utilizing Computer-Aided Design.

OBJECTIVE: Assess the long-term plate complications with patient-specific plates (PSPs) created with computer-aided design (CAD) and computer-aided manufacturing (CAM) for fibula free flap reconstructions for mandibular defects. METHODS: Retrospective chart review from January 2010 to July 2022 of patients who underwent mandibular reconstruction with a fibula free flap and PSP. Primary outcome was plating-related complications, defined as plate exposure, fracture, loose screws, and plate removal. RESULTS: A total of 221 patients underwent PSP fibula reconstruction. Average age was 59.8 + 14.3 years old with male to female ratio of 2:1. Squamous cell carcinoma of the mandible was the most common reason for resection, 47.5%, n = 105. Plate removal occurred in 11% of patients (n = 25) about 17.4 months after the initial surgery. Plates were removed due to exposure (76%, n = 19) or screw loosening (24%, n = 6). Malignancy was associated with an increased risk of plate complications when compared to benign tumor (odds ratio [OR] 9.04, confidence interval [CI] 1.36-3.85), osteonecrosis (OR 1.38, CI 0.59-3.48), and trauma (OR 1.26, CI 0.23-12.8). Postoperative radiation therapy (OR 2.27, CI 1.07-4.82, p = 0.026) and surgical site infection (OR 9.22, CI 4.11-21.88, p = 0.001) were associated with more plate complications. CONCLUSIONS: CAD creates PSPs that remain stable in the majority of patients over the long term. Plate removal is less compared to non-PSP reconstruction. Consideration of the soft tissue envelope over the plate and management of perioperative infection at the time of surgery should be entertained. LEVEL OF EVIDENCE: Level 4 Laryngoscope, 2024.

Myosin-5 varies its step length to carry cargo straight along the irregular F-actin track.

Molecular motors employ chemical energy to generate unidirectional mechanical output against a track while navigating a chaotic cellular environment, potential disorder on the track, and against Brownian motion. Nevertheless, decades of nanometer-precise optical studies suggest that myosin-5a, one of the prototypical molecular motors, takes uniform steps spanning 13 subunits (36 nm) along its F-actin track. Here, we use high-resolution interferometric scattering microscopy to reveal that myosin takes strides spanning 22 to 34 actin subunits, despite walking straight along the helical actin filament. We show that cumulative angular disorder in F-actin accounts for the observed proportion of each stride length, akin to crossing a river on variably spaced stepping stones. Electron microscopy revealed the structure of the stepping molecule. Our results indicate that both motor and track are soft materials that can adapt to function in complex cellular conditions.

Design and In Silico Evaluation of an Exercise Decision Support System Using Digital Twin Models.

BACKGROUND: Managing glucose levels during exercise is challenging for individuals with type 1 diabetes (T1D) since multiple factors including activity type, duration, intensity and other factors must be considered. Current decision support tools lack personalized recommendations and fail to distinguish between aerobic and resistance exercise. We propose an exercise-aware decision support system (exDSS) that uses digital twins to deliver personalized recommendations to help people with T1D maintain safe glucose levels (70-180 mg/dL) and avoid low glucose (<70 mg/dL) during and after exercise. METHODS: We evaluated exDSS using various exercise and meal scenarios recorded from a large, free-living study of aerobic and resistance exercise. The model inputs were heart rate, insulin, and meal data. Glucose responses were simulated during and after 30-minute exercise sessions (676 aerobic, 631 resistance) from 247 participants. Glucose outcomes were compared when participants followed exDSS recommendations, clinical guidelines, or did not modify behavior (no intervention). RESULTS: exDSS significantly improved mean time in range for aerobic (80.2% to 92.3%, P < .0001) and resistance (72.3% to 87.3%, P < .0001) exercises compared with no intervention, and versus clinical guidelines (aerobic: 82.2%, P < .0001; resistance: 80.3%, P < .0001). exDSS reduced time spent in low glucose for both exercise types compared with no intervention (aerobic: 15.1% to 5.1%, P < .0001; resistance: 18.2% to 6.6%, P < .0001) and was comparable with following clinical guidelines (aerobic: 4.5%, resistance: 8.1%, P = N.S.). CONCLUSIONS: The exDSS tool significantly improved glucose outcomes during and after exercise versus following clinical guidelines and no intervention providing motivation for clinical evaluation of the exDSS system.

Outcomes Following Treatment for Carotid Blowout in Head and Neck Cancer Patients.

OBJECTIVE: The aim of the study was to determine outcomes after interventional radiology treatment of carotid blowout. METHODS: Patients with head and neck cancer and who received interventional radiology treatment for carotid blowout between 2000 and 2022 were included. Pre-treatment, treatment, and post-treatment variables were evaluated. RESULTS: Fourteen patients met inclusion criteria. Eleven patients (78.6%) had a history of radiation. Twelve (85.7%) blowouts occurred within 6 months of recent intervention. Initial treatment was with stenting (n = 9, 64.3%), coil embolization (n = 4, 28.6%), or both (n = 1, 7.1%). Six patients (42.9%) underwent subsequent carotid bypass. Morbidity following treatment included stroke (n = 1) and rebleeding (n = 4). Six-month survival was 57.1%. Of the patients who survived past six months, 5/8 were treated with carotid bypass and coverage. Four patients died of cancer progression, three of rebleeding, and three of medical complications. CONCLUSION: The majority of carotid blowout occurs within 6 months of surgery or radiation. Many who survive will die of cancer progression or medical illness. Carotid bypass with flap coverage may be a worthwhile treatment for carotid blowout and should be considered as an adjunct to endovascular treatment. LEVEL OF EVIDENCE: 4 Laryngoscope, 134:695-700, 2024.

Integrating metabolic expenditure information from wearable fitness sensors into an AI-augmented automated insulin delivery system: a randomised clinical trial.

BACKGROUND: Exercise can rapidly drop glucose in people with type 1 diabetes. Ubiquitous wearable fitness sensors are not integrated into automated insulin delivery (AID) systems. We hypothesised that an AID can automate insulin adjustments using real-time wearable fitness data to reduce hypoglycaemia during exercise and free-living conditions compared with an AID not automating use of fitness data. METHODS: Our study population comprised of individuals (aged 21-50 years) with type 1 diabetes from from the Harold Schnitzer Diabetes Health Center clinic at Oregon Health and Science University, OR, USA, who were enrolled into a 76 h single-centre, two-arm randomised (4-block randomisation), non-blinded crossover study to use (1) an AID that detects exercise, prompts the user, and shuts off insulin during exercise using an exercise-aware adaptive proportional derivative (exAPD) algorithm or (2) an AID that automates insulin adjustments using fitness data in real-time through an exercise-aware model predictive control (exMPC) algorithm. Both algorithms ran on iPancreas comprising commercial glucose sensors, insulin pumps, and smartwatches. Participants executed 1 week run-in on usual therapy followed by exAPD or exMPC for one 12 h primary in-clinic session involving meals, exercise, and activities of daily living, and 2 free-living out-patient days. Primary outcome was time below range (<3·9 mmol/L) during the primary in-clinic session. Secondary outcome measures included mean glucose and time in range (3·9-10 mmol/L). This trial is registered with ClinicalTrials.gov, NCT04771403. FINDINGS: Between April 13, 2021, and Oct 3, 2022, 27 participants (18 females) were enrolled into the study. There was no significant difference between exMPC (n=24) versus exAPD (n=22) in time below range (mean [SD] 1·3% [2·9] vs 2·5% [7·0]) or time in range (63·2% [23·9] vs 59·4% [23·1]) during the primary in-clinic session. In the 2 h period after start of in-clinic exercise, exMPC had significantly lower mean glucose (7·3 [1·6] vs 8·0 [1·7] mmol/L, p=0·023) and comparable time below range (1·4% [4·2] vs 4·9% [14·4]). Across the 76 h study, both algorithms achieved clinical time in range targets (71·2% [16] and 75·5% [11]) and time below range (1·0% [1·2] and 1·3% [2·2]), significantly lower than run-in period (2·4% [2·4], p=0·0004 vs exMPC; p=0·012 vs exAPD). No adverse events occurred. INTERPRETATION: AIDs can integrate exercise data from smartwatches to inform insulin dosing and limit hypoglycaemia while improving glucose outcomes. Future AID systems that integrate exercise metrics from wearable fitness sensors may help people living with type 1 diabetes exercise safely by limiting hypoglycaemia. FUNDING: JDRF Foundation and the Leona M and Harry B Helmsley Charitable Trust, National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases.

Myosin-5 varies its steps along the irregular F-actin track.

Molecular motors employ chemical energy to generate unidirectional mechanical output against a track. By contrast to the majority of macroscopic machines, they need to navigate a chaotic cellular environment, potential disorder in the track and Brownian motion. Nevertheless, decades of nanometer-precise optical studies suggest that myosin-5a, one of the prototypical molecular motors, takes uniform steps spanning 13 subunits (36 nm) along its F-actin track. Here, we use high-resolution interferometric scattering (iSCAT) microscopy to reveal that myosin takes strides spanning 22 to 34 actin subunits, despite walking straight along the helical actin filament. We show that cumulative angular disorder in F-actin accounts for the observed proportion of each stride length, akin to crossing a river on variably-spaced stepping stones. Electron microscopy revealed the structure of the stepping molecule. Our results indicate that both motor and track are soft materials that can adapt to function in complex cellular conditions.

Quantifying insulin-mediated and noninsulin-mediated changes in glucose dynamics during resistance exercise in type 1 diabetes.

Exercise can cause dangerous fluctuations in blood glucose in people living with type 1 diabetes (T1D). Aerobic exercise, for example, can cause acute hypoglycemia secondary to increased insulin-mediated and noninsulin-mediated glucose utilization. Less is known about how resistance exercise (RE) impacts glucose dynamics. Twenty-five people with T1D underwent three sessions of either moderate or high-intensity RE at three insulin infusion rates during a glucose tracer clamp. We calculated time-varying rates of endogenous glucose production (EGP) and glucose disposal (Rd) across all sessions and used linear regression and extrapolation to estimate insulin- and noninsulin-mediated components of glucose utilization. Blood glucose did not change on average during exercise. The area under the curve (AUC) for EGP increased by 1.04 mM during RE (95% CI: 0.65-1.43, P < 0.001) and decreased proportionally to insulin infusion rate (0.003 mM per percent above basal rate, 95% CI: 0.001-0.006, P = 0.003). The AUC for Rd rose by 1.26 mM during RE (95% CI: 0.41-2.10, P = 0.004) and increased proportionally with insulin infusion rate (0.04 mM per percent above basal rate, CI: 0.03-0.04, P < 0.001). No differences were observed between the moderate and high resistance groups. Noninsulin-mediated glucose utilization rose significantly during exercise before returning to baseline roughly 30-min postexercise. Insulin-mediated glucose utilization remained unchanged during exercise sessions. Circulating catecholamines and lactate rose during exercise despite relatively small changes observed in Rd. Results provide an explanation of why RE may pose a lower overall risk for hypoglycemia.NEW & NOTEWORTHY Aerobic exercise is known to cause decreases in blood glucose secondary to increased glucose utilization in people living with type 1 diabetes (T1D). However, less is known about how resistance-type exercise impacts glucose dynamics. Twenty-five participants with T1D performed in-clinic weight-bearing exercises under a glucose clamp. Mathematical modeling of infused glucose tracer allowed for quantification of the rate of hepatic glucose production as well as rates of insulin-mediated and noninsulin-mediated glucose uptake experienced during resistance exercise.

Outcomes of Cranioplasty Reconstructions: Review of Cranioplasty Implants and Free Flap Coverage Variables that Affect Implant Exposure.

BACKGROUND: Complex scalp wounds with cranial/dural involvement are challenging to reconstruct. Successful reconstruction can be achieved with cranial implants/hardware and free flap coverage. Wounds can breakdown and require revision procedures. We addressed reconstructive outcomes of different implants requiring free flaps. OBJECTIVE: To determine the factors associated with implant exposure. DESIGN: Multi-institutional retrospective review of 82 patients, 2000-2020, repaired with cranial implants and free flap coverage. RESULTS: Implant exposure occurred in 13/82 (16%) reconstructions. Flap atrophy or thinning leading to implant exposure occurred in 11/82 (13%) reconstructions, including partial flap atrophy OR 0.05 (95% CI 0.0-0.35) and total flap atrophy OR 0.34 (95% CI 0.02-19.66). Revision surgeries that occurred subsequent to flap reconstruction were also associated with implant exposure (OR 0.02 (95% CI 0.0-0.19)). Implant exposure was not associated with radiation therapy, patient health history, implant type, flap type, or postoperative complications. CONCLUSIONS: Implant exposure is associated with free flap atrophy, leading to inadequate implant coverage and the need for revision surgeries. Completing reconstruction with adequate soft tissue bulk and coverage and avoiding revision surgery may decrease the risk for implant exposure over time. LEVEL OF EVIDENCE: 4 Laryngoscope, 133:2954-2958, 2023.

Assessment of a Decision Support System for Adults with Type 1 Diabetes on Multiple Daily Insulin Injections.

Introduction: DailyDose is a decision support system designed to provide real-time dosing advice and weekly insulin dose adjustments for adults living with type 1 diabetes using multiple daily insulin injections. Materials and Methods: Twenty-five adults were enrolled in this single-arm study. All participants used Dexcom G6 for continuous glucose monitoring, InPen for short-acting insulin doses, and Clipsulin to track long-acting insulin doses. Participants used DailyDose on an iPhone for 8 weeks. The primary endpoint was % time in range (TIR) comparing the 2-week baseline to the final 2-week period of DailyDose use. Results: There were no significant differences between TIR or other glycemic metrics between the baseline period compared to final 2-week period of DailyDose use. TIR significantly improved by 6.3% when more than half of recommendations were accepted and followed compared with 50% or fewer recommendations (95% CI 2.5%-10.1%, P = 0.001). Conclusions: Use of DailyDose did not improve glycemic outcomes compared to the baseline period. In a post hoc analysis, accepting and following recommendations from DailyDose was associated with improved TIR. Clinical Trial Registration Number: NCT04428645.

Success and Outcomes Following a Second Salvage Attempt for Free Flap Compromise in Patients Undergoing Head and Neck Reconstruction.

Importance: Incidence of perioperative free flap compromise is low, with successful salvage in up to 70%. When the flap is compromised a second time, the value of intervening is unknown. Objective: To assess the outcomes of a second revascularization attempt for compromised free flaps. Design, Setting, and Participants: This multicenter retrospective medical record review included patients undergoing head and neck reconstruction with free flaps at 6 US medical centers from January 1, 2000, through December 30, 2020. Patients were 18 years or older with a history of head and neck defects from cancer, osteoradionecrosis, or other wounds. Of 3510 flaps identified, 79 were successfully salvaged once, became compromised a second time, and underwent attempted salvage. Main Outcome and Measure: Flaps with a history of initial compromise and successful revascularization demonstrating second episodes of compromise followed by second salvage attempts. Results: A total of 79 patients (mean age, 64 years; 61 [77%] men) were included in the analysis. Of the 79 flaps undergoing second salvage attempts, 24 (30%) survived while 55 (70%) demonstrated necrosis. Arterial or venous thrombectomy was performed in 17 of the 24 (71%) flaps that survived and 23 of the 55 (42%) flaps demonstrating necrosis (odds ratio, 3.38; 95% CI, 1.21-9.47). When venous compromise was encountered, changing the anastomotic vein was associated with decreased survival compared with not changing the vein (29 of 55 [53%] flaps vs 10 of 24 [42%] flaps); vein revision to an alternative branch was completed in 1 of the 24 (4%) flaps that survived and 19 of the 55 (35%) flaps with necrosis (odds ratio, 0.08; 95% CI, 0.00-0.60). Factors that were not associated with flap survival following second salvage attempts included flap type, cause of flap failure, postoperative complications, patient comorbidities, and heparin administration after second salvage. Conclusions and Relevance: In this cohort study, second salvage was successful in 30% of free flaps. Flaps that underwent arterial or venous thrombectomy demonstrated better survival, while vein revision to neighboring branch veins was associated with worse flap outcomes.

Quantifying the impact of physical activity on future glucose trends using machine learning.

Prevention of hypoglycemia (glucose <70 mg/dL) during aerobic exercise is a major challenge in type 1 diabetes. Providing predictions of glycemic changes during and following exercise can help people with type 1 diabetes avoid hypoglycemia. A unique dataset representing 320 days and 50,000 + time points of glycemic measurements was collected in adults with type 1 diabetes who participated in a 4-arm crossover study evaluating insulin-pump therapies, whereby each participant performed eight identically designed in-clinic exercise studies. We demonstrate that even under highly controlled conditions, there is considerable intra-participant and inter-participant variability in glucose outcomes during and following exercise. Participants with higher aerobic fitness exhibited significantly lower minimum glucose and steeper glucose declines during exercise. Adaptive, personalized machine learning (ML) algorithms were designed to predict exercise-related glucose changes. These algorithms achieved high accuracy in predicting the minimum glucose and hypoglycemia during and following exercise sessions, for all fitness levels.

Assembly principles of the human R2TP chaperone complex reveal the presence of R2T and R2P complexes.

R2TP is a highly conserved chaperone complex formed by two AAA+ ATPases, RUVBL1 and RUVBL2, that associate with PIH1D1 and RPAP3 proteins. R2TP acts in promoting macromolecular complex formation. Here, we establish the principles of R2TP assembly. Three distinct RUVBL1/2-based complexes are identified: R2TP, RUVBL1/2-RPAP3 (R2T), and RUVBL1/2-PIH1D1 (R2P). Interestingly, we find that PIH1D1 does not bind to RUVBL1/RUVBL2 in R2TP and does not function as a nucleotide exchange factor; instead, RPAP3 is found to be the central subunit coordinating R2TP architecture and linking PIH1D1 and RUVBL1/2. We also report that RPAP3 contains an intrinsically disordered N-terminal domain mediating interactions with substrates whose sequences are primarily enriched for Armadillo repeat domains and other helical-type domains. Our work provides a clear and consistent model of R2TP complex structure and gives important insights into how a chaperone machine concerned with assembly of folded proteins into multisubunit complexes might work.

Micromirror Total Internal Reflection Microscopy for High-Performance Single Particle Tracking at Interfaces.

Single particle tracking has found broad applications in the life and physical sciences, enabling the observation and characterization of nano- and microscopic motion. Fluorescence-based approaches are ideally suited for high-background environments, such as tracking lipids or proteins in or on cells, due to superior background rejection. Scattering-based detection is preferable when localization precision and imaging speed are paramount due to the in principle infinite photon budget. Here, we show that micromirror-based total internal reflection dark field microscopy enables background suppression previously only reported for interferometric scattering microscopy, resulting in nanometer localization precision at 6 µs exposure time for 20 nm gold nanoparticles with a 25 × 25 µm2 field of view. We demonstrate the capabilities of our implementation by characterizing sub-nanometer deterministic flows of 20 nm gold nanoparticles at liquid-liquid interfaces. Our results approach the optimal combination of background suppression, localization precision, and temporal resolution achievable with pure scattering-based imaging and tracking of nanoparticles at interfaces.

Mass photometry enables label-free tracking and mass measurement of single proteins on lipid bilayers.

The quantification of membrane-associated biomolecular interactions is crucial to our understanding of various cellular processes. State-of-the-art single-molecule approaches rely largely on the addition of fluorescent labels, which complicates the quantification of the involved stoichiometries and dynamics because of low temporal resolution and the inherent limitations associated with labeling efficiency, photoblinking and photobleaching. Here, we demonstrate dynamic mass photometry, a method for label-free imaging, tracking and mass measurement of individual membrane-associated proteins diffusing on supported lipid bilayers. Application of this method to the membrane remodeling GTPase, dynamin-1, reveals heterogeneous mixtures of dimer-based oligomers, oligomer-dependent mobilities, membrane affinities and (dis)association of individual complexes. These capabilities, together with assay-based advances for studying integral membrane proteins, will enable the elucidation of biomolecular mechanisms in and on lipid bilayers.

Endocast and Bony Labyrinth of a Devonian "Placoderm" Challenges Stem Gnathostome Phylogeny.

Our understanding of the earliest evolution of jawed vertebrates depends on a credible phylogenetic framework for the jawed stem gnathostomes collectively known as "placoderms".1 However, their relationships, and whether placoderms represent a single radiation or a paraphyletic array, remain contentious.2-13 This uncertainty is compounded by an uneven understanding of anatomy across the group, particularly of the phylogenetically informative braincase and brain cavity-endocast. Based on new tomographic data, we here describe the endocast and bony labyrinth of Brindabellaspis stensioi from the Early Devonian of New South Wales.14 The taxon was commonly recovered as branching near the base of placoderms.5-9,11,12,15-17 Previous studies of Brindabellaspis emphasized its resemblances with fossil jawless fishes in the braincase anatomy14 and endocast proportions1,18 and its distinctive features were interpreted as autapomorphies, such as the elongated premedian region.19 Although our three-dimensional data confirmed the resemblance of its endocast to those of jawless vertebrates, we discovered that the inner ear and endolymphatic complex display a repertoire of previously unrecognized characters close to modern or crown-group jawed vertebrates, including a pronounced sinus superior and a vertical duct that connects the endolymphatic sac and the labyrinth cavity. Both parsimony and Bayesian analyses suggest that prevailing hypotheses of placoderm relationships are unstable, with newly revealed anatomy pointing to a radical revision of early gnathostome evolution. Our results call into question the appropriateness of arthrodire-like placoderms as models of primitive gnathostome anatomy and raise questions of homology relating to key cranial features.

Management of the Acute Loss of a Free Flap to the Head and Neck-A Multi-institutional Review.

OBJECTIVES/HYPOTHESIS: To review the management of failed free tissue transfers among four large institutions over a 13-year period to provide data and analysis for a logical, algorithmic, experience-based approach to the management of failed free flaps. STUDY DESIGN: Retrospective case series. METHODS: A multi-institutional retrospective chart review of free tissue transfers to the head and neck region between 2006 and 2019 was performed. Patients with a failed free flap during their hospitalization after surgery to the head and neck were identified and reviewed. Patient age, co-morbidities, risk factors, flap characteristics, tumor specifics, and length of hospital stay were reviewed, collected, and analyzed. RESULTS: One hundred eighteen flap failures met criteria. The most common failed flap in this review was the osteocutaneous flap 52/118 (44%). The recipient site of the initial free flap (P < .001) was the only statistically significant parameter strongly correlated with management. Osteocutaneous flap failures, fasciocutaneous, bowel, and muscle-only flaps tended to be managed most commonly with a second free flap. Myocutaneous flap failures were managed equally with either a second free flap or a regional flap. CONCLUSIONS: The most important factor in management of a failed free flap is the recipient site. A second free flap is often the preferred treatment, but in the acute setting, local or regional flaps may be viable options depending on the recipient site, circumstances of flap loss, and patient- specific comorbidities. An algorithm for management of the acute flap loss is presented in this review. LEVEL OF EVIDENCE: 4 Laryngoscope, 131:518-524, 2021.

Application of the Spider Limb Positioner to Subscapular System Free Flaps.

OBJECTIVE: To demonstrate the application and surgical time savings of the Spider Limb Positioner for subscapular system free flaps in head and neck reconstructive surgery. METHODS: Single institution retrospective chart review and analysis of patients between 2011 and 2019 that underwent a subscapular system free flap either with or without use of the Spider Limb Positioner. One hundred five patients in total were reviewed with 53 patients in the Spider group. The surgical times were compared between the two groups. Patient-specific information regarding average age, laterality of donor site, recipient site, gender, and flap type were reviewed. RESULTS: Forty-one patients in both groups underwent a latissimus free flap. Twelve of 53 in the Spider group and 11/52 in the control group underwent a scapula free flap. The average age in the Spider group at the time of surgery was 64 years. The recipient sites for the Spider groups were reviewed. The free flap was ipsilateral to the defect in 81% of cases. The mean surgical time for the 105 patients without the Spider was 568 minutes versus 486 minutes with a Spider P-value of .003478. CONCLUSION: Use of the Spider Limb Positioner allows for a simultaneous two-team approach during free flap elevation of the subscapular system, which eliminates both dependence on an assistant to support the arm and time consuming positioning changes during flap elevation. LEVEL OF EVIDENCE: 3 Laryngoscope, 131:525-528, 2021.

Quantifying the heterogeneity of macromolecular machines by mass photometry.

Sample purity is central to in vitro studies of protein function and regulation, and to the efficiency and success of structural studies using techniques such as x-ray crystallography and cryo-electron microscopy (cryo-EM). Here, we show that mass photometry (MP) can accurately characterize the heterogeneity of a sample using minimal material with high resolution within a matter of minutes. To benchmark our approach, we use negative stain electron microscopy (nsEM), a popular method for EM sample screening. We include typical workflows developed for structure determination that involve multi-step purification of a multi-subunit ubiquitin ligase and chemical cross-linking steps. When assessing the integrity and stability of large molecular complexes such as the proteasome, we detect and quantify assemblies invisible to nsEM. Our results illustrate the unique advantages of MP over current methods for rapid sample characterization, prioritization and workflow optimization.

Myosin II Filament Dynamics in Actin Networks Revealed with Interferometric Scattering Microscopy.

The plasma membrane and the underlying cytoskeletal cortex constitute active platforms for a variety of cellular processes. Recent work has shown that the remodeling acto-myosin network modifies local membrane organization, but the molecular details are only partly understood because of difficulties with experimentally accessing the relevant time and length scales. Here, we use interferometric scattering microscopy to investigate a minimal acto-myosin network linked to a supported lipid bilayer membrane. Using the magnitude of the interferometric contrast, which is proportional to molecular mass, and fast acquisition rates, we detect and image individual membrane-attached actin filaments diffusing within the acto-myosin network and follow individual myosin II filament dynamics. We quantify myosin II filament dwell times and processivity as functions of ATP concentration, providing experimental evidence for the predicted ensemble behavior of myosin head domains. Our results show how decreasing ATP concentrations lead to both increasing dwell times of individual myosin II filaments and a global change from a remodeling to a contractile state of the acto-myosin network.

Interferometric Scattering Microscopy.

Interferometric scattering microscopy (iSCAT) is an extremely sensitive imaging method based on the efficient detection of light scattered by nanoscopic objects. The ability to, at least in principle, maintain high imaging contrast independent of the exposure time or the scattering cross section of the object allows for unique applications in single-particle tracking, label-free imaging of nanoscopic (dis)assembly, and quantitative single-molecule characterization. We illustrate these capabilities in areas as diverse as mechanistic studies of motor protein function, viral capsid assembly, and single-molecule mass measurement in solution. We anticipate that iSCAT will become a widely used approach to unravel previously hidden details of biomolecular dynamics and interactions.