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Physical interactions between polypeptide chains and lipid membranes underlie critical cellular processes. Yet, despite fundamental importance, key mechanistic aspects of these interactions remain elusive. Bulk experiments have revealed a linear relationship between free energy and peptide chain length in a model system, but does this linearity extend to the interaction strength and to the kinetics of lipid binding? To address these questions, we utilized a combination of coarse-grained molecular dynamics (CG MD) simulations, analytical modeling, and atomic force microscopy (AFM)-based single molecule force spectroscopy. Following previous bulk experiments, we focused on interactions between short hydrophobic peptides (WLn, n= 1, ..., 5) with 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) bilayers, a simple system that probes peptide primary structure effects. Potentials of mean force extracted from CG MD recapitulated the linearity of free energy with the chain length. Simulation results were quantitatively connected to bulk biochemical experiments via a single scaling factor of order unity, corroborating the methodology. Additionally, CG MD revealed an increase in the distance to the transition state, a result that weakens the dependence of the dissociation force on the peptide chain length. AFM experiments elucidated rupture force distributions and, through modeling, intrinsic dissociation rates. Taken together, the analysis indicates a rupture force plateau in the WLn–POPC system, suggesting that the final rupture event involves the last 2 or 3 residues. In contrast, the linear dependence on chain length was preserved in the intrinsic dissociation rate. This study advances the understanding of peptide–lipid interactions and provides potentially useful insights for the design of peptides with tailored membrane-interacting properties.

Frailty is a complex clinical syndrome associated with aging and comorbidities, which correlates with unfavorable outcomes. However, in heart failure patients, frailty is very common, data is scarce about those, who are eligible for Cardiac Resynchronization Therapy (CRT) implantation. We investigated the incidence of frailty and the association of Frailty Index (FI) with the outcome. Thirty baseline clinical parameters were used by the Rockwood cumulative deficit method to determine patients' FI in our single-center cohort. Based on previous studies, patients with FI ≤ 0.210 were considered as non-frail, those with FI 0.10–0.210 were classified in Frail-1, with FI > 0.10 in Frail-2 groups, respectively. Echocardiographic response after 12 months and all-cause mortality were investigated by frailty groups. Among 1004 included patients, 75 (7%) were considered Non-frail, 271 (27%) grouped in Frail-1, and 658 (66%) in Frail-2 with a median FI of 0.36 (0.28–0.43). Patients in Frail-2 group were older, with more comorbidities compared with non-frail patients or those in Group Frail-1. During the median follow-up time of 4.8 years, 29 (39%) patients died in the Non-frail, 140 (52%) in Frail-1, and 471 (72%) in the Frail-2 groups (log-rank p< 0.001). Group Frail-2 showed an unfavorable outcome compared to the non-frail (HR 2.49, 95%CI 1.92–3.22; p< 0.001) and the Frail-1 group (1.83, 95%CI 1.55–2.16; p< 0.001). In our HFrEF patients eligible for CRT implantation, patients were exceedingly vulnerable with a high prevalence of frailty. The calculated frailty index was associated with outcome and proved to be prevalent in individual risk stratification.

Heart failure (HF) is a leading cause of mortality and hospitalization in the elderly. However, data are scarce about their response to device treatment such as cardiac resynchronization therapy (CRT). We aimed to evaluate the age-related differences in the effectiveness of CRT, procedure-related complications, and long-term outcome. Between 2000 and 2020, 2656 patients undergoing CRT implantation were registered and analyzed retrospectively. Patients were divided into 3 groups according to their age: group I, < 65; group II, 65–75; and group III, > 75 years. The primary endpoint was the echocardiographic response defined as a relative increase > 15% in left ventricular ejection fraction (LVEF) within 6 months, and the secondary endpoint was the composite of all-cause mortality, heart transplantation, or left ventricular assist device implantation. Procedure-related complications were also assessed. After implantation, LVEF showed significant improvement both in the total cohort [28% (IQR24/33) vs. 35% (IQR28/40); p< 0.01)] and in each subgroup (27% vs. 34%; p< 0.01, 29% vs. 35%; p< 0.01, 30% vs. 35%; p< 0.01). Response rate was similar in the 3 groups (64% vs. 62% vs. 56%; p= 0.41). During the follow-up, 1574 (59%) patients died. Kaplan–Meier curves revealed a significantly lower survival rate in the older groups (log-rank p< 0.001). The cumulative complication rates were similar among the three age groups (27% vs. 28% vs. 24%; p= 0.15). Our results demonstrate that CRT is as effective and safe therapy in the elderly as for young ones. The present data suggest that patients with appropriate indications benefit from CRT in the long term, regardless of age.

The use of technology is increasing rapidly in our society, and classroom teachers must recognize the impact and importance of technology in the lives of their students. It is crucial that college faculty involved in teacher training design courses that integrate mobile technologies to prepare the next generation of teachers. In this study, we investigate the effectiveness of an iPadbased curriculum app, Exploring Physics, to enhance preservice elementary teachers’ physics conceptual understanding in a physical science content course. Data were collected using a pre-andpostPhysics Conceptual Understanding (PCU) survey and open-ended questionnaires. We found significant statistical gains in participants’ (N = 73) physics conceptual understanding at the end of the course. Qualitative findings suggest that the learning experience allowed participants to experience the pedagogical affordances of mobile technologies as learners and future teachers and found themselves to be more comfortable with the idea of integrating technology into their future classrooms. The results of this study provide insights into the importance of providing preservice teachers with opportunities to experience the use of mobile technologies in their teacher preparation programs.

Quantitative characterization of the strength of peripheral membrane protein–lipid bilayer interactions is fundamental in the understanding of many protein targeting pathways. SecA is a peripheral membrane protein that plays a central role in translocating precursor proteins across the inner membrane of E. coli. The membrane binding activity of the extreme N-terminus of SecA is critical for translocase function. Yet, the mechanical strength of the interaction and the kinetic pathways that this segment of SecA experiences when in proximity of an E. colipolar lipid bilayer has not been characterized. We directly measured the N-terminal SecA-lipid bilayer interaction using precision single molecule atomic force microscope (AFM)-based dynamic force spectroscopy. To provide conformational data inaccessible to AFM, we also performed all-atom molecular dynamics simulations and circular dichroism measurements. The N-terminal 10 amino acids of SecA have little secondary structure when bound to zwitterionic lipid head groups, but secondary structure, which rigidifies the lipid-bound protein segment, emerges when negatively charged lipids are present. Analysis of the single molecule protein–lipid dissociation data converged to a well-defined lipid-bound-state lifetime in the absence of force, τ0lipid= 0.9 s, which is well separated from and longer than the fundamental time scale of the secretion process, defined as the time required to translocate a single amino acid residue (∼50 ms). This value of τ0lipidis likely to represent a lower limit of the in vivomembrane-bound lifetime due to factors including the minimal system employed here.

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The authors aimed to evaluate the association of left ventricular (LV) lead location and long-term outcomes in MADIT-CRT (Multicenter Automatic Defibrillator Implantation With Cardiac Resynchronization Therapy).

AbstractContext:Assessment of response to cardiac resynchronization therapy (CRT) is essential.Objective:To assess the predictive value of CT-apelin together with NT-proBNP in patients undergoing CRT.Methods:Serum CT-apelin and NT-proBNP were measured by ELISA before, and six months after CRT. Primary endpoint was non-response (<4% increase in LVEF) after six months.Results:From 81 patients, 15 proved to be non-responders. Six-month CT-apelin was superior compared to NT-proBNP in identifying non-responders by multivariate ROC (CT-apelin: p = 0.01, NT-proBNP: p = 0.13) and by logistic regression (CT-apelin: p = 0.01, NT-proBNP: p = 0.41) analyses.Conclusion:Six-month CT-apelin might be a valuable novel biomarker in identifying non-responders to CRT that was superior to NT-proBNP.

Tissue engineering is a rapidly evolving discipline that aims at building functional tissues to improve or replace damaged ones. To be successful in such an endeavor, ideally, the engineering of tissues should be based on the principles of developmental biology. Recent progress in developmental biology suggests that the formation of tissues from the composing cells is often guided by physical laws. Here a comprehensive computational-theoretical formalism is presented that is based on experimental input and incorporates biomechanical principles of developmental biology. The formalism is described and it is shown that it correctly reproduces and predicts the quantitative characteristics of the fundamental early developmental process of tissue fusion. Based on this finding, the formalism is then used toward the optimization of the fabrication of tubular multi- cellular constructs, such as a vascular graft, by bioprinting, a novel tissue engineering technology. [ABSTRACT FROM AUTHOR]

The fundamental processes by which proteins recognize and bind to nucleic acids are critical to understanding cellular function. To explore the factors involved in protein-DNA recognition, we used hydrostatic pressure to perturb the binding of the BamHI endonuclease to cognate DNA, both in experiment and in molecular dynamic simulations. A new technique of high-pressure gel mobility shift analysis was used to test the effects of elevated hydrostatic pressure on the binding of BamHI to its cognate recognition sequence. Upon application of a pressure of 500 bar, the equilibrium dissociation constant of BamHI binding to the cognate site was found to increase nearly 10-fold. A challenge has been to link this type of pure thermodynamic measurement to functional events occurring at the molecular level. Thus, we used molecular dynamic simulations at both ambient and elevated pressures to reveal details of the direct and water-mediated interactions between BamHI and cognate DNA, which allow explanation of the effects of pressure on site-specific protein-DNA binding and complex stability.

The mechanosensitive channel of large conductance (MscL) in prokaryotes plays a crucial role in exocytosis as well as in the response to osmotic downshock. The channel can be gated by tension in the membrane bilayer. The determination of functionally important residues in MscL, patch-clamp studies of pressure-conductance relationships, and the recently elucidated crystal structure of MscL from Mycobacterium tuberculosis have guided the search for the mechanism of MscL gating. Here, we present a molecular dynamics study of the MscL protein embedded in a fully hydrated POPC bilayer. Simulations totaling 3ns in length were carried out under conditions of constant temperature and pressure using periodic boundary conditions and full electrostatics. The protein remained in the closed state corresponding to the crystal structure, as evidenced by its impermeability to water. Analysis of equilibrium fluctuations showed that the protein was least mobile in the narrowest part of the channel. The gating process was investigated through simulations of the bare protein under conditions of constant surface tension. Under a range of conditions, the transmembrane helices flattened as the pore widened. Implications for the gating mechanism in light of these and experimental results are discussed.

Retinoic acid receptor (RAR) is a ligand-dependent transcription factor that regulates the expression of genes involved in cell growth, differentiation, and development. Binding of the retinoic acid hormone to RAR is accompanied by conformational changes in the protein which induce transactivation or transrepression of the target genes. In this paper we present a study of the hormone binding/unbinding process in order to clarify the role of some of the amino acid contacts and identify possible pathways of the all-trans retinoic acid binding/unbinding to/from human retinoic acid receptor (hRAR)-γ. Three possible pathways were explored using steered molecular dynamics simulations. Unbinding was induced on a time scale of 1ns by applying external forces to the hormone. The simulations suggest that the hormone may employ one pathway for binding and an alternative “back door” pathway for unbinding.

Molecular dynamics simulations were performed on models of the dodecamer DNA double-stranded segment, [d(CGCGAATTCGCG)](2), in which each of the adenine residues, individually or jointly, was replaced by the water-mimicking analog 2'-deoxy-7-(hydroxy-methyl)-7-deazaadenosine (hm(7)c(7)dA) [Rockhill, J.K., Wilson,S.R. and Gumport,R.I. (1996) J. Am. Chem. Soc.,118, 10065-10068]. The simulations, when compared with those of the dodecamer itself, show that incorporation of the analog affects neither the overall DNA structure nor its hydrogen-bonding and stacking interactions when it replaces a single individual base. Furthermore, the water molecules near the bases in the singly-substituted oligonucleotides are similarly unaffected. Double substitutions lead to differences in all the aforementioned parameters with respect to the reference sequence. The results suggest that the analog provides a good mimic of specific 'ordered' water molecules observed in contact with DNA itself and at the interface between protein and DNA in specific complexes.

Purpose: Cardiac deconditioning due to immobilization is a risk factor for cardiovascular disease. The physiology of cardiac adaptation to deconditioning has not been fully elucidated. The purpose of the present study was to assess the effects of 21-days of strict head-down (-6 degrees) bed-rest (BR) deconditioning on left ventricular (LV) dimensions and mass measured by MRI. Methods: Ten healthy men (mean age 32±6) were enrolled; the experiment was conducted at DLR (Koln, Germany) as part of the European Space Agency BR studies. Steady-state free precession MRI images (7mm thickness, no gap, no overlap) were obtained (Symphony 1.5T, Siemens) in a stack of short-axis views from LV base to LV apex, before (PRE), at the end of BR (HDT20), and four days after the BR conclusion (POST). Endocardial and epicardial semi-automated contouring was performed using freely available software (Segment). Results: At HDT20, significant reductions in LV mass (16%), end-diastolic (26%) and end-systolic (27%) volumes and stroke volume (27%) were observed, while ejection fraction did not change. These changes were accompanied by a measured decrease (14%) in plasma and blood volume (by gas-rebreathing technique), as well as by a significant reduction (14%) in VO2max aerobic power, measured using a graded cycle ergometer test protocol to volitional fatigue, at one day after the BR conclusion, while expiratory exchange ratio did not change. At POST, LV volumes were restored, while LV mass was still trending towards control values. Conclusions: Cardiac adaptation to deconditioning affected LV mass and dimensions, as a combined result of LV remodeling and fluids loss, accompanied by worsening in aerobic power. This should be taken into account in patients with cardiovascular diseases, when immobilized in bed, to proper adjust the therapy, or to define appropriate physical exercises when possible, in order to avoid further complications.   Cardiac MRI parameters PREHDT20POSTLV mass (g)121±6102±11*114±16End-diastolic volume (ml)119±2590±14*118±25End-systolic volume (ml)42±831±8*45±14Stroke volume (ml)76±2259±11*73±15Ejection fraction (%)64±665±762±7 *: p<.01 vs PRE (one-way Anova for paired data and Tukey test)