Superdomains in the protein structure hierarchy: The case of PTP-C2.

Superdomain is uniquely defined in this work as a conserved combination of different globular domains in different proteins. The amino acid sequences of 25 structurally and functionally diverse proteins from fungi, plants, and animals have been analyzed in a test of the superdomain hypothesis. Each of the proteins contains a protein tyrosine phosphatase (PTP) domain followed by a C2 domain. Four novel conserved sequence motifs have been identified, one in the PTP domain and three in the C2 domain. All contribute to the PTP-C2 domain interface in PTEN, a tumor suppressor, and all are more conserved than the PTP signature motif, HCX3 (K/R)XR, in the 25 sequences. We show that PTP-C2 was formed prior to the fungi, plant, and animal kingdom divergence. A superdomain as defined here does not fit the usual protein structure classification system. The demonstrated existence of one superdomain suggests the existence of others.

Branched polymer models and the mechanism of multilayer film buildup.

The "in and out diffusion" hypothesis does not provide a conclusive explanation of the buildup displayed by some polyelectrolyte multilayer film systems. Here, we report initial tests of an alternative hypothesis, on which the completion of each adsorption cycle results in an increase in the number of polymer binding sites on the film surface. Polycationic dendrimeric peptides, which can potentially bind several oppositely-charged peptides each, have been designed, synthesized and utilized in comparative film buildup experiments. Material deposited, internal film structure and film surface morphology have been studied by ultraviolet spectroscopy (UVS), circular dichroism spectroscopy (CD), quartz crystal microbalance (QCM) and atomic force microscopy (AFM). Polycations tended to contribute more to film buildup than did polyanions on quartz but not on gold. Increasing the number of branches in the dendrimeric peptides from 4 to 8 reproducibly resulted in an increase in the film growth rate on quartz but not on gold. Peptide backbones tended to adopt a ß-strand conformation on incorporation into a film. Thicker films had a greater surface roughness than thin films. The data are consistent with film buildup models in which the average number of polymer binding sites will increase with each successive adsorption cycle in the range where exponential growth is displayed.

Four-dimensional motility tracking of biological cells by digital holographic microscopy.

Three-dimensional profiling and tracking by digital holography microscopy (DHM) provide label-free and quantitative analysis of the characteristics and dynamic processes of objects, since DHM can record real-time data for microscale objects and produce a single hologram containing all the information about their three-dimensional structures. Here, we have utilized DHM to visualize suspended microspheres and microfibers in three dimensions, and record the four-dimensional trajectories of free-swimming cells in the absence of mechanical focus adjustment. The displacement of microfibers due to interactions with cells in three spatial dimensions has been measured as a function of time at subsecond and micrometer levels in a direct and straightforward manner. It has thus been shown that DHM is a highly efficient and versatile means for quantitative tracking and analysis of cell motility.

Molecular physiology of the tensin brotherhood of integrin adaptor proteins.

Numerous proteins have been identified as constituents of the adhesome, the totality of molecular components in the supramolecular assemblies known as focal adhesions, fibrillar adhesions and other kinds of adhesive contact. The transmembrane receptor proteins called integrins are pivotal adhesome members, providing a physical link between the extracellular matrix (ECM) and the actin cytoskeleton. Tensins are ever more widely investigated intracellular adhesome constituents. Involved in cell attachment and migration, cytoskeleton reorganization, signal transduction and other processes relevant to cancer research, tensins have recently been linked to functional properties of deleted in liver cancer 1 (DLC1) and a mitogen-activated protein kinases (MAPK), to cell migration in breast cancer, and to metastasis suppression in the kidney. Tensins are close relatives of phosphatase homolog/tensin homolog (PTEN), an extensively studied tumor suppressor. Such findings are recasting the earlier vision of tensin (TNS) as an actin-filament (F-actin) capping protein in a different light. This critical review aims to summarize current knowledge on tensins and thus to highlight key points concerning the expression, structure, function, and evolution of the various members of the TNS brotherhood. Insight is sought by comparisons with homologous proteins. Some historical points are added for perspective.

Protein- and peptide-based electrospun nanofibers in medical biomaterials.

Electrospun fibers are being studied and developed because they hold considerable promise for realizing some advantages of nanostructured materials. The fibers can be made of biocompatible and biodegradable polymers. Electrospinning has therefore attracted interest in biotechnology and medicine, and there has been rapid growth in this area in recent years. This review presents an introduction to polymer nanofiber electrospinning, focusing on the use of natural proteins and synthetic peptides. We summarize key physical properties of protein-based and peptide-based nanofiber mats, survey biomedical applications of these materials, identify key challenges, and outline future prospects for development of the technology for tissue engineering, drug delivery, wound healing, and biosensors. FROM THE CLINICAL EDITOR: This review focuses on polymer nanofiber electrospinning using natural proteins and synthetic peptides. The authors describe key properties and applications of these materials, and outline future prospects for tissue engineering, drug delivery, wound healing, and biosensors based on these nanomats and nanofibers.

Measurement of the traction force of biological cells by digital holography.

The traction force produced by biological cells has been visualized as distortions in flexible substrata. We have utilized quantitative phase microscopy by digital holography (DH-QPM) to study the wrinkling of a silicone rubber film by motile fibroblasts. Surface deformation and the cellular traction force have been measured from phase profiles in a direct and straightforward manner. DH-QPM is shown to provide highly efficient and versatile means for quantitatively analyzing cellular motility.

A synthetic polypeptide electrospun biomaterial.

Fiber mats of a synthetic anionic copolypeptide of l-glutamic acid and l-tyrosine (PLEY) have been produced by electrospinning, and physical, chemical, and biological properties of the fibers have been characterized in vitro. Fibers were obtained from polymer dissolved in water at concentrations of 20-60% (w/v) but not below this range. Applied voltage and spinneret-collector distance were also found to influence polymer spinnability. Oriented fibers were obtained by changing the geometry of the collector. Fiber diameter was measured by scanning electron microscopy (SEM). A common chemical reagent was used to cross-link polymers postspinning. Fiber solubility in aqueous solution varied as a function of cross-linking time. Cationic polypeptides labeled with a fluorescent dye became noncovalently associated with cross-linked fibers, enabling visualization by fluorescence microscopy. Spectroscopy provided information on polymer chain conformation in solution and in fibers. Degradation of cross-linked fibers by different proteases has been demonstrated. Fibroblasts were cultured on cross-linked fiber mats to test basic cytocompatibility. Synthetic polypeptide fiber mats may be useful in applications in medicine, biotechnology, and other areas.

"In and out diffusion" hypothesis of exponential multilayer film buildup revisited.

A hypothesis concerning the exponential buildup of polyelectrolyte multilayer films prepared by layer-by-layer assembly has become widely accepted in the scientific community. This model was first introduced with experimental data in Langmuir. It was subsequently described in Proceedings of the National Academy of Sciences and extended and amended in papers in Langmuir and other journals. According to the "in and out diffusion" hypothesis, as it is called, or "common rule" of exponential multilayer film buildup, as it is widely regarded, "a diffusion-based buildup mechanism ... explains most of the exponential-like growth process of polyelectrolyte multilayers reported in the literature." The present work offers an alternative viewpoint to specific elements of the hypothesis and the model as a whole.

Insoluble synthetic polypeptide mats from aqueous solution by electrospinning.

Water-insoluble nanofiber mats of synthetic polypeptides of defined composition have been prepared by a process involving electrospinning from aqueous solution. L-ornithine is a physiological amino acid. Fibers of poly(L-ornithine) (PLO) were produced at feedstock concentrations above 20% w/v. Applied voltage and needle-to-collector distance were crucial for nanofiber formation. Attractive fibers were obtained at 35-40% w/v. Fiber diameter and mat morphology have been characterized by electron microscopy. Polymer cross-linking with glutaraldehyde (GTA) vapor rendered fiber mats water-insoluble. The study has yielded two advances on previous work in the area: avoidance of an animal source of peptides and avoidance of inorganic solvent.

Present and future prospects for polypeptide multilayer nanofilms in biotechnology and medicine.

Polypeptide multilayer nanofilms are a promising nanotechnology for commercial product development because the processes used to prepare them are simple, flexible, reliable, automatable, and scalable. Moreover, these materials can display a remarkable diversity of physical, chemical, and biological properties. Furthermore, the constituents of these nanofilms, in most cases the nanofilms themselves, and the fabrication process are environmentally benign. Nanofilm structure and function can be tailored to address two Grand Challenges of the US National Nanotechnology Initiative.

Reversibility of structural changes of polypeptides in multilayer nanofilms.

Structural properties of different polypeptide multilayer nanofilms fabricated at neutral pH have been analyzed by UV spectroscopy, circular dichroism spectroscopy (CD), and Fourier-transform infrared spectroscopy (FTIR). The various peptides studied exhibit a strong tendency to adopt a beta sheet conformation in the films. Changes in film structure on dehydration are completely reversed on rewetting. The time scale of reversibility is, however, substantially shorter for the polymer backbone than the side chains, as in protein folding.

From bench to bedside: successful translational nanomedicine: highlights of the Third Annual Meeting of the American Academy of Nanomedicine.

The Third Annual Meeting of the American Academy of Nanomedicine (AANM) was held at the University of California San Diego, in San Diego, California during September 7-8, 2007. The meeting was focused on successful translational nanomedicine: from bench to bedside. There were four keynote lectures and eight scientific symposiums in this meeting. The researchers and investigators reported the results and process of current nanomedicine research and approaches to clinical applications. The meeting provided exciting information for nanomedicine clinical-related researches and strategy for further development of nanomedicine research which will be benefits to clinical practice.

Controlled loading and release of a model drug from polypeptide multilayer nanofilms.

A major concern of medicine today is the sustained release of therapeutic compounds. Delivery vehicles for such compounds must be biocompatible. Ideally, loading a drug into the delivery vehicle will be a simple process, and vehicle properties will allow control over the drug release profile under desired conditions. Here, polypeptide multilayer nanofilms have been prepared by electrostatic layer-by-layer self-assembly to study the post-fabrication loading and release of a model therapeutic, methylene blue (MB). Drug loading and release have been characterized by optical spectroscopy for different peptide designs at different pH values, and film surface morphology has been characterized by atomic force microscopy (AFM). Differences in peptide structure have been found to influence MB loading and release under otherwise fixed conditions. Release is also influenced by pH, salt concentration, and number of "capping" layers. Although more research will be needed to exhaust the potential of polypeptide multilayer films, present results would suggest that the technology holds considerable promise for applications in medicine.

Stimulated release of small molecules from polyelectrolyte multilayer nanocoatings.

Free thiol-containing polyelectrolytes serve simultaneously as a material for self-assembly of a multilayer nanocoating and as a carrier of small molecules for release from the coating in response to an environmental cue.

Polypeptide multilayer nanofilm artificial red blood cells.

Reliable encapsulation of hemoglobin (Hb) within polypeptide multilayer nanofilms has been achieved by a template-based approach, and protein functionality has been demonstrated postencapsulation. The method is general in scope and could be useful for many other encapsulants. Met-Hb was adsorbed onto 5 microm-diameter CaCO3 microparticles, and the Hb-coated particles were encapsulated within a multilayer nanofilm of poly(L-glutamic acid) (PLGA) and poly(L-lysine) (PLL) by layer-by-layer assembly. The CaCO3 templates were then dissolved within the PLGA/PLL nanofilms by addition of ethylenediaminetetraacetic acid. Encapsulation of Hb was proved by fluorescence microscopy, the pH-dependence of retention of Hb was determined by visible wavelength absorbance, and conversion of the encapsulated met-Hb to deoxy-Hb and oxy-Hb was demonstrated by spectroscopic analysis of the Soret absorption peak under various conditions. It thus has been shown that control of Hb oxygenation within polypeptide multilayer nanofilm artificial cells is possible, and that Hb thus encapsulated can bind, release, and subsequently rebind molecular oxygen. This work therefore represents an advance in the development of polypeptide multilayer film artificial red blood cells.

Context dependence of the assembly, structure, and stability of polypeptide multilayer nanofilms.

Polyelectrolyte multilayer nanofilms and nanocomposites have shown considerable promise for the rational development of multifunctional materials with wide-ranging properties. Polypeptides are a distinctive and largely unexplored class of polyelectrolytes in this context. Methods now exist for the synthesis of peptides with control at the level of the amino acid sequence, and for the preparation of these polymers in massive quantities. Here, we analyze the roles of six designed 32mer peptides in the fabrication, structure, and stability of multilayer nanofilms prepared by layer-by-layer self-assembly. The data show that amino acid sequence and the specific combination of anionic and cationic peptides together have a marked impact on nanofilm growth behavior, secondary structure content, and density in experimental studies. The same factors determine physical properties of the corresponding interpolypeptide complexes in molecular dynamics simulations.