Transmembrane communication: general principles and lessons from the structure and function of the M2 proton channel, K⁺ channels, and integrin receptors.

Signal transduction across biological membranes is central to life. This process generally happens through communication between different domains and hierarchical coupling of information. Here, we review structural and thermodynamic principles behind transmembrane (TM) signal transduction and discuss common themes. Communication between signaling domains can be understood in terms of thermodynamic and kinetic principles, and complex signaling patterns can arise from simple wiring of thermodynamically coupled domains. We relate this to functions of several signal transduction systems: the M2 proton channel from influenza A virus, potassium channels, integrin receptors, and bacterial kinases. We also discuss key features in the structural rearrangements responsible for signal transduction in these systems.

Increasing buprenorphine access for veterans with opioid use disorder in rural clinics using telemedicine.

Background:Having prescribers use clinical video teleconferencing (telemedicine) to prescribe buprenorphine to people with opioid use disorder (OUD) has shown promise but its implementation is challenging. We describe barriers, facilitators and lessons learned while implementing a system to remotely prescribe buprenorphine to Veterans in rural settings. Methods: We conducted a quality improvement project aimed at increasing the availability of medications for OUD (MOUD) to Veterans. This project focused on tele-prescribing buprenorphine to rural sites via a hub (centralized prescribers) and spoke (rural clinics) model. After soliciting a wide-range of inputs from site visits, qualitative interviews of key stakeholders at rural sites, and review of preliminary cases, a "how-to" toolkit was developed and iteratively refined to guide tele-prescribing of buprenorphine. After internal and external facilitation strategies were employed, Veterans with OUD at three clinics were transitioned to buprenorphine treatment via telemedicine. Results: Factors impacting adoption of the tele-prescribing intervention were mapped to the Consolidated Framework for Implementation Research (CFIR) constructs. Barriers to adoption included concerns about legality of tele-prescribing a controlled substance, conflicting interests between different stakeholders, and coordination with an existing buprenorphine program requiring more attendance and abstinence from Veterans than the tele-prescribing program required. Factors facilitating adoption included a sense of mission around combating the opioid epidemic, preexisting use of and comfort with tele-prescribing, and rural sites' control over Veterans referred to tele-prescribers. A total of 12 patients from rural areas were successfully transitioned onto buprenorphine, of whom 9 remained on buprenorphine 6 months after initiation of treatment. Conclusions: Implementing tele-prescribing was negotiated with stakeholders at the target clinics and operationalized in a toolkit to guide future efforts. Implementation issues can be addressed by activities that foster collaboration between hubs (centralized prescribers) and spokes (rural clinics) and by a toolkit that operationalizes tele-prescribing procedures.

The intertwined expansion of telehealth and buprenorphine access from a prescriber hub.

In this manuscript, we describe how efforts to increase access to buprenorphine for Opioid Use Disorder (OUD) through a telemedicine hub before and since the COVID-19 pandemic have played out in the Veterans Healthcare Administration (VHA) in New England. We look at how the COVID-19 pandemic and subsequent spike in opioid overdoses tilted the risk: benefit calculation for tele-prescribing a controlled substance such as buprenorphine toward expanding access to tele-buprenorphine. We conclude that there is a need for tele-buprenorphine hubs that can fill gaps in geographically dispersed healthcare systems.

Medical-Surgical Hospitalization Among Veterans With Psychiatric and Substance Use Disorders.

BACKGROUND: Mental illness is associated with an increased risk for medical hospitalizations. OBJECTIVE: This study investigates the degree to which nonpsychiatric factors account for these hospitalizations. METHODS: Using National Veterans Health Administration (VHA) fiscal year 2012 data for 2 million veterans under the age of 60 years, hospitalization risks were compared for veterans with and without mental illnesses. Bivariate analyses identified factors associated with mental illnesses. Multiple logistic regression was used to calculate adjusted psychiatric risk for medical hospitalization, controlling for these factors. RESULTS: Veterans carrying mental health diagnoses were at increased risk for hospitalizations (odds ratio [OR] = 2.52, 2.48-2.55). Among individual diagnoses, alcohol use disorder (AUD) (OR = 3.84, 3.78-3.91) and drug use disorders (OR = 4.58, 4.50-4.66) were associated with the highest risk. After adjusting for nonpsychiatric medical, addiction-related, and care utilization factors and the use of outpatient medical services, veterans with mental illnesses were at increased risk for medical hospitalization (OR = 1.43, 1.41-1.45). After further adjustment for AUD and drug use, hospitalization risk decreased further (OR = 1.23, 1.21-1.26) while the association of AUD and hospitalizations remained high (OR = 1.77, 1.73-1.81). CONCLUSIONS: Medical comorbidities and service use accounted for most, but not all, of the increased risk of medical hospitalizations associated with mental illness. Even after accounting for poor health, AUD remained strongly associated with medical hospitalization.

A Focused Addiction Curriculum and Its Impact on Student Knowledge, Attitudes, and Confidence in the Treatment of Patients with Substance Use.

BACKGROUND: Assessment of attitudes towards addiction in medical students has largely gone unexplored. This study examines the impact of a supplemental substance use disorder curriculum in the psychiatry clerkship on medical student attitudes towards addiction. METHODS: The curriculum was only administered to students at one clerkship site. Subsequently, medical students were surveyed across all sites regarding their attitudes towards addiction. RESULTS: The survey response rate was 37.5% (N = 75/200), with 25 (33%) completing the supplemental addiction curriculum. In bivariate analysis, medical students receiving the curriculum were more likely to express confidence in managing patients with alcohol and opiate use disorders (T = 2.01, p = 0.05) and were more knowledgeable about Alcoholics Anonymous (AA) as a treatment option available to patients (T = 2.27, p = 0.03). CONCLUSIONS: A supplemental addiction curriculum can improve medical student confidence in managing substance-using patients as well as improve knowledge of AA.

Directly Activating the Integrin αIIbß3 Initiates Outside-In Signaling by Causing αIIbß3 Clustering.

αIIbß3 activation in platelets is followed by activation of the tyrosine kinase c-Src associated with the carboxyl terminus of the ß3 cytosolic tail. Exogenous peptides designed to interact with the αIIb transmembrane (TM) domain activate single αIIbß3 molecules in platelets by binding to the αIIb TM domain and causing separation of the αIIbß3 TM domain heterodimer. Here we asked whether directly activating single αIIbß3 molecules in platelets using the designed peptide anti-αIIb TM also initiates αIIbß3-mediated outside-in signaling by causing activation of ß3-associated c-Src. Anti-αIIb TM caused activation of ß3-associated c-Src and the kinase Syk, but not the kinase FAK, under conditions that precluded extracellular ligand binding to αIIbß3. c-Src and Syk are activated by trans-autophosphorylation, suggesting that activation of individual αIIbß3 molecules can initiate αIIbß3 clustering in the absence of ligand binding. Consistent with this possibility, incubating platelets with anti-αIIb TM resulted in the redistribution of αIIbß3 from a homogenous ring located at the periphery of discoid platelets into nodular densities consistent with clustered αIIbß3. Thus, these studies indicate that not only is resting αIIbß3 poised to undergo a conformational change that exposes its ligand-binding site, but it is poised to rapidly assemble into intracellular signal-generating complexes as well.

Synthesis and Spectroscopy of Silver-Doped PbSe Quantum Dots.

Electronic impurity doping of bulk semiconductors is an essential component of semiconductor science and technology. Yet there are only a handful of studies demonstrating control of electronic impurities in semiconductor nanocrystals. Here, we studied electronic impurity doping of colloidal PbSe quantum dots (QDs) using a postsynthetic cation exchange reaction in which Pb is exchanged for Ag. We found that varying the concentration of dopants exposed to the as-synthesized PbSe QDs controls the extent of exchange. The electronic impurity doped QDs exhibit the fundamental spectroscopic signatures associated with injecting a free charge carrier into a QD under equilibrium conditions, including a bleach of the first exciton transition and the appearance of a quantum-confined, low-energy intraband absorption feature. Photoelectron spectroscopy confirms that Ag acts as a p-type dopant for PbSe QDs and infrared spectroscopy is consistent with k·p calculations of the size-dependent intraband transition energy. We find that to bleach the first exciton transition by an average of 1 carrier per QD requires that approximately 10% of the Pb be replaced by Ag. We hypothesize that the majority of incorporated Ag remains at the QD surface and does not interact with the core electronic states of the QD. Instead, the excess Ag at the surface promotes the incorporation of <1% Ag into the QD core where it causes p-type doping behavior.

The Tyrosine Kinase c-Src Specifically Binds to the Active Integrin αIIbß3 to Initiate Outside-in Signaling in Platelets.

It is currently believed that inactive tyrosine kinase c-Src in platelets binds to the cytoplasmic tail of the ß3 integrin subunit via its SH3 domain. Although a recent NMR study supports this contention, it is likely that such binding would be precluded in inactive c-Src because an auto-inhibitory linker physically occludes the ß3 tail binding site. Accordingly, we have re-examined c-Src binding to ß3 by immunoprecipitation as well as NMR spectroscopy. In unstimulated platelets, we detected little to no interaction between c-Src and ß3. Following platelet activation, however, c-Src was co-immunoprecipitated with ß3 in a time-dependent manner and underwent progressive activation as well. We then measured chemical shift perturbations in the (15)N-labeled SH3 domain induced by the C-terminal ß3 tail peptide NITYRGT and found that the peptide interacted with the SH3 domain RT-loop and surrounding residues. A control peptide whose last three residues where replaced with those of the ß1 cytoplasmic tail induced only small chemical shift perturbations on the opposite face of the SH3 domain. Next, to mimic inactive c-Src, we found that the canonical polyproline peptide RPLPPLP prevented binding of the ß3 peptide to the RT- loop. Under these conditions, the ß3 peptide induced chemical shift perturbations similar to the negative control. We conclude that the primary interaction of c-Src with the ß3 tail occurs in its activated state and at a site that overlaps with PPII binding site in its SH3 domain. Interactions of inactive c-Src with ß3 are weak and insensitive to ß3 tail mutations.

Crystallization kinetics of organic-inorganic trihalide perovskites and the role of the lead anion in crystal growth.

Methylammonium lead halide perovskite solar cells continue to excite the research community due to their rapidly increasing performance which, in large part, is due to improvements in film morphology. The next step in this progression is control of the crystal morphology which requires a better fundamental understanding of the crystal growth. In this study we use in situ X-ray scattering data to study isothermal transformations of perovskite films derived from chloride, iodide, nitrate, and acetate lead salts. Using established models we determine the activation energy for crystallization and find that it changes as a function of the lead salt. Further analysis enabled determination of the precursor composition and showed that the primary step in perovskite formation is removal of excess organic salt from the precursor. This understanding suggests that careful choice of the lead salt will aid in controlling crystal growth, leading to superior films and better performing solar cells.

Affinity of talin-1 for the ß3-integrin cytosolic domain is modulated by its phospholipid bilayer environment.

Binding of the talin-1 FERM (4.1/ezrin/radixin/moesin) domain to the ß3 cytosolic tail causes activation of the integrin αIIbß3. The FERM domain also binds to acidic phospholipids. Although much is known about the interaction of talin-1 with integrins and lipids, the relative contribution of each interaction to integrin regulation and possible synergy between them remain to be clarified. Here, we examined the thermodynamic interplay between FERM domain binding to phospholipid bilayers and to its binding sites in the ß3 tail. We found that although both the F0F1 and F2F3 subdomains of the talin-1 FERM domain bind acidic bilayers, the full-length FERM domain binds with an affinity similar to F2F3, indicating that F0F1 contributes little to the overall interaction. When free in solution, the ß3 tail has weak affinity for the FERM domain. However, appending the tail to acidic phospholipids increased its affinity for the FERM domain by three orders of magnitude. Nonetheless, the affinity of the FERM for the appended tail was similar to its affinity for binding to bilayers alone. Thus, talin-1 binding to the ß3 tail is a ternary interaction dominated by a favorable surface interaction with phospholipid bilayers and set by lipid composition. Nonetheless, interactions between the FERM domain, the ß3 tail, and lipid bilayers are not optimized for a high-affinity synergistic interaction, even at the membrane surface. Instead, the interactions appear to be tuned in such a way that the equilibrium between inactive and active integrin conformations can be readily regulated.

Supercapacitive swing adsorption of carbon dioxide.

An electrical effect, the supercapacitive swing adsorption (SSA) effect is reported, which allows for reversible adsorption and desorption of carbon dioxide by capacitive charge and discharge of electrically conducting porous carbon materials. The SSA effect can be observed when an electrically conducting, nanoporous carbon material is brought into contact with carbon dioxide gas and an aqueous electrolyte. Charging the supercapacitor electrodes initiates the spontaneous organization of electrolyte ions into an electric double layer at the surface of each porous electrode. The presence of this double layer leads to reversible, selective uptake and release of the CO2 as the supercapacitor is charged and discharged.

High-entropy alloy screening for halide perovskites.

As the concept of high-entropy alloying (HEA) extends beyond metals, new materials screening methods are needed. Halide perovskites (HP) are a prime case study because greater stability is needed for photovoltaics applications, and there are 322 experimentally observed HP end-members, which leads to more than 1057 potential alloys. We screen HEAHP by first calculating the configurational entropy of 106 equimolar alloys with experimentally observed end-members. To estimate enthalpy at low computational cost, we turn to the delta-lattice parameter approach, a well-known method for predicting III-V alloy miscibility. To generalize the approach for non-cubic crystals, we introduce the parameter of unit cell volume coefficient of variation (UCV), which does a good job of predicting the experimental HP miscibility data. We use plots of entropy stabilization versus UCV to screen promising alloys and identify 102 HEAHP of interest.

Formation of ionic complexes in cryogenic matrices: a case study using co-deposition of Cu- with rare gas cations in solid argon.

Matrix isolation spectra have been obtained for ionic species formed from a beam of mass-selected ions, with a coincident beam of externally generated counter-ions used to provide charge balance. Infrared spectra were obtained for copper carbonyl complexes formed following deposition of Cu(-) ions with rare-gas counter-cations into CO-doped argon matrices. Both anionic and neutral copper carbonyl complexes Cu(CO)(n)(q) (n = 1-3; q = 0, -1) were observed in the spectra, with peak positions corresponding to previously reported assignments; new partially resolved bands appearing in the range 1830-1845 cm(-1) are assigned to larger [Cu(CO)3●(CO)n](-) aggregates, having additional CO ligands in the second solvation shell. The experimental geometry ensures that all Cu-centers initially arrive at the matrix as anions, so the relative abundance of anionic relative to neutral complexes is much higher than in previous studies employing alternative methods for ion deposition; this allows for monitoring of electron-transfer processes between anions and cations in the matrix. Comparison of time-dependent vs. temperature-dependent trends reveals that there are two distinct mechanisms by which the population of anionic complexes is converted into neutral complexes: short-range electron transfer between a cation-anion pair following diffusion, and long-range electron transfer involving photodetachment of an electron from the anion into the conduction band of solid argon, resulting in eventual recombination of the electron with a cation in a remote matrix site. The spectra also show a marked dependence on the deposition temperature and dopant concentration, in that 100-fold higher CO concentrations were required during deposition with the sample window at 10 K compared to that used at 20 K, in order to obtain a similar distribution of copper carbonyl complexes. Furthermore, although no carbonyl complexes are observed initially when low concentrations of CO are used at 10 K, upon warming the matrix to 15 K, the neutral di- and tricarbonyl peaks appear abruptly, which is attributed to fast diffusion of CO stimulated by the energy released upon short-range electron-transfer between Cu(-):counter-cation pairs.

NMR analysis of the alphaIIb beta3 cytoplasmic interaction suggests a mechanism for integrin regulation.

The integrin αIIbß3 is a transmembrane (TM) heterodimeric adhesion receptor that exists in equilibrium between resting and active ligand binding conformations. In resting αIIbß3, the TM and cytoplasmic domains of αIIb and ß3 form a heterodimer that constrains αIIbß3 in its resting conformation. To study the structure and dynamics of the cytoplasmic domain heterodimer, we prepared a disulfide-stabilized complex consisting of portions of the TM domains and the full cytoplasmic domains. NMR and hydrogen-deuterium exchange of this complex in micelles showed that the αIIb cytoplasmic domain is largely disordered, but it interacts with and influences the conformation of the ß3 cytoplasmic domain. The ß3 cytoplasmic domain consists of a stable proximal helix contiguous with the TM helix and two distal amphiphilic helices. To confirm the NMR structure in a membrane-like environment, we studied the ß3 cytoplasmic domain tethered to phospholipid bilayers. Hydrogen-deuterium exchange mass spectrometry, as well as circular dichroism spectroscopy, demonstrated that the ß3 cytoplasmic domain becomes more ordered and helical under these conditions, consistent with our NMR results. Further, these experiments suggest that the two distal helices associate with lipid bilayers but undergo fluctuations that would allow rapid binding of cytoplasmic proteins regulating integrin activation, such as talin and kindlin-3. Thus, these results provide a framework for understanding the kinetics and thermodynamics of protein interactions involving integrin cytoplasmic domains and suggest that such interactions act in a concerted fashion to influence integrin stalk separation and exposure of extracellular ligand binding sites.

Submicrosecond time resolution atomic force microscopy for probing nanoscale dynamics.

We propose, simulate, and experimentally validate a new mechanical detection method to analyze atomic force microscopy (AFM) cantilever motion that enables noncontact discrimination of transient events with ~100 ns temporal resolution without the need for custom AFM probes, specialized instrumentation, or expensive add-on hardware. As an example application, we use the method to screen thermally annealed poly(3-hexylthiophene):phenyl-C(61)-butyric acid methyl ester photovoltaic devices under realistic testing conditions over a technologically relevant performance window. We show that variations in device efficiency and nanoscale transient charging behavior are correlated, thereby linking local dynamics with device behavior. We anticipate that this method will find application in scanning probe experiments of dynamic local mechanical, electronic, magnetic, and biophysical phenomena.

Charge-dependent trends in structures and vibrational frequencies of [CO-Au-O2](q) (q = -1, 0, +1) complexes: evidence for cooperative interactions.

Charge-dependent trends in the structures, vibrational frequencies, and binding energies of binary [AuCO](q) and [AuO(2)](q) and ternary [O(2)AuCO](q) complexes (q = -1,0,+1), have been investigated using density functional theory calculations. Three different geometrical motifs, given descriptive names of "separated", "pre-reactive", and "long-range", are identified for the ternary complexes. For the binary systems, the general trend is that the complexes become more diffuse as the charge becomes more negative, having longer intermolecular bond distances and weaker binding energies. The trends shown by the ternary complexes are more complicated, and are different for the various geometrical motifs. However, a general trend is that there is a cooperative interaction involving both the CO and O(2) with the Au center, which becomes more pronounced as the negative charge on the complexes increases from cationic to neutral to anionic. This cooperative interaction leads to increased electron density on the O(2) moiety, as is reflected in the bond-lengths and vibrational frequencies. Furthermore, it is found that for the pre-reactive complexes, the role of the Au center is to stabilize the formation of a conjugated π-system between the CO and O(2) molecules.

Understanding opportunities and challenges with telemedicine-delivered buprenorphine during the COVID-19 pandemic.

INTRODUCTION: Opioid use disorder (OUD) is a debilitating illness that remains a serious public health issue in the United States. Use of telemedicine to deliver medications for the treatment of OUD (MOUD) was limited until the confluence of the COVID-19 and opioid addiction epidemics in spring 2020. Starting in spring 2020, the Department of Veterans Health Affairs (VHA) transitioned from in-person to mostly telemedicine-delivered OUD care to reduce COVID-19 transmission among veterans and providers. To gain a nuanced understanding of provider perspectives on MOUD care delivery using telemedicine, we conducted semi-structured interviews with VHA providers who were using telehealth to deliver MOUD care. METHODS: We conducted semi-structed Zoom interviews with VA clinicians at nine VA Medical Centers (VAMCs) in eight states. Potential study participants were identified as providers who were involved in referrals and provision of buprenorphine treatment for chronic pain and opioid addiction. Audio-recordings of all interviews were transcribed and entered into Atlas. Ti qualitative analysis software. The study team analyzed the transcripts for major themes related to tele-prescribing practices for buprenorphine. RESULTS: Twenty-three VA providers participated in the study, representing 32% of all providers invited to participate in the study. The research team identified the following four themes: (1) COVID-19 spurred a seismic shift in OUD treatment; (2) Video calls provided a rare window into veterans' lives; (3) Providers experienced numerous challenges to virtual visits; and (4) Providers wrestled with paternalism and trust. CONCLUSIONS: The pandemic accelerated the movement toward harm reduction approaches. Prior to the pandemic, stringent requirements existed for patients receiving MOUD care. Providers in this study reflected on the need for these requirements (e.g., in-person visits, toxicology screens) and how reducing this monitoring implied more trust in patients' autonomous decisions. Providers' observation that videoconferencing offered them a window into patients' lives may offer some ways to improve rapport, and research should explore how best to incorporate the additional information conveyed in virtual visits.

Computational design of a ß-peptide that targets transmembrane helices.

The design of ß-peptide foldamers targeting the transmembrane (TM) domains of complex natural membrane proteins has been a formidable challenge. A series of ß-peptides was designed to stably insert in TM orientations in phospholipid bilayers. Their secondary structures and orientation in the phospholipid bilayer was characterized using biophysical methods. Computational methods were then devised to design a ß-peptide that targeted a TM helix of the integrin α(IIb)ß(3). The designed peptide (ß-CHAMP) interacts with the isolated target TM domain of the protein and activates the intact integrin in vitro.

Isotope dependent, temperature regulated, energy repartitioning in a low-barrier, short-strong hydrogen bonded cluster.

We investigate and analyze the vibrational properties, including hydrogen/deuterium isotope effects, in a fundamental organic hydrogen bonded system using multiple experimental (infrared multiple photon dissociation and argon-tagged action spectroscopy) and computational techniques. We note a qualitative difference between the two experimental results discussed here and employ ab initio molecular dynamics simulations to explain these results. A deeper understanding of the differences between the isotopically labeled systems arises from an analysis of the simulated cluster spectroscopy and leads to a system-bath coupling interpretation. Specifically, when a few active modes, involving the shared hydrogen/deuterium stretch, are identified and labeled as "system," with all other molecular vibrational modes being identified as "bath" modes, we find critical differences in the coupling between the system modes for the shared proton and shared deuteron cases. These differences affect the energy repartitioning between these modes resulting in a complex spectral evolution as a function of temperature. Furthermore, intensity borrowing across modes that are widely distributed in the frequency domain plays an important role on the simulated spectra.