Thermal damage to the skin from 8.2 and 95 GHz microwave exposures in swine.

A study of burn thresholds from superficially penetrating radio-frequency (RF) energy at 8.2 and 95 GHz for swine skin was conducted. The study determined the thresholds for superficial, partial-thickness, and full-thickness burn severities after 5 seconds of exposure at power densities of 4-30 W/cm2and 2-15 W/cm2at 8.2 and 95 GHz, respectively. There were significant differences in he burn thresholds at the different severities between the two frequencies due to the large difference in energy penetration depths. Biopsies were collected from each burn site at 1, 24, 72, and 168 hr post exposure. Each sample was assessed by a burn pathologist against 20 histological factors to characterize the damage resulting from these RF overexposures. A one-dimensional, layered digital phantom that utilized realistic values for dielectric and thermal properties was used to explain some observed thresholds. The results of the heating and cooling response of the animal model and histology scores of each exposure are provided to enhance future efforts at simulation of RF overexposures and to establish damage thresholds.

Behavioral pathways from sibling relationships in adolescence to romantic partnerships in adulthood.

Sibling relationships in adolescence provide rich and relevant socializing opportunities for developing early adult romantic relationships, but much less is known regarding the effect of siblings on future romantic partnerships. Using a prospective, longitudinal design, we investigated the association between observed positive behaviors (warmth, support, positive communication), sibling pairs during adolescence (7th, 8th, 9th, and 10th grades), and the same observed behaviors between adult romantic partners nearly two decades later (M age = 31 years old). In structural equation models (SEMs), we tested four dyadic pathways of interest: (1) individual behavioral continuity; (2) evocative partner effects; (3) sibling modeling; and (4) sibling-to-partner matching. In multiple group analyses, we also investigated gendered socialization effects for different sibling dyads (i.e., brother-brother; sister-sister; and mixed-sex sibling pairs). Results showed strong continuity from adolescent behavior toward their sibling to the same behavior toward their romantic partner in early adulthood, but there was no evidence for sibling modeling effects nor for sibling matching. We also found significant differences between sister-sister sibling dyads compared to brother-brother and mixed-sex sibling dyads for the evocative pathway. Findings highlight the "long view" of positive adolescent behavior in sibling relationships for shaping future romantic partnerships in adulthood.

Anti-apoptotic MCL-1 promotes long-chain fatty acid oxidation through interaction with ACSL1.

MCL-1 is essential for promoting the survival of many normal cell lineages and confers survival and chemoresistance in cancer. Beyond apoptosis regulation, MCL-1 has been linked to modulating mitochondrial metabolism, but the mechanism(s) by which it does so are unclear. Here, we show in tissues and cells that MCL-1 supports essential steps in long-chain (but not short-chain) fatty acid ß-oxidation (FAO) through its binding to specific long-chain acyl-coenzyme A (CoA) synthetases of the ACSL family. ACSL1 binds to the BH3-binding hydrophobic groove of MCL-1 through a non-conventional BH3-domain. Perturbation of this interaction, via genetic loss of Mcl1, mutagenesis, or use of selective BH3-mimetic MCL-1 inhibitors, represses long-chain FAO in cells and in mouse livers and hearts. Our findings reveal how anti-apoptotic MCL-1 facilitates mitochondrial metabolism and indicate that disruption of this function may be associated with unanticipated cardiac toxicities of MCL-1 inhibitors in clinical trials.

The carboxy terminus causes interfacial assembly of oleate hydratase on a membrane bilayer.

The soluble flavoprotein oleate hydratase (OhyA) hydrates the 9-cis double bond of unsaturated fatty acids. OhyA substrates are embedded in membrane bilayers; OhyA must remove the fatty acid from the bilayer and enclose it in the active site. Here, we show that the positively charged helix-turn-helix motif in the carboxy terminus (CTD) is responsible for interacting with the negatively charged phosphatidylglycerol (PG) bilayer. Super-resolution microscopy of Staphylococcus aureus cells expressing green fluorescent protein fused to OhyA or the CTD sequence shows subcellular localization along the cellular boundary, indicating OhyA is membrane-associated and the CTD sequence is sufficient for membrane recruitment. Using cryo-electron microscopy, we solved the OhyA dimer structure and conducted 3D variability analysis of the reconstructions to assess CTD flexibility. Our surface plasmon resonance experiments corroborated that OhyA binds the PG bilayer with nanomolar affinity and we found the CTD sequence has intrinsic PG binding properties. We determined that the nuclear magnetic resonance structure of a peptide containing the CTD sequence resembles the OhyA crystal structure. We observed intermolecular NOE from PG liposome protons next to the phosphate group to the CTD peptide. The addition of paramagnetic MnCl2 indicated the CTD peptide binds the PG surface but does not insert into the bilayer. Molecular dynamics simulations, supported by site-directed mutagenesis experiments, identify key residues in the helix-turn-helix that drive membrane association. The data show that the OhyA CTD binds the phosphate layer of the PG surface to obtain bilayer-embedded unsaturated fatty acids.

Design of intrinsically disordered protein variants with diverse structural properties.

Intrinsically disordered proteins (IDPs) perform a wide range of functions in biology, suggesting that the ability to design IDPs could help expand the repertoire of proteins with novel functions. Designing IDPs with specific structural or functional properties has, however, been difficult, in part because determining accurate conformational ensembles of IDPs generally requires a combination of computational modelling and experiments. Motivated by recent advancements in efficient physics-based models for simulations of IDPs, we have developed a general algorithm for designing IDPs with specific structural properties. We demonstrate the power of the algorithm by generating variants of naturally occurring IDPs with different levels of compaction and that vary more than 100 fold in their propensity to undergo phase separation, even while keeping a fixed amino acid composition. We experimentally tested designs of variants of the low-complexity domain of hnRNPA1 and find high accuracy in our computational predictions, both in terms of single-chain compaction and propensity to undergo phase separation. We analyze the sequence features that determine changes in compaction and propensity to phase separate and find an overall good agreement with previous findings for naturally occurring sequences. Our general, physics-based method enables the design of disordered sequences with specified conformational properties. Our algorithm thus expands the toolbox for protein design to include also the most flexible proteins and will enable the design of proteins whose functions exploit the many properties afforded by protein disorder.

Global expression analysis of endometrial cancer cells in response to progesterone identifies new therapeutic targets.

Progesterone prevents development of endometrial cancers through its receptor (PR) although the molecular mechanisms have yet to be fully characterized. In this study, we performed a global analysis of gene regulation by progesterone using human endometrial cancer cells that expressed PR endogenously or exogenously. We found progesterone strongly inhibits multiple components of the platelet derived growth factor receptor (PDGFR), Janus kinase (JAK), signal transducer and activator of transcription (STAT) pathway through PR. The PDGFR/JAK/STAT pathway signals to control numerous downstream targets including AP-1 transcription factors Fos and Jun. Treatment with inhibitors of the PDGFR/JAK/STAT pathway significantly blocked proliferation in multiple novel patient-derived organoid models of endometrial cancer, and activation of this pathway was found to be a poor prognostic signal for the survival of patients with endometrial cancer from The Cancer Genome Atlas. Our study identifies this pathway as central to the growth-limiting effects of progesterone in endometrial cancer and suggests that inhibitors of PDGFR/JAK/STAT should be considered for future therapeutic interventions.

What kills the virtually immortal palms of the Florida scrub?

PREMISE: Life span varies greatly across plants, with some species being capable of extreme longevity. Yet even long-lived individuals are susceptible to climatic events, fire, and other challenges. We examined rare mortality events and their causes in two long-lived palmettos over four decades. METHODS: We monitored the survival of the clonal Serenoa repens and non-clonal, Florida-endemic Sabal etonia from 1981 to 2022 in four habitats along an elevational gradient within the globally imperiled Florida scrub ecosystem. We considered several challenges to palmetto survival, including extreme fires, shading due to lack of fire, droughts, periods of high precipitation, and possible pathogens. RESULTS: Survival of palmettos was remarkably high, and mortality was infrequent (Serenoa: cumulative, 5.7%; annualized, 0%-0.68%; Sabal: cumulative, 3.5%; annualized, 0%-0.43%). Mortality was highest in higher-elevation habitats with greater soil drainage, and smaller palmettos were more likely to die. When subjected to extreme fire, Serenoa suffered greater mortality than Sabal. Mortality in long-unburned habitats with increased shading rivaled that which occurred with extreme fire. There was no evidence of mortality due to lethal bronzing palm disease. CONCLUSIONS: Both palmettos had exceptionally low mortality rates, which, coupled with earlier work showing slow rates of transition from seedling to adult and remarkable adult longevity, suggest notably low rates of population turnover. Observed mortality in long-unburned habitats suggests the importance of fire-management planning with prescription burning. Lengthy age to reproduction and/or dependency on clonal propagation limits migration or genetic adaptation to altered conditions caused by climate change.

A PPIX-binding probe facilitates discovery of PPIX-induced cell death modulation by peroxiredoxin.

While heme synthesis requires the formation of a potentially lethal intermediate, protoporphyrin IX (PPIX), surprisingly little is known about the mechanism of its toxicity, aside from its phototoxicity. The cellular protein interactions of PPIX might provide insight into modulators of PPIX-induced cell death. Here we report the development of PPB, a biotin-conjugated, PPIX-probe that captures proteins capable of interacting with PPIX. Quantitative proteomics in a diverse panel of mammalian cell lines reveal a high degree of concordance for PPB-interacting proteins identified for each cell line. Most differences are quantitative, despite marked differences in PPIX formation and sensitivity. Pathway and quantitative difference analysis indicate that iron and heme metabolism proteins are prominent among PPB-bound proteins in fibroblasts, which undergo PPIX-mediated death determined to occur through ferroptosis. PPB proteomic data (available at PRIDE ProteomeXchange # PXD042631) reveal that redox proteins from PRDX family of glutathione peroxidases interact with PPIX. Targeted gene knockdown of the mitochondrial PRDX3, but not PRDX1 or 2, enhance PPIX-induced death in fibroblasts, an effect blocked by the radical-trapping antioxidant, ferrostatin-1. Increased PPIX formation and death was also observed in a T-lymphoblastoid ferrochelatase-deficient leukemia cell line, suggesting that PPIX elevation might serve as a potential strategy for killing certain leukemias.

The Effect of Parents and Peers on the Neural Correlates of Risk Taking and Antisocial Behavior During Adolescence.

Social and neurobiological factors independently associate with the development of antisocial behavior during adolescence, yet it is unclear how these factors contribute to antisocial behavior in girls. Using a longitudinal sample of 45 adolescent girls (age in years at scan: M = 15.38, SD = 0.33), this study examined the contributions of parent-adolescent relationship quality and deviant peer affiliation from 6th-8th grades along with the neural correlates of risk taking in 9th grade to later antisocial behavior. High parent-adolescent closeness in early adolescence predicted lower antisocial behavior for girls in later adolescence via lower affiliation with deviant peer groups and less activation of the medial prefrontal cortex during risk taking. Findings highlight the enduring role of parents and peers during adolescence, and the importance of investigating social relationships alongside the brain to identify a holistic understanding of the development of antisocial behavior in girls.

Life Engagement Improvement Following Initiation of Brexpiprazole Treatment in Patients with MDD: A Naturalistic, Retrospective Real-World Study.

Purpose: Life engagement encompasses concepts such as life fulfillment, well-being, and participation in meaningful activities, encompassing cognitive, physical, social, and emotional dimensions. Patients with MDD experience impaired functioning across multiple domains of life engagement and have ranked concepts related to life engagement and fulfillment as important predictors of treatment success. Post-hoc analyses of three clinical trials of patients with MDD treated adjunctively with brexpiprazole have reported a significantly greater improvement in life engagement. This study investigated improvements in life engagement among patients with MDD following initiation of brexpiprazole treatment using a real-world dataset. Patients and Methods: Information was extracted from semi-structured clinical notes of the Mental Status Examination (MSE) of patients in a real-world setting to develop an outcome measure for quantifying life engagement of psychiatric patients. Measures of life engagement and its four sub-domains (emotional, physical, social, and cognitive) were calculated at each clinical visit for 624 adult patients with MDD during the 6 months following brexpiprazole initiation. Paired t-tests assessed differences between the index event and time periods within 6 months of the index event. Kaplan-Meier survival analyses were used to quantify the improvement in life engagement scores following brexpiprazole initiation. Results: The study identified 54 clinical features associated with life engagement. Statistically significant improvements were observed from as early as 1 month following brexpiprazole initiation, with 20.6%, 37.9%, and 53.9% of the patients demonstrating improved life engagement scores within 1, 3, and 6 months, respectively. The improvements were particularly apparent for the emotional and social sub-domains. Conclusion: The results of this study provide evidence of improved life engagement following brexpiprazole initiation in a real-world dataset.

Assessment of models for calculating the hydrodynamic radius of intrinsically disordered proteins.

Diffusion measurements by pulsed-field gradient NMR and fluorescence correlation spectroscopy can be used to probe the hydrodynamic radius of proteins, which contains information about the overall dimension of a protein in solution. The comparison of this value with structural models of intrinsically disordered proteins is nonetheless impaired by the uncertainty of the accuracy of the methods for computing the hydrodynamic radius from atomic coordinates. To tackle this issue, we here build conformational ensembles of 11 intrinsically disordered proteins that we ensure are in agreement with measurements of compaction by small-angle x-ray scattering. We then use these ensembles to identify the forward model that more closely fits the radii derived from pulsed-field gradient NMR diffusion experiments. Of the models we examined, we find that the Kirkwood-Riseman equation provides the best description of the hydrodynamic radius probed by pulsed-field gradient NMR experiments. While some minor discrepancies remain, our results enable better use of measurements of the hydrodynamic radius in integrative modeling and for force field benchmarking and parameterization.

The Relative Effects of Instruction Linking Word Reading and Word Meaning Compared to Word Reading Instruction Alone on the Accuracy, Fluency, and Word Meaning Knowledge of 4th-5th Grade Students With Dyslexia.

This within-subjects experimental study investigated the relative effects of word reading and word meaning instruction (WR+WM) compared to word-reading instruction alone (WR) on the accuracy, fluency, and word meaning knowledge of 4th-5th graders with dyslexia. We matched word lists on syllables, phonemes, frequency, number of definitions, and concreteness. We assigned half the words to WR and half to WR+WM. Word reading accuracy, word reading fluency, and word meaning knowledge were measured at pretest, immediately following each intervention session, and at posttest, administered immediately following the 12, 45-minute, daily instructional sessions. Compared to WR instruction alone, WR+WM significantly improved accuracy (d = 0.65), fluency (d = 0.43), and word meaning knowledge (d = 1.92) immediately following intervention, and significantly improved accuracy (d = 0.74), fluency (d = 0.84), and word meaning knowledge (d = 1.03) at posttest. Findings support the premise that word meaning knowledge facilitates accurate and fluent word reading, and that instruction explicitly integrating word reading and word meaning may be an effective support for upper elementary students with dyslexia.

Characterization of HCI-EC-23 a novel estrogen- and progesterone-responsive endometrial cancer cell line.

Most endometrial cancers express the hormone receptor estrogen receptor alpha (ER) and are driven by excess estrogen signaling. However, evaluation of the estrogen response in endometrial cancer cells has been limited by the availability of hormonally responsive in vitro models, with one cell line, Ishikawa, being used in most studies. Here, we describe a novel, adherent endometrioid endometrial cancer (EEC) cell line model, HCI-EC-23. We show that HCI-EC-23 retains ER expression and that ER functionally responds to estrogen induction over a range of passages. We also demonstrate that this cell line retains paradoxical activation of ER by tamoxifen, which is also observed in Ishikawa and is consistent with clinical data. The mutational landscape shows that HCI-EC-23 is mutated at many of the commonly altered genes in EEC, has relatively few copy-number alterations, and is microsatellite instable high (MSI-high). In vitro proliferation of HCI-EC-23 is strongly reduced upon combination estrogen and progesterone treatment. HCI-EC-23 exhibits strong estrogen dependence for tumor growth in vivo and tumor size is reduced by combination estrogen and progesterone treatment. Molecular characterization of estrogen induction in HCI-EC-23 revealed hundreds of estrogen-responsive genes that significantly overlapped with those regulated in Ishikawa. Analysis of ER genome binding identified similar patterns in HCI-EC-23 and Ishikawa, although ER exhibited more bound sites in Ishikawa. This study demonstrates that HCI-EC-23 is an estrogen- and progesterone-responsive cell line model that can be used to study the hormonal aspects of endometrial cancer.

Small molecule SJ572946 activates BAK to initiate apoptosis.

Poration of the outer mitochondrial membrane by the effector BCL-2 proteins BAK and BAX initiates apoptosis. BH3-only initiators BID and BIM trigger conformational changes in BAK and BAX transforming them from globular dormant proteins to oligomers of the apoptotic pores. Small molecules that can directly activate effectors are being sought for applications in cancer treatment. Here, we describe the small molecule SJ572946, discovered in a fragment-based screen that binds to the activation groove of BAK and selectively triggers BAK activation over that of BAX in liposome and mitochondrial permeabilization assays. SJ572946 independently kills BAK-expressing BCL2allKO HCT116 cells revealing on target cellular activity. In combination with apoptotic inducers and BH3 mimetics, SJ572946 kills experimental cancer cell lines. SJ572946 also cooperates with the endogenous BAK activator BID in activating a misfolded BAK mutant substantially impaired in activation. SJ572946 is a proof-of-concept tool for probing BAK-mediated apoptosis in preclinical cancer research.

The Impact of Agitation in Dementia on Caregivers: A Real-World Survey.

BACKGROUND: Dementia patients frequently depend on caregivers. Agitation is a common behavioral dementia symptom particularly burdensome to patients and caregivers. OBJECTIVE: To assess the association of agitation severity with non-professional caregiver hours, burden, health status, and productivity. Secondarily, to assess the association of agitation severity with these outcomes for patients receiving remote (not living with the patient) and proximate (living with the patient) caregiving. METHODS: A retrospective analysis of physician and non-professional caregiver-reported data from a US point-in-time survey. Patients were aged ≥50 years, with early cognitive impairment or dementia. Regression analyses compared outcomes by agitation severity; covariates included age, sex, and clinical characteristics. RESULTS: Data were included for 1,349 patients (non-agitated n = 656, agitated n = 693; no care n = 305, remote care n = 248, proximate care n = 691; unknown care n = 105). Greater agitation was significantly associated (p < 0.05) in all caregivers with increasing: Zarit Burden Interview (ZBI) Total Caregiver Burden, Personal Strain, Role Strain, and Guilt; Work Productivity and Activity Index (WPAI) presenteeism, overall work impairment, and total activity impairment. Higher ZBI Total Caregiver Burden, Personal Strain, and Role Strain were associated with greater agitation in proximate caregivers and higher ZBI Guilt associated with greater agitation in remote caregivers (p < 0.05). Higher WPAI presenteeism and total activity impairment were associated (p < 0.05) with greater agitation in proximate caregivers. Caregiving hours increased with increasing agitation for proximate caregiving (p = 0.001). CONCLUSION: Greater agitation severity was associated with higher caregiver burden and lower productivity, with higher indirect costs a likely outcome of agitation.

Benign Neonatal Hemangiomatosis.

BACKGROUND: Benign neonatal hemangiomatosis (BNH) is a rare, self-limiting subtype of infantile hemangiomas (IHs), in which infants with multiple cutaneous hemangiomas lack visceral involvement. Other subtypes of IHs exist that may mimic BNH and can be life-threatening depending on hemangioma location and size. CLINICAL FINDINGS: At birth, a 29 5 / 7 -week preterm female presented with several pinhead-sized pink papules distributed throughout her body. At 10 days of age, the patient had 12 enlarged domed-shaped red papules in a generalized distribution throughout her body. Over several weeks, the number and size of the domed-shaped red papules continued to increase to a total of 26 located on the head, chest, abdomen, back, legs and arms. They were of firm consistency with both smooth and lobulated surfaces. PRIMARY DIAGNOSIS: A diagnosis of BNH was made after extensive workup did not reveal any extracutaneous hemangiomas. INTERVENTIONS: Due to the lack of extracutaneous involvement and low-risk location/size of hemangiomas in our patient, no interventions were pursued and an observation-only approach was implemented. OUTCOMES: The patient remained stable while followed up over 8 months, with the size of the hemangiomas only increasing slightly in proportion to the patient's natural body growth. PRACTICE RECOMMENDATIONS: Given the life-threatening nature of certain hemangioma subtypes, it is important to implement a proper workup and subtype diagnosis as early as possible in any infant with multiple hemangiomas.

The Economic Burden of Posttraumatic Stress Disorder in the United States From a Societal Perspective.

Objective: To estimate the economic burden of posttraumatic stress disorder (PTSD) in the United States civilian and military populations from a societal perspective.Methods: A prevalence-based and human capital approach was used to estimate the total excess costs of PTSD in 2018 from insurance claims data, academic literature, and governmental publications. Excess direct health care costs (pharmacy, medical), direct non-health care costs (research and training, substance use, psychotherapy, homelessness, disability), and indirect costs (unemployment, productivity loss, caregiving, premature mortality) associated with PTSD were compared between adults with PTSD and adults without PTSD, or the general population if information was not available for adults without PTSD.Results: The total excess economic burden of PTSD in the US was estimated at $232.2 billion for 2018 ($19,630 per individual with PTSD). Total excess costs were $189.5 billion (81.6%) in the civilian population and $42.7 billion (18.4%) in the military population, corresponding to $18,640 and $25,684 per individual with PTSD in the civilian and military populations, respectively. In the civilian population, the excess burden was driven by direct health care ($66.0 billion) and unemployment ($42.7 billion) costs. In the military population, the excess burden was driven by disability ($17.8 billion) and direct health care ($10.1 billion) costs.Conclusions: The economic burden of PTSD goes beyond direct health care costs and has been found to rival costs for other costly mental health conditions. Increased awareness of PTSD, development of more effective therapies, and expansion of evidence-based interventions may be warranted to reduce the large clinical and economic burden of PTSD.

Neural connectivity underlying adolescent social learning in sibling dyads.

Social learning theory posits that adolescents learn to adopt social norms by observing the behaviors of others and internalizing the associated outcomes. However, the underlying neural processes by which social learning occurs is less well-understood, despite extensive neurobiological reorganization and a peak in social influence sensitivity during adolescence. Forty-four adolescents (Mage = 12.2 years) completed an fMRI scan while observing their older sibling within four years of age (Mage = 14.3 years) of age complete a risky decision-making task. Group iterative multiple model estimation (GIMME) was used to examine patterns of directional brain region connectivity supporting social learning. We identified group-level neural pathways underlying social observation including the anterior insula to the anterior cingulate cortex and mentalizing regions to social cognition regions. We also found neural states based on adolescent sensitivity to social learning via age, gender, modeling, differentiation, and behavior. Adolescents who were more likely to be influenced elicited neurological up-regulation whereas adolescents who were less likely to be socially influenced elicited neurological down-regulation during risk-taking. These findings highlight patterns of how adolescents process information while a salient influencer takes risks, as well as salient neural pathways that are dependent on similarity factors associated with social learning theory.

Identification of structural transitions in bacterial fatty acid binding proteins that permit ligand entry and exit at membranes.

Fatty acid (FA) transfer proteins extract FA from membranes and sequester them to facilitate their movement through the cytosol. Detailed structural information is available for these soluble protein-FA complexes, but the structure of the protein conformation responsible for FA exchange at the membrane is unknown. Staphylococcus aureus FakB1 is a prototypical bacterial FA transfer protein that binds palmitate within a narrow, buried tunnel. Here, we define the conformational change from a "closed" FakB1 state to an "open" state that associates with the membrane and provides a path for entry and egress of the FA. Using NMR spectroscopy, we identified a conformationally flexible dynamic region in FakB1, and X-ray crystallography of FakB1 mutants captured the conformation of the open state. In addition, molecular dynamics simulations show that the new amphipathic α-helix formed in the open state inserts below the phosphate plane of the bilayer to create a diffusion channel for the hydrophobic FA tail to access the hydrocarbon core and place the carboxyl group at the phosphate layer. The membrane binding and catalytic properties of site-directed mutants were consistent with the proposed membrane docked structure predicted by our molecular dynamics simulations. Finally, the structure of the bilayer-associated conformation of FakB1 has local similarities with mammalian FA binding proteins and provides a conceptual framework for how these proteins interact with the membrane to create a diffusion channel from the FA location in the bilayer to the protein interior.

Structural basis of BAK activation in mitochondrial apoptosis initiation.

BCL-2 proteins regulate mitochondrial poration in apoptosis initiation. How the pore-forming BCL-2 Effector BAK is activated remains incompletely understood mechanistically. Here we investigate autoactivation and direct activation by BH3-only proteins, which cooperate to lower BAK threshold in membrane poration and apoptosis initiation. We define in trans BAK autoactivation as the asymmetric "BH3-in-groove" triggering of dormant BAK by active BAK. BAK autoactivation is mechanistically similar to direct activation. The structure of autoactivated BAK BH3-BAK complex reveals the conformational changes leading to helix α1 destabilization, which is a hallmark of BAK activation. Helix α1 is destabilized and restabilized in structures of BAK engaged by rationally designed, high-affinity activating and inactivating BID-like BH3 ligands, respectively. Altogether our data support the long-standing hit-and-run mechanism of BAK activation by transient binding of BH3-only proteins, demonstrating that BH3-induced structural changes are more important in BAK activation than BH3 ligand affinity.