Correlated STORM-homoFRET imaging reveals highly heterogeneous membrane receptor structures.

Mapping the self-organization and spatial distribution of membrane proteins is key to understanding their function. Developing methods that can provide insight into correlations between membrane protein colocalization and interactions is challenging. We report here on a correlated stochastic optical reconstruction microscopy/homoFRET imaging approach for resolving the nanoscale distribution and oligomeric state of membrane proteins. Using live cell homoFRET imaging of carcinoembryonic antigen-related cellular adhesion molecule 1, a cell-surface receptor known to exist in a complex equilibrium between monomer and dimer/oligomer states, we revealed highly heterogeneous diffraction-limited structures on the surface of HeLa cells. Furthermore, correlated super-resolved stochastic optical reconstruction microscopy imaging showed that these structures comprised a complex mixture and spatial distribution of self-associated carcinoembryonic antigen-related cellular adhesion molecule 1 molecules. In conclusion, this correlated approach provides a compelling strategy for addressing challenging questions about the interplay between membrane protein concentration, distribution, interaction, clustering, and function.

Practical approach for optimizing off-axis telecentric digital holographic microscope design.

Digital holographic microscopy (DHM) has become an attractive imaging tool for the analysis of living cells and histological tissues. Telecentric DHM (TDHM) is a configuration of DHM that reduces the computational demands through a priori aberration corrections. However, TDHM requires a well-aligned optical pipeline to optimize its resolution and image quality (IQ), which has traditionally complicated the alignment process. Derived from optical interference functions, we offer here a set of methodologies to simplify TDHM design and alignment by determining the optimal +1-order position, which depends on the object-reference beam angle and the interference plane rotation angle. The methods are then experimentally tested and verified on a TDHM system by imaging living HeLa cells in suspension.

Quality of Life Associated with Nausea and Vomiting from Anthracycline-Based Chemotherapy: A Pooled Data Analysis from Three Prospective Trials.

BACKGROUND: There is limited work on the impact of chemotherapy-induced nausea and vomiting (CINV) on quality of life (QoL) in adriamycin-cyclophosphamide (AC)-treated patients with breast cancer. The objectives of the study were the following: (a) to confirm if symptoms of CINV led to lower QoL during AC; (b) to evaluate the pattern of changes in patients' QoL during multiple cycles of AC; and (c) to assess if the QoL in an earlier cycle affected the QoL in subsequent cycles of AC. MATERIALS AND METHODS: This is a secondary pooled data analysis that included 303 Chinese patients with breast cancer who received 1,177 cycles of adjuvant AC in three prospective antiemetic studies. QoL data were based on Functional Living Index-emesis (FLIE) scored over three to four AC cycles. CINV symptoms assessed included "no significant nausea" (NSN), "significant nausea" (SN), "no vomiting" (NoV), "vomiting" (V), and complete response (CR). RESULTS: Across all AC cycles, the mean scores for the FLIE nausea domain for patients who experienced NSN versus SN were 10.92 versus 53.92, respectively (p < .0001), with lower scores indicating better QoL; the mean scores for the FLIE vomiting domain for patients who experienced NoV versus V were 1.44 versus 19.11, respectively (p < .0001), with similar results across subsequent cycles. Analysis of the effect of the QoL in cycle 1 on the QoL of subsequent cycles revealed the following: for the nausea domain, among patients who had cycle 1 FLIE scores ≥ versus < the mean, the corresponding scores in cycle 2 were 6.87 versus 36.71 (p < .0001); whereas those for cycle 3 were 7.07 versus 36.87 (p < .0001); and those for cycle 4 were 5.92 versus 21.48 (p < .0001). Similar findings were observed for the vomiting domain. Netupitant + palonosetron- or aprepitant/olanzapine-based antiemetics had significantly better QoL outcomes. CONCLUSION: CINV had a significant impact on the QoL of patients with breast cancer treated with AC over multiple cycles. IMPLICATIONS FOR PRACTICE: In this post-hoc analysis of three prospective studies on chemotherapy-induced nausea and vomiting (CINV), quality of life (QoL) using contemporary antiemetic regimens in Chinese breast cancer patients receiving doxorubicin-cyclophosphamide (AC) was evaluated. During the first and subsequent AC cycles, QoL was significantly better for patients who did not experience vomiting or significant nausea. QoL in an earlier cycle affected the QoL in subsequent AC cycles. Furthermore, recent regimens involving olanzapine/aprepitant or netupitant-palonosetron were associated with a positive impact in QoL. Antiemetic guideline-consistent practice and higher clinician awareness of the impact of CINV on QoL can further mitigate the negative effects of CINV on QoL.

Studies on the Importance of the 7α-, and 12α- hydroxyl groups of N-Aryl-3α,7α,12α-trihydroxy-5ß-cholan-24-amides on their Antigermination Activity Against a Hypervirulent Strain of Clostridioides (Clostridium) difficile.

Chenodeoxycholic acid (CDCA) is a natural germination inhibitor for C. difficile spores. In our previous study (J. Med. Chem., 2018, 61, 6759-6778), we identified N-phenyl-3α,7α,12α-trihydroxy-5ß-cholan-24-amide as an inhibitor of C. difficile strain R20291 with an IC50 of 1.8 µM. Studies of bile salts on spore germination have shown that chenodeoxycholate, ursodeoxycholate and lithocholate are more potent inhibitors of germination compared to cholate. Given this, we created amide analogs of chenodeoxycholic, deoxycholic, lithocholic and ursodeoxycholic acids using amines identified from our previous studies. We found that chenodeoxy- and deoxycholate derivatives were active with potencies equivalent to those for cholanamides. This indicates that only 2 out of the 3 hydroxyl groups are needed for activity and that the alpha stereochemistry at position 7 is required for inhibition of spore germination.

Automated cell tracking identifies mechanically oriented cell divisions during Drosophila axis elongation.

Embryos extend their anterior-posterior (AP) axis in a conserved process known as axis elongation. Drosophila axis elongation occurs in an epithelial monolayer, the germband, and is driven by cell intercalation, cell shape changes, and oriented cell divisions at the posterior germband. Anterior germband cells also divide during axis elongation. We developed image analysis and pattern-recognition methods to track dividing cells from confocal microscopy movies in a generally applicable approach. Mesectoderm cells, forming the ventral midline, divided parallel to the AP axis, while lateral cells displayed a uniform distribution of division orientations. Mesectoderm cells did not intercalate and sustained increased AP strain before cell division. After division, mesectoderm cell density increased along the AP axis, thus relieving strain. We used laser ablation to isolate mesectoderm cells from the influence of other tissues. Uncoupling the mesectoderm from intercalating cells did not affect cell division orientation. Conversely, separating the mesectoderm from the anterior and posterior poles of the embryo resulted in uniformly oriented divisions. Our data suggest that mesectoderm cells align their division angle to reduce strain caused by mechanical forces along the AP axis of the embryo.

Menopausal symptoms in relationship to breast cancer-specific quality of life after adjuvant cytotoxic treatment in young breast cancer survivors.

INTRODUCTIONS: For young premenopausal breast cancer patients, adjuvant chemotherapy may cause menstrual disruptions and premature menopause, which may in turn impair their quality of life (QoL). In this study among young breast cancer survivors who have undergone adjuvant chemotherapy, the objectives were to assess post-treatment menopausal symptoms and their associated factors, and to correlate these symptoms with breast cancer-specific QoL. METHODS: The study population included premenopausal young Chinese women with early-stage breast cancer who had undergone adjuvant chemotherapy between 3 and 10 years prior to enrolling into this study. At study entry, patients' characteristics and clinical features were collected; each patient had detail menstrual history collected and each filled in MENQOL and FACT-B + 4 questionnaires. RESULTS: Two hundred eighty eligible patients were recruited. For adjuvant chemotherapy, 92% received anthracyclines and 28% received taxanes; 76% received adjuvant tamoxifen. At a median of 5.0 years from initial cancer diagnosis, 49 and 11% had become post- and peri-menopausal respectively. MENQOL at study entry revealed that physical domain score was worse in overweight/obese patients (mean scores for underweight/normal vs overweight/obese: 2.65 vs 2.97, p = 0.0162). Vasomotor domain score was worse in those who received taxanes or tamoxifen (taxane vs non-taxane: 2.91 vs. 2.35, p = 0.0140; tamoxifen vs no tamoxifen: 2.75 vs. 2.34, p = 0.0479). Sexual domain score was worse among those who had become peri/post-menopausal (peri/postmenopausal vs premenopausal: 2.82 vs. 2.29, p = 0.0229). On the other hand, patients who utilized traditional Chinese medicine had significantly worse scores for vasomotor, psychosocial and physical domains. Further, there was a significant association between MENQOL scores and FACT-B + 4 scores; less severe symptoms in the MENQOL domains were associated with better QoL scores in FACT-B + 4 physical, functional, psychosocial and emotional well-being, Breast Cancer Subscale, Arm Subscale and FACT-B total score. CONCLUSION: Among premenopausal breast cancer women who had undergone adjuvant chemotherapy, those who had received taxanes or tamoxifen, were overweight/obese and utilized traditional Chinese medicine had more severe menopausal symptoms. Patients who experienced worse menopausal symptoms were found to have worse breast cancer-specific QoL. Interventional studies with an aim to alleviate menopausal symptoms are warranted to assess if overall QoL of these patients could be improved. TRIAL REGISTRATION: Not applicable.

mTOR complex 1 controls the nuclear localization and function of glycogen synthase kinase 3ß.

Glycogen synthase kinase 3ß (GSK3ß) phosphorylates and thereby regulates a wide range of protein substrates involved in diverse cellular functions. Some GSK3ß substrates, such as c-Myc and Snail, are nuclear transcription factors, suggesting the possibility that GSK3ß function is controlled through its nuclear localization. Here, using ARPE-19 and MDA-MB-231 human cell lines, we found that inhibition of mTOR complex 1 (mTORC1) leads to partial redistribution of GSK3ß from the cytosol to the nucleus and to a GSK3ß-dependent reduction of the levels of both c-Myc and Snail. mTORC1 is known to be controlled by metabolic cues, such as by AMP-activated protein kinase (AMPK) or amino acid abundance, and we observed here that AMPK activation or amino acid deprivation promotes GSK3ß nuclear localization in an mTORC1-dependent manner. GSK3ß was detected on several distinct endomembrane compartments, including lysosomes. Consistently, disruption of late endosomes/lysosomes through a perturbation of RAS oncogene family member 7 (Rab7) resulted in loss of GSK3ß from lysosomes and in enhanced GSK3ß nuclear localization as well as GSK3ß-dependent reduction of c-Myc levels. These findings indicate that the nuclear localization and function of GSK3ß is suppressed by mTORC1 and suggest a link between metabolic conditions sensed by mTORC1 and GSK3ß-dependent regulation of transcriptional networks controlling cellular biomass production.

Rab7 palmitoylation is required for efficient endosome-to-TGN trafficking.

Retromer is a multimeric protein complex that mediates endosome-to-trans-Golgi network (TGN) and endosome-to-plasma membrane trafficking of integral membrane proteins. Dysfunction of this complex has been linked to Alzheimer's disease and Parkinson's disease. The recruitment of retromer to endosomes is regulated by Rab7 (also known as RAB7A) to coordinate endosome-to-TGN trafficking of cargo receptor complexes. Rab7 is also required for the degradation of internalized integral membrane proteins, such as the epidermal growth factor receptor (EGFR). We found that Rab7 is palmitoylated and that this modification is not required for membrane anchoring. Palmitoylated Rab7 colocalizes efficiently with and has a higher propensity to interact with retromer than nonpalmitoylatable Rab7. Rescue of Rab7 knockout cells by expressing wild-type Rab7 restores efficient endosome-to-TGN trafficking, while rescue with nonpalmitoylatable Rab7 does not. Interestingly, Rab7 palmitoylation does not appear to be required for the degradation of EGFR or for its interaction with its effector, Rab-interacting lysosomal protein (RILP). Overall, our results indicate that Rab7 palmitoylation is required for the spatiotemporal recruitment of retromer and efficient endosome-to-TGN trafficking of the lysosomal sorting receptors.

Lipophilicity of the Cystic Fibrosis Drug, Ivacaftor (VX-770), and Its Destabilizing Effect on the Major CF-causing Mutation: F508del.

Deletion of phenylalanine at position 508 (F508del) in cystic fibrosis transmembrane conductance regulator (CFTR) is the most common cystic fibrosis (CF)-causing mutation. Recently, ORKAMBI, a combination therapy that includes a corrector of the processing defect of F508del-CFTR (lumacaftor or VX-809) and a potentiator of channel activity (ivacaftor or VX-770), was approved for CF patients homozygous for this mutation. However, clinical studies revealed that the effect of ORKAMBI on lung function is modest and it was proposed that this modest effect relates to a negative impact of VX-770 on the stability of F508del-CFTR. In the current studies, we showed that this negative effect of VX-770 at 10 µM correlated with its inhibitory effect on VX-809-mediated correction of the interface between the second membrane spanning domain and the first nucleotide binding domain bearing F508del. Interestingly, we found that VX-770 exerted a similar negative effect on the stability of other membrane localized solute carriers (SLC26A3, SLC26A9, and SLC6A14), suggesting that this negative effect is not specific for F508del-CFTR. We determined that the relative destabilizing effect of a panel of VX-770 derivatives on F508del-CFTR correlated with their predicted lipophilicity. Polarized total internal reflection fluorescence microscopy on a supported lipid bilayer model shows that VX-770, and not its less lipophilic derivative, increased the fluidity of and reorganized the membrane. In summary, our findings show that there is a potential for nonspecific effects of VX-770 on the lipid bilayer and suggest that this effect may account for its destabilizing effect on VX-809- rescued F508del-CFTR.

Phosphatidylserine dictates the assembly and dynamics of caveolae in the plasma membrane.

Caveolae are bulb-shaped nanodomains of the plasma membrane that are enriched in cholesterol and sphingolipids. They have many physiological functions, including endocytic transport, mechanosensing, and regulation of membrane and lipid transport. Caveola formation relies on integral membrane proteins termed caveolins (Cavs) and the cavin family of peripheral proteins. Both protein families bind anionic phospholipids, but the precise roles of these lipids are unknown. Here, we studied the effects of phosphatidylserine (PtdSer), phosphatidylinositol 4-phosphate (PtdIns4P), and phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) on caveolar formation and dynamics. Using live-cell, single-particle tracking of GFP-labeled Cav1 and ultrastructural analyses, we compared the effect of PtdSer disruption or phosphoinositide depletion with caveola disassembly caused by cavin1 loss. We found that PtdSer plays a crucial role in both caveola formation and stability. Sequestration or depletion of PtdSer decreased the number of detectable Cav1-GFP puncta and the number of caveolae visualized by electron microscopy. Under PtdSer-limiting conditions, the co-localization of Cav1 and cavin1 was diminished, and cavin1 degradation was increased. Using rapamycin-recruitable phosphatases, we also found that the acute depletion of PtdIns4P and PtdIns(4,5)P2 has minimal impact on caveola assembly but results in decreased lateral confinement. Finally, we show in a model of phospholipid scrambling, a feature of apoptotic cells, that caveola stability is acutely affected by the scrambling. We conclude that the predominant plasmalemmal anionic lipid PtdSer is essential for proper Cav clustering, caveola formation, and caveola dynamics and that membrane scrambling can perturb caveolar stability.

Cardiolipin synthesizing enzymes form a complex that interacts with cardiolipin-dependent membrane organizing proteins.

The mitochondrial glycerophospholipid cardiolipin plays important roles in mitochondrial biology. Most notably, cardiolipin directly binds to mitochondrial proteins and helps assemble and stabilize mitochondrial multi-protein complexes. Despite their importance for mitochondrial health, how the proteins involved in cardiolipin biosynthesis are organized and embedded in mitochondrial membranes has not been investigated in detail. Here we show that human PGS1 and CLS1 are constituents of large protein complexes. We show that PGS1 forms oligomers and associates with CLS1 and PTPMT1. Using super-resolution microscopy, we observed well-organized nanoscale structures formed by PGS1. Together with the observation that cardiolipin and CLS1 are not required for PGS1 to assemble in the complex we predict the presence of a PGS1-centered cardiolipin-synthesizing scaffold within the mitochondrial inner membrane. Using an unbiased proteomic approach we found that PGS1 and CLS1 interact with multiple cardiolipin-binding mitochondrial membrane proteins, including prohibitins, stomatin-like protein 2 and the MICOS components MIC60 and MIC19. We further mapped the protein-protein interaction sites between PGS1 and itself, CLS1, MIC60 and PHB. Overall, this study provides evidence for the presence of a cardiolipin synthesis structure that transiently interacts with cardiolipin-dependent protein complexes.

Structural templating of J-aggregates: Visualizing bis(monoacylglycero)phosphate domains in live cells.

Identifying the key structural and dynamical determinants that drive the association of biomolecules, whether in solution, or perhaps more importantly in a membrane environment, has critical implications for our understanding of cellular dynamics, processes, and signaling. With recent advances in high-resolution imaging techniques, from the development of new molecular labels to technical advances in imaging methodologies and platforms, researchers are now reaping the benefits of being able to directly characterize and quantify local dynamics, structures, and conformations in live cells and tissues. These capabilities are providing unique insights into association stoichiometries, interactions, and structures on sub-micron length scales. We previously examined the role of lipid headgroup chemistry and phase state in guiding the formation of pseudoisocyanine (PIC) dye J-aggregates on supported planar bilayers [Langmuir, 25, 10719]. We describe here how these same J-aggregates can report on the in situ formation of organellar membrane domains in live cells. Live cell hyperspectral confocal microscopy using GFP-conjugated GTPase markers of early (Rab5) and late (Rab7) endosomes revealed that the PIC J-aggregates were confined to domains on either the limiting membrane or intralumenal vesicles (ILV) of late endosomes, known to be enriched in the anionic lipid bis(monoacylglycero)phosphate (BMP). Correlated confocal fluorescence - atomic force microscopy performed on endosomal membrane-mimetic supported planar lipid bilayers confirmed BMP-specific templating of the PIC J-aggregates. These data provide strong evidence for the formation of BMP-rich lipid domains during multivesicular body formation and portend the application of structured dye aggregates as markers of cellular membrane domain structure, size, and formation.

Profiles of lipids, blood pressure and weight changes among premenopausal Chinese breast cancer patients after adjuvant chemotherapy.

BACKGROUND: Adjuvant chemotherapy improves outcome of patients with early breast cancer. However, chemotherapy may be associated with long term toxicities. In this retrospective cohort study, the objectives were to determine body weight, body mass index (BMI), blood pressure and fasting lipids levels of young premenopausal Chinese breast cancer patients after adjuvant chemotherapy. Potential factors associated with these parameters were identified. METHODS: Eligibility criteria include premenopausal Chinese patients who were diagnosed to have stage I-III breast cancer within 3-10 years, age < 45 and having received adjuvant chemotherapy at the time of breast cancer diagnosis. Information at initial breast cancer diagnosis were retrieved from patients' medical records and include age at diagnosis, tumor characteristics, anti-cancer treatments, blood pressure and body weight and height. At study entry, all patients had additional background demographics collected, as well as blood pressure, body weight and fasting serum lipid profiles measured. Incidence of chemotherapy-related amenorrhoea (CRA) and menopause were determined. Factors associated with weight gain, hypertension and dyslipidaemias were analyzed. RESULTS: Two hundred and eighty patients were studied. The median age at breast cancer diagnosis was 41 years (range: 24-45). The median time from breast cancer diagnosis to study entry was 5.0 years. The median age at study entry was 46.5 years (range: 28-54). 91.1% developed CRA; 48.9% had become menopausal and 10% were peri-menopausal. Between initial breast cancer diagnosis and the time of study entry, the median weight gain was 1.8 kg; 63.2% gained weight by >2%; 52.1% were overweight/obese; 30.7% had hypertension. Abnormal total-cholesterol and LDL-cholesterol occurred in 34.3% and 56.1% respectively. On multivariate analyses, older age was associated with reduced risk while occurrence of CRA and having received taxane-containing regimens were associated with increased risk of weight gain. Oestrogen-receptor positivity was associated with reduced risk while overweight/obese statuses were associated with increased risk of hypertension. Use of tamoxifen was associated with reduced risk of abnormal LDL-cholesterol. Weight gain, overweight/obese, older age, progression to post/peri-menopausal status at study entry, having received corticosteroid premedication before adjuvant chemotherapy and having received taxane-containing adjuvant chemotherapy were associated with increased risk of dyslipidaemias. CONCLUSION: Among young premenopausal Chinese breast cancer patients who had received adjuvant chemotherapy, the current study has revealed that although there was only a median weight gain of 1.8 kg, there was a nearly 60% increase in abnormal BMI. Further, a significant proportion of patients were detected to have hypertension and dyslipidaemias. Interventional studies with lifestyle modifications are warranted.

The mechanism of membrane disruption by cytotoxic amyloid oligomers formed by prion protein(106-126) is dependent on bilayer composition.

The formation of fibrillar aggregates has long been associated with neurodegenerative disorders such as Alzheimer and Parkinson diseases. Although fibrils are still considered important to the pathology of these disorders, it is now widely understood that smaller amyloid oligomers are the toxic entities along the misfolding pathway. One characteristic shared by the majority of amyloid oligomers is the ability to disrupt membranes, a commonality proposed to be responsible for their toxicity, although the mechanisms linking this to cell death are poorly understood. Here, we describe the physical basis for the cytotoxicity of oligomers formed by the prion protein (PrP)-derived amyloid peptide PrP(106-126). We show that oligomers of this peptide kill several mammalian cells lines, as well as mouse cerebellar organotypic cultures, and we also show that they exhibit antimicrobial activity. Physical perturbation of model membranes mimicking bacterial or mammalian cells was investigated using atomic force microscopy, polarized total internal reflection fluorescence microscopy, and NMR spectroscopy. Disruption of anionic membranes proceeds through a carpet or detergent model as proposed for other antimicrobial peptides. By contrast, when added to zwitterionic membranes containing cholesterol-rich ordered domains, PrP(106-126) oligomers induce a loss of domain separation and decreased membrane disorder. Loss of raft-like domains may lead to activation of apoptotic pathways, resulting in cell death. This work sheds new light on the physical mechanisms of amyloid cytotoxicity and is the first to clearly show membrane type-specific modes of action for a cytotoxic peptide.

Indolicidin binding induces thinning of a lipid bilayer.

We use all-atom molecular dynamics simulations on a massive scale to compute the standard binding free energy of the 13-residue antimicrobial peptide indolicidin to a lipid bilayer. The analysis of statistical convergence reveals systematic sampling errors that correlate with reorganization of the bilayer on the microsecond timescale and persist throughout a total of 1.4 ms of sampling. Consistent with experimental observations, indolicidin induces membrane thinning, although the simulations significantly overestimate the lipophilicity of the peptide.

Binding of TDP-43 to the 3'UTR of its cognate mRNA enhances its solubility.

TAR DNA binding protein of 43 kDa (TDP-43) has been implicated in the pathogenesis of a broad range of neurodegenerative diseases termed TDP-43 proteinopathies, which encompass a spectrum of diseases ranging from amyotrophic lateral sclerosis to frontotemporal dementia. Pathologically misfolded and aggregated forms of TDP-43 are found in cytoplasmic inclusion bodies of affected neurons in these diseases. The mechanism by which TDP-43 misfolding causes disease is not well-understood. Current hypotheses postulate that the TDP-43 aggregation process plays a major role in pathogenesis. We amplify that hypothesis and suggest that binding of cognate ligands to TDP-43 can stabilize the native functional state of the protein and ameliorate aggregation. We expressed recombinant TDP-43 containing an N-terminal Venus yellow fluorescent protein tag in Escherichia coli and induced its aggregation by altering solvent salt concentrations and examined the extent to which various oligonucleotide molecules affect its aggregation in vitro using aggregation-induced turbidity assays. We show that vYFP-TDP-43 binding to its naturally occurring RNA target that comprises a sequence on the 3'UTR region of its mRNA improves its solubility, suggesting interplay among TDP-43 solubility, oligonucleotide binding, and TDP-43 autoregulation.

Inside-out signaling promotes dynamic changes in the carcinoembryonic antigen-related cellular adhesion molecule 1 (CEACAM1) oligomeric state to control its cell adhesion properties.

Cell-cell contacts are fundamental to multicellular organisms and are subject to exquisite levels of control. The carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) can engage in both cis-homophilic (parallel) oligomerization and trans-homophilic (anti-parallel) binding. In this study, we establish that the CEACAM1 transmembrane domain has a propensity to form cis-dimers via the transmembrane-embedded (432)GXXXG(436) motif and that this basal state is overcome when activated calmodulin binds to the CEACAM1 cytoplasmic domain. Although mutation of the (432)GXXXG(436) motif reduced CEACAM1 oligomerization, it did not affect surface localization of the receptor or influence CEACAM1-dependent cellular invasion by the pathogenic Neisseria. The mutation did, however, have a striking effect on CEACAM1-dependent cellular aggregation, increasing both the kinetics of cell-cell association and the size of cellular aggregates formed. CEACAM1 association with tyrosine kinase c-Src and tyrosine phosphatases SHP-1 and SHP-2 was not affected by the (432)GXXXG(436) mutation, consistent with their association with the monomeric form of wild type CEACAM1. Collectively, our results establish that a dynamic oligomer-to-monomer shift in surface-expressed CEACAM1 facilitates trans-homophilic binding and downstream effector signaling.

Super-resolved FT-IR spectroscopy: Strategies, challenges, and opportunities for membrane biophysics.

Direct correlation of molecular conformation with local structure is critical to studies of protein- and peptide-membrane interactions, particularly in the context of membrane-facilitated aggregation, and disruption or disordering. Infrared spectroscopy has long been a mainstay for determining molecular conformation, following folding dynamics, and characterizing reactions. While tremendous advances have been made in improving the spectral and temporal resolution of infrared spectroscopy, it has only been with the introduction of scanned-probe techniques that exploit the raster-scanning tip as either a source, scattering tool, or measurement probe that researchers have been able to obtain sub-diffraction limit IR spectra. This review will examine the history of correlated scanned-probe IR spectroscopies, from their inception to their use in studies of molecular aggregates, membrane domains, and cellular structures. The challenges and opportunities that these platforms present for examining dynamic phenomena will be discussed. This article is part of a Special Issue entitled: FTIR in membrane proteins and peptide studies.

The sticholysin family of pore-forming toxins induces the mixing of lipids in membrane domains.

Sticholysins (Sts) I and II (StI/II) are pore-forming toxins (PFTs) produced by the Caribbean Sea anemone Stichodactyla helianthus belonging to the actinoporin family, a unique class of eukaryotic PFTs exclusively found in sea anemones. The role of lipid phase co-existence in the mechanism of the action of membranolytic proteins and peptides is not clearly understood. As for actinoporins, it has been proposed that phase separation promotes pore forming activity. However little is known about the effect of sticholysins on the phase separation of lipids in membranes. To gain insight into the mechanism of action of sticholysins, we evaluated the effect of these proteins on lipid segregation using differential scanning calorimetry (DSC) and atomic force microscopy (AFM). New evidence was obtained reflecting that these proteins reduce line tension in the membrane by promoting lipid mixing. In terms of the relevance for the mechanism of action of actinoporins, we hypothesize that expanding lipid disordered phases into lipid ordered phases decreases the lipid packing at the borders of the lipid raft, turning it into a more suitable environment for N-terminal insertion and pore formation.