Surface Anchorage Research Articles

Fullerene C60: Dielectric and elastic properties of E8 nematic liquid crystal

This study presents a comprehensive analysis of the impact of Fullerene C60 doping on the dielectric and elastic behavior of E8 coded nematic liquid crystals. By investigating the underlying mechanisms, we unveil how Fullerene C60 can effectively modify the properties of nematic liquid crystals, particularly their dielectric and elastic characteristics. Through the analysis of Cole-Cole plots and semicircle plots, we gain valuable insights into the suitability of an equivalent electronic circuit model, thereby holding promise for liquid crystal-based devices with improved performance and functionality in electrical circuit applications. Furthermore, our results demonstrate that the presence of Fullerene C60 induces higher splay elastic constant (K11) values in doped nematic liquid crystals, attributed to an increase in the sample's threshold voltage. Moreover, the presence of Fullerene C60 fosters strong elastic interactions in the liquid crystal system due to surface anchorage, resulting in an elevation of its elastic energy.

Surface forces and friction between Langmuir-Blodgett polymer layers in a nonpolar solvent

Optimization of boundary lubrication by tuning the confined molecular structures formed by surface-active additives such as surfactants and polymers is of key importance to improving energy efficiency in mechanical processes. Here, using the surface forces apparatus (SFA), we have directly measured the normal and shear forces between surface layers of a functionalised olefin copolymer (FOCP) in n-dodecane, deposited onto mica using the Langmuir-Blodgett (LB) technique. The FOCP has an olefin backbone decorated with a statistical distribution of polar-aromatic groups, with a structure that we term as “centipede”. The effect of lateral confinement, characterised by the surface pressure, Πdep, at the air–water interface at which the LB films are transferred, was examined. Normal force profiles revealed that the thickness of the LB films increased significantly with Πdep, with the film thickness (t > 20 nm) inferring a multi-layered film structure, consistent with the interfacial characterisation results from synchrotron X-ray reflectivity (XRR) measurements. The coefficient of friction, µ, between the LB films spanned two orders of magnitude from superlubricity (µ ∼ 0.002) to much higher friction (µ > 0.1) depending nonlinearly on Πdep, with the lowest friction observed at the intermediate Πdep. Molecular arrangement upon LB compression leads to the multilayer film with a structure akin to an interfacial gel, with transient crosslinking facilitated by the intra- and inter-molecular interactions between the functional groups. We attribute the differences in frictional behaviour to the different prevalence of the FOCP functional groups at the lubricating interface, which depends sensitively on the degree of compression at the air–water interface prior to the LB deposition. The LB films remain intact after repeated compression (up to pressures of 10 MPa) and shear cycles, indicating strong surface anchorage and structural robustness as a load-bearing and shear-mediating boundary layer. These unprecedented results from the friction measurements between LB films of a statistical copolymer in oil point towards new strategies for tailoring macromolecular architecture for mediating efficient energy dissipation in oil-based tribological applications.

Response of Osteoblasts on Amine-Based Nanocoatings Correlates with the Amino Group Density.

Increased life expectancy in industrialized countries is causing an increased incidence of osteoporosis and the need for bioactive bone implants. The integration of implants can be improved physically, but mainly by chemical modifications of the material surface. It was recognized that amino-group-containing coatings improved cell attachment and intracellular signaling. The aim of this study was to determine the role of the amino group density in this positive cell behavior by developing controlled amino-rich nanolayers. This work used covalent grafting of polymer-based nanocoatings with different amino group densities. Titanium coated with the positively-charged trimethoxysilylpropyl modified poly(ethyleneimine) (Ti-TMS-PEI), which mostly improved cell area after 30 min, possessed the highest amino group density with an N/C of 32%. Interestingly, changes in adhesion-related genes on Ti-TMS-PEI could be seen after 4 h. The mRNA microarray data showed a premature transition of the MG-63 cells into the beginning differentiation phase after 24 h indicating Ti-TMS-PEI as a supportive factor for osseointegration. This amino-rich nanolayer also induced higher bovine serum albumin protein adsorption and caused the cells to migrate slower on the surface after a more extended period of cell settlement as an indication of a better surface anchorage. In conclusion, the cell spreading on amine-based nanocoatings correlated well with the amino group density (N/C).

Type B CTD Proteins Secreted by the Type IX Secretion System Associate with PorP-like Proteins for Cell Surface Anchorage

The Bacteroidetes type IX secretion system (T9SS) consists of at least 20 components that translocate proteins with type A or type B C-terminal domain (CTD) signals across the outer membrane (OM). While type A CTD proteins are anchored to the cell surface via covalent linkage to the anionic lipopolysaccharide, it is still unclear how type B CTD proteins are anchored to the cell surface. Moreover, very little is known about the PorE and PorP components of the T9SS. In this study, for the first time, we identified a complex comprising the OM β-barrel protein PorP, the OM-associated periplasmic protein PorE and the type B CTD protein PG1035. Cross-linking studies supported direct interactions between PorE-PorP and PorP-PG1035. Furthermore, we show that the formation of the PorE-PorP-PG1035 complex was independent of PorU and PorV. Additionally, the Flavobacterium johnsoniae PorP-like protein, SprF, was found bound to the major gliding motility adhesin, SprB, which is also a type B CTD protein. Together, these results suggest that type B-CTD proteins may anchor to the cell surface by binding to their respective PorP-like proteins.

Controlling exsolution with a charge-balanced doping approach

While exsolution is widely observed among perovskite hosts as an attractive technique for in-situ catalyst synthesis, our current understanding of the complex exsolution-host relationships is solely based on the conventional approach of using a small amount of a single dopant at a limited high-temperature range (≥ 800 °C). Herein, we develop a charge-balanced double-doping approach that opens new doors for the synthesis of a wide range of compositions, and the highly tunable nature of these compositions provides a basis for controlling exsolved particle size, distribution, composition, and surface anchorage. Against the conventional wisdom that high doping level leads to unstable exsolution, we show that increased double-doping levels, enabled by our novel method, can stabilize the perovskite phase in reducing conditions to provide high conductivity (> 35 S/cm) at low temperatures (450–650 °C) and exsolve smaller, more densely populated particles with different chemistry than their lightly doped analogues. Furthermore, we find that associated defects might be the main factor that determines nucleation sites, and the conductivity of the host may play a crucial role in exsolution kinetics by facilitating cation transport. This study paves the way for controlling exsolved electrocatalyst properties by engineering the charge-balanced B-site and offers new knowledge that links exsolution to defect chemistry.

Polydopamine-Based Interfacial Engineering of Extracellular Matrix Hydrogels for the Construction and Long-Term Maintenance of Living Three-Dimensional Tissues.

Diverse biological processes in the body rely on the ability of cells to exert contractile forces on their extracellular matrix (ECM). In three-dimensional (3D) cell culture, however, this intrinsic cellular property can cause unregulated contraction of ECM hydrogel scaffolds, leading to a loss of surface anchorage and the resultant structural failure of in vitro tissue constructs. Despite advances in the 3D culture technology, this issue remains a significant challenge in the development and long-term maintenance of physiological 3D in vitro models. Here, we present a simple yet highly effective and accessible solution to this problem. We leveraged a single-step surface functionalization technique based on polydopamine to drastically increase the strength of adhesion between hydrogel scaffolds and cell culture substrates. Our method is compatible with different types of ECM and polymeric surfaces and also permits prolonged shelf storage of functionalized culture substrates. The proof-of-principle of this technique was demonstrated by the stable long-term (1 month) 3D culture of human lung fibroblasts. Furthermore, we showed the robustness and advanced application of the method by constructing a dynamic cell stretching system and performing over 100 000 cycles of mechanical loading on 3D multicellular constructs for visualization and quantitative analysis of stretch-induced tissue alignment. Finally, we demonstrated the potential of our technique for the development of microphysiological in vitro models by establishing microfluidic 3D co-culture of vascular endothelial cells and fibroblasts to engineer self-assembled, perfusable 3D microvascular beds.

Interplay between Amphiphilic Stabilizers and Cholesterol in the Stabilization of Itraconazole Nanoparticles Prepared by Flash Nanoprecipitation.

While flash nanoprecipitation (FNP) has proven to be an extremely rapid and highly efficient nanoparticle fabrication process for hydrophobic drugs, physical instability associated with nonequilibrium molecular orientation of amphiphilic stabilizers (ASs) in nanoparticles remains a major snag in the general application of this nanotechnology, particularly for a drug with ACDLog P in the range of ∼2-9. This study was aimed at elucidating the costabilizing role of cholesterol (CLT) in the FNP of AS-stabilized nanoparticles of itraconazole (ITZ), a model drug with an ACDLog P of 4.35 ± 1.22 and log P of 5.66. The presence of CLT was shown to reduce the initial particle size and markedly improve the short-term storage stability of ITZ nanoparticles. The stability-enhancement by CLT can be linked to its higher miscibility or stronger interaction with the AS hydrophobic moiety than with ITZ (as reflected by the absolute differences of their solubility parameter values). Surface analyses employing X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) suggest that, through the coprecipitation of CLT with ITZ to form a mixed hydrophobic drug core, the CLT molecules that are exposed on the core surface serve to afford a stronger and more timely surface anchorage of the AS hydrophobic moieties, thereby facilitating the rearrangement of AS molecules toward the stable micelle-like structure. The present findings offer a mechanistic insight into the interplay between amphiphilic stabilizer and costabilizer in enhancing the physical stability of drug nanoparticles and may carry important implications for the development of more stable and efficacious nanoparticle therapeutics.

Morphological and structural characterization of the attachment system in aerial roots of Syngonium podophyllum.

The attachment of aerial roots of Syngonium podophyllum involves a multi-step process adjusted by multi-scale structures. Helical-crack root hairs are first found in the attachment system, representing specialized structures for surface anchorage. The morphological variability of attachment organs reflects diverse climbing strategies. One such anchoring mode in clinging-climbers involves the time-dependent interaction between roots and the support: By naturally occurring adhesive roots with root hairs, the plant can ascend on supports of any shape and size. As a typical root-climber, Syngonium podophyllum develops elongate aerial roots at nodes. Here, we studied its attachment behavior from the external morphology to the internal structure in detail. Through SEM and LM observation on several root-substrate interfaces, we suggested that the attachment of aerial roots was mediated by a multi-step process, in which root hairs played significant roles in releasing mucilaginous substance and securing the durable anchorage. We summarized all the types of shape changes of root hairs with particular focus on the abnormal transition from a tube to a helical-crack ribbon. We demonstrated our understanding with respect to the formation of the helical-crack root hairs, based on the structural evidence of cellulose microfibrils orientation on the cell wall lamellae. The helical-crack root hairs serving as energy-dissipating units retard the failure of adhesion under high winds and loads.

Interactions of the (R) Ru-BINAP catalytic complex with an inorganic matrix in stereoselective hydrogenation of methylacetoacetate: kinetic, XPS and DRIFT studies

Stereoselective hydrogenation of methyl acetoacetate to optical isomers of methyl-3-hydroxybutanoate over various forms of supported [RuCl((R)-BINAP)(p-cymene)]Cl is reported. The catalysts were prepared via two alternative methods: direct immobilization, and surface anchorage with heteropolyacids. The kinetic data (rate constants, optical yields, overall selectivity to methyl-3-hydroxybutanoate) were discussed and interpreted with help of XPS and DRIFT to assess bonding surface interactions. In all cases montmorillonite as a model support was employed. It was shown that the stereoselective course was dependent on the mode of [RuCl((R)-BINAP)(p-cymene)]Cl immobilization. The procedure based on the commonly used impregnation did not provide a catalyst with a stable anchorage of the active complex. Strong surface anchorage was found for a catalystproduced with help of H4SiMo12O40 heteropolyacid, but due to structural changes upon the reaction the catalyst performance in the reaction was poor. When H3PW12O40 was employed, the immobilization provided a catalyst with a very good performance. The two-step immobilization via the dimer [RuCl2(p-cymene)]2 instead of the one-step with [RuCl((R)-BINAP)(p-cymene)]Cl yielded a catalyst with the performance parameters comparable to the homogeneous experiments with [RuCl((R)-BINAP)(p-cymene)]Cl dissolved in the reaction mixture. It was due to breaking up the original dimer structure and accomplishing the surface interaction through the adsorbed monomeric units.

Key diffusion mechanisms involved in regulating bidirectional water permeation across E. coli outer membrane lectin.

Capsular polysaccharides (CPSs) are major bacterial virulent determinants that facilitate host immune evasion. E. coli group1 K30CPS is noncovalently attached to bacterial surface by Wzi, a lectin. Intriguingly, structure based phylogenetic analysis indicates that Wzi falls into porin superfamily. Molecular dynamics (MD) simulations further shed light on dual role of Wzi as it also functions as a bidirectional passive water specific porin. Such a functional role of Wzi was not realized earlier, due to the occluded pore. While five water specific entry points distributed across extracellular & periplasmic faces regulate the water diffusion involving different mechanisms, a luminal hydrophobic plug governs water permeation across the channel. Coincidently, MD observed open state structure of “YQF” triad is seen in sugar-binding site of sodium-galactose cotransporters, implicating its involvement in K30CPS surface anchorage. Importance of Loop 5 (L5) in membrane insertion is yet another highlight. Change in water diffusion pattern of periplasmic substitution mutants suggests Wzi’s role in osmoregulation by aiding in K30CPS hydration, corroborating earlier functional studies. Water molecules located inside β-barrel of Wzi crystal structure further strengthens the role of Wzi in osmoregulation. Thus, interrupting water diffusion or L5 insertion may reduce bacterial virulence.

Covalent Grafting of Coordination Polymers on Surfaces: The Case of Hybrid Valence Tautomeric Interphases.

We have developed a novel approach for grafting coordination polymers, structured as nanoparticles bearing surface reactive carboxylic groups, to amino-functionalized surfaces through a simple carbodiimide-mediated coupling reaction. As a proof-of-concept to validate our approach, and on the quest for novel hybrid interphases with potential technological applications, we have used valence tautomeric nanoparticles exhibiting spin transition at or around room temperature. SEM and AFM characterization reveal that the nanoparticles were organized chiefly into a single monolayer while X-ray photoelectron spectroscopy (XPS) measurements confirm that the nanoparticles retain a temperature-induced electronic redistribution upon surface anchorage. Our results represent an effective approach towards the challenging manufacture of coordination polymers.

Immobilised chiral inducer on Pt-based mesoporous titanate nanotubes as heterogeneous catalysts for enantioselective hydrogenation

A new series of chiral porous titanate nanotubes (TNTs) containing (−)-11-trimethoxysilyl-cinchonidine (TMS-CD) moieties were synthesized via direct surface anchorage. These hybrid solids were used as supports for Pt (1wt%) catalysts and evaluated in heterogeneous enantioselective hydrogenation of 1-phenyl-1,2-propanodione. The supports and catalysts were characterized by a variety of techniques including TGA, N2 adsorption isotherms, solid state NMR (13C and 29Si), XRD, HR-TEM, DRIFTs and XPS. For the best system the hydrogen pressure, solvent effects and recycles were studied. The maximum enantiomeric excess (ee) and the turnover frequency obtained under optimized conditions with 1% Pt/TNT-CD were 37% (at 15wt% nominal content of TMS-CD) and 165min−1 (at 10wt% nominal content of TMS-CD), respectively. The variation of H2 pressure and solvent affects both the activity and enantioselectivity due to the substrate adsorption on the metal active sites. Additionally, these heterogeneous catalysts can also be easily recycled and reused for three times without the loss of activity and enantioselectivity. After the 3rd cycle, catalyst deactivation due to the leaching of Pt nanoparticles and modifier hydrogenation in the feed was detected.

In situ growth of nanoparticles through control of non-stoichiometry

Surfaces decorated with uniformly dispersed catalytically active nanoparticles play a key role in many fields, including renewable energy and catalysis. Typically, these structures are prepared by deposition techniques, but alternatively they could be made by growing the nanoparticles in situ directly from the (porous) backbone support. Here we demonstrate that growing nano-size phases from perovskites can be controlled through judicious choice of composition, particularly by tuning deviations from the ideal ABO3 stoichiometry. This non-stoichiometry facilitates a change in equilibrium position to make particle exsolution much more dynamic, enabling the preparation of compositionally diverse nanoparticles (that is, metallic, oxides or mixtures) and seems to afford unprecedented control over particle size, distribution and surface anchorage. The phenomenon is also shown to be influenced strongly by surface reorganization characteristics. The concept exemplified here may serve in the design and development of more sophisticated oxide materials with advanced functionality across a range of possible domains of application.

Phase I Clinical Trial of Autologous Ascites-derived Exosomes Combined With GM-CSF for Colorectal Cancer

Exosomes are small membrane vesicles that are secreted by a multitude of cell types. The exosomes derived from dendritic cells (Dex), tumor cells (Tex), and malignant effusions demonstrate immunomodulatory functions, and are even under clinical trial for cancer treatments. In this study we report the phase I clinical trial of the ascites-derived exosomes (Aex) in combination with the granulocyte–macrophage colony-stimulating factor (GM-CSF) in the immunotherapy of colorectal cancer (CRC). The Aex isolated by sucrose/D2O density gradient ultracentrifugation are 60–90-nm vesicles that contain the diverse immunomodulatory markers of exosomes and tumor-associated carcinoembryonic antigen (CEA). Totally 40 patients (HLA-A0201+CEA+) with advanced CRC were enrolled in the study, and randomly assigned to treatments with Aex alone or Aex plus GM-CSF. Patients in both groups received a total of four subcutaneous immunizations at weekly intervals. We found that both therapies were safe and well tolerated, and that Aex plus GM-CSF but not Aex alone can induce beneficial tumor-specific antitumor cytotoxic T lymphocyte (CTL) response. Therefore, our study suggests that the immunotherapy of CRC with Aex in combination with GM-CSF is feasible and safe, and thus can serve as an alternative choice in the immunotherapy of advanced CRC.

Role of Laminin Terminal Globular Domains in Basement Membrane Assembly

Laminins contribute to basement membrane assembly through interactions of their N- and C-terminal globular domains. To further analyze this process, recombinant laminin-111 heterotrimers with deletions and point mutations were generated by recombinant expression and evaluated for their ability to self-assemble, interact with nidogen-1 and type IV collagen, and form extracellular matrices on cultured Schwann cells by immunofluorescence and electron microscopy. Wild-type laminin and laminin without LG domains polymerized in contrast to laminins with deleted alpha1-, beta1-, or gamma1-LN domains or with duplicated beta1- or alpha1-LN domains. Laminins with a full complement of LN and LG domains accumulated on cell surfaces substantially above those lacking either LN or LG domains and formed a lamina densa. Accumulation of type IV collagen onto the cell surface was found to require laminin with separate contributions arising from the presence of laminin LN domains, nidogen-1, and the nidogen-binding site in laminin. Collectively, the data support the hypothesis that basement membrane assembly depends on laminin self-assembly through formation of alpha-, beta-, and gamma-LN domain complexes and LG-mediated cell surface anchorage. Furthermore, type IV collagen recruitment into the laminin extracellular matrices appears to be mediated through a nidogen bridge with a lesser contribution arising from a direct interaction with laminin.

Surface anchorage of superantigen SEA promotes induction of specific antitumor immune response by tumor-derived exosomes

Tumor-derived exosomes have been regarded as a new kind of cancer vaccine; however, their therapeutic efficacy needs to be further improved. Superantigen staphylococcal enterotoxin A (SEA)-coated tumor cells have been shown to potently induce tumor-specific T cell response. To increase efficacy of tumor-derived exosomes to induce antitumor immune response, we modified the exosomes by protein transfer of SEA tailed with a highly hydrophobic transmembrane domain (SEA-TM) and designated those SEA-TM-anchored exosomes as Exo/SEA-TM. We found the exosomes secreted from murine lymphoma E.G7-OVA cell line were round vesicles with the sizes of 40-100 nm limited by a bilayer membrane. Interestingly, the inner structure of the exosomes were visible under the transmission electron microscope; those "honeycomb-like" inner structure has not been described by other labs. Immunization with Exo/SEA-TM inhibited tumor growth and prolonged survival of the mice challenged with parental tumor cells more significantly than with exosomes (Exo) and even more than with the mixture of exosomes and SEA-TM. The results of mixed lymphocyte-tumor reaction (MLTR) showed that the increased IL-2, IFN-gamma secretion, and specific cytotoxic T lymphocyte (CTL) could be effectively induced from the splenic lymphocytes of the mice immunized with Exo/SEA-TM. In vivo depletion experiments showed that CD8(+) T cells are the main effector cells, and both CD4(+) T cells and NK cells are also involved in the antitumor effect of Exo/SEA-TM immunization. Therefore, tumor-derived exosomes surface anchored with SEA-TM can efficiently induce tumor-specific CTL thereby resulting in more potent inhibition of tumor growth. Our data provide an efficient and novel approach to tumor immunotherapy by protein modification of tumor-derived exosomes.

PavA ofStreptococcus pneumoniaeModulates Adherence, Invasion, and Meningeal Inflammation

Pneumococcal adherence and virulence factor A (PavA) is displayed to the cell outer surface of Streptococcus pneumoniae and mediates pneumococcal binding to immobilized fibronectin. PavA, which lacks a typical gram-positive signal sequence and cell surface anchorage motif, is essential for pneumococcal virulence in a mouse infection model of septicemia. In this report the impact of PavA on pneumococcal adhesion to and invasion of eukaryotic cells and on experimental pneumococcal meningitis was investigated. In the experimental mouse meningitis model, the virulence of the pavA knockout mutant of S. pneumoniae D39, which did not show alterations of subcellular structures as indicated by electron microscopic studies, was strongly decreased. Pneumococcal strains deficient in PavA showed substantially reduced adherence to and internalization of epithelial cell lines A549 and HEp-2. Similar results were obtained with human brain-derived microvascular endothelial cells and human umbilical vein-derived endothelial cells. Attachment and internalization of pneumococci were not significantly affected by preincubation or cocultivations of pneumococci with anti-PavA antisera. Pneumococcal adherence was also not significantly affected by the addition of PavA protein. Complementation of the pavA knockout strain with exogenously added PavA polypeptide did not restore adherence of the mutant. These data suggest that PavA affects pneumococcal colonization by modulating expression or function of important virulence determinants of S. pneumoniae.

Cell adhesive PET membranes by surface grafting of RGD peptidomimetics

A non-peptide mimic of the Arg-Gly Asp (RGD) active sequence of adhesive proteins (such as vitronectin) has been equipped with two different spacer-arms for surface anchorage. The covalent grafting on poly(ethylene terephthalate) (PET) membrane was realized via the activation of the hydroxyl polymer chain-ends by tosylation followed by nucleophilic substitution. The surface density of peptidomimetics was determined by X-ray photoelectron spectroscopy (XPS), on the basis of F/C atomic ratios since a fluorine tag was incorporated into the RGD-like compounds. The biological activity of soluble peptidomimetics was evaluated versus isolated human integrin α v β 3 (vitronectin receptor), and versus CaCo2 cells. Inhibition of cellular adhesion was observed after pre-incubation of CaCo2 cells with soluble peptidomimetics. On the other hand a significant promotion of cellular adhesion resulted from the surface grafting of peptidomimetics on the PET culture substrate. The best performance was obtained with the RGD-like integrin ligand bearing a triethylene glycol spacer-arm.

Posttranslational modifications required for cell surface localization and function of the fungal adhesin Aga1p.

Adherence of fungal cells to host substrates and each other affects their access to nutrients, sexual conjugation, and survival in hosts. Adhesins are cell surface proteins that mediate these different cell adhesion interactions. In this study, we examine the in vivo functional requirements for specific posttranslational modifications to these proteins, including glycophosphatidylinositol (GPI) anchor addition and O-linked glycosylation. The processing of some fungal GPI anchors, creating links to cell wall beta-1,6 glucans, is postulated to facilitate postsecretory traffic of proteins to cell wall domains conducive to their functions. By studying the yeast sexual adhesin subunit Aga1p, we found that deletion of its signal sequence for GPI addition eliminated its activity, while deletions of different internal domains had various effects on function. Substitution of the Aga1p GPI signal domain with those of other GPI-anchored proteins, a single transmembrane domain, or a cysteine capable of forming a disulfide all produced functional adhesins. A portion of the cellular pool of Aga1p was determined to be cell wall resident. Aga1p and the alpha-agglutinin Agalpha1p were shown to be under glycosylated in cells lacking the protein mannosyltransferase genes PMT1 and PMT2, with phenotypes manifested only in MATalpha cells for single mutants but in both cell types when both genes are absent. We conclude that posttranslational modifications to Aga1p are necessary for its biogenesis and activity. Our studies also suggest that in addition to GPI-glucan linkages, other cell surface anchorage mechanisms, such as transmembrane domains or disulfides, may be employed by fungal species to localize adhesins.

Interactions of a hemidesmosome component and actinin family members.

Hemidesmosomes are multimeric protein complexes that attach epithelial cells to their underlying matrix and serve as cell surface anchorage sites for the keratin cytoskeleton. Two hemidesmosome components, the alpha6beta4 integrin heterodimer and a human autoantigen termed BP180, are transmembrane proteins that link the extracellular matrix to the keratin network in cells. Here, we report that actinin-4, an actin-bundling protein, is a potential binding partner for BP180. Using yeast two-hybrid, we have mapped the binding site for BP180 to the C-terminal region of actinin-4. This site contains two EF-hand, Ca2+ regulation domains and shares 87% sequence homology with the same region in actinin-1. Consistent with this, BP180 can bind actinin-1 in both the yeast two-hybrid assay and in immunoprecipitation assays. To determine whether the EF-hand domain is a consensus binding sequence for BP180, we tested whether other proteins with this domain bind BP180. None of the proteins tested including calmodulin, with 4 EF-hand domains, and myosin regulatory light chain, with 1 EF-hand domain, interacts with BP180 in yeast two-hybrid system and immunoprecipitation studies, suggesting that the interaction between BP180 and actinin family members is specific. We have compared the distribution of actinin-1 and actinin-4 with that of BP180 in MCF-10A and pp126 cells. Surprisingly, BP180 localizes not only to sites of cell-substratum interaction, but is also present at sites of cell-cell contacts where it co-distributes with both actinin-1 and actinin-4 as well as other adherens junction proteins. In oral tissues, BP180 is present along the basement membrane and at cell-cell contact sites in basal epithelial cells where it co-distributes with adherens junction proteins. Since BP180 antibodies inhibit association of junction proteins at sites of cell-cell contact in oral keratinocytes, these results suggest that BP180 may play a role in establishing cell-cell interactions. We discuss a role for BP180 in crosstalk between cell-matrix and cell-cell junctions.