Nondestructive micro-patterning of proteinous occlusion bodies in water by femtosecond laser-induced mechanical force

Novel physical chemistry approaches in biophysical researches with advanced application of lasers: Detection and manipulation

Novel methodologies utilizing pulsed or intense CW irradiation obtained from lasers have a major impact on biological sciences. In this article, recent development in biophysical researches fully utilizing the laser irradiation is described for three topics, time-resolved fluorescence spectroscopy, time-resolved thermodynamics, and manipulation of the biological assemblies by intense laser irradiation. First, experimental techniques for time-resolved fluorescence spectroscopy are concisely explained in Section 2. As an example of the recent application of time-resolved fluorescence spectroscopy to biological systems, evaluation of the viscosity of lipid bilayer membranes is described. The results of the spectroscopic experiments strongly suggest the presence of heterogeneous membrane structure with two different viscosity values in liposomes formed by a single phospholipid. Section 3 covers the time-resolved thermodynamics. Thermodynamical properties are important to characterize biomolecules. However, measurement of these quantities for short-lived intermediate species has been impossible by traditional thermodynamical techniques. Recently, development of a spectroscopic method based on the transient grating method enables us to measure these quantities and also to elucidate reaction kinetics which cannot be detected by other spectroscopic methods. The principle of the measurements and applications to some protein reactions are reviewed. Manipulation and fabrication of supramolecues, amino acids, proteins, and living cells by intense laser irradiation are described in Section 4. Unconventional assembly, crystallization and growth, amyloid fibril formation, and living cell manipulation are achieved by CW laser trapping and femtosecond laser-induced cavitation bubbling. Their spatio-temporal controllability is opening a new avenue in the relevant molecular and bioscience research fields. This article is part of a Special Issue entitled "Biophysical Exploration of Dynamical Ordering of Biomolecular Systems" edited by Dr. Koichi Kato.

Time-Course Statistical Evaluation of Intercellular Adhesion Maturation by Femtosecond Laser Impulse

The maturation of intercellular adhesion is an essential process for establishing the signal transduction network in living cells. Although the maturation is naturally considered to enhance the signal transduction, the relationship between the signal transduction and the maturation process has not been revealed in detail using time-course data. Here, using a coculture of mast cells and neurites, differences in maturation between individual cells were estimated as a function of the adhesion strength by our original single-cell measurement method utilizing a laser-induced impulsive force. When an intense femtosecond laser is focused into a culture medium under a microscope, shock and stress waves are generated at the laser focal point that exert an impulsive force on individual cells. In our method, this impulse is used to break the adhesion between a mast cell and a neurite. The magnitude of the impulse is then quantified by a local force-measurement system utilizing an atomic force microscope, and the adhesion strength is estimated from the threshold of the impulse required to break the adhesion. The measurement is conducted within 1 min/cell, and thus, data on the individual differences of the adhesion strength can be obtained within only a few hours. Coculturing of neurites and mast cells for 4 h resulted in a specific adhesion that was stronger than the nonspecific adhesions between the substrate and mast cells. In the time-course investigation, we identified two distinct temporal patterns of adhesion: 1) the strength at 24 h was the same as the initial strength; and 2) the strength increased threefold from baseline and became saturated within 24 h. Based on these results, the distribution of CADM1 adhesion molecules in the neurites was suggested to be inhomogeneous, and the relationship between adhesion maturation and the signal-transduction process was considered.

In situ laser micropatterning of proteins for dynamically arranging living cells

This study shows the modification of the surface of polymer-layered glass substrates to form biofunctional micropatterns through femtosecond laser ablation in an aqueous solution. Domains of micrometer size on a substrate can be selectively converted from proteinphobic (resistant to protein adsorption) to proteinphilic, allowing patterning of protein features under physiological aqueous conditions. When femtosecond laser pulses (800 nm, 1 kHz, 200-500 nJ per pulse) were focused on and scanned on the substrate, which was glass covered with the proteinphobic polymer 2-methacryloyloxyethylphosphorylcholine (MPC), the surface became proteinphilic. Surface analysis by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) reveals that the laser ablates the MPC polymer. Extracellular matrix (ECM) proteins were bound to the laser-ablated surface by physisorption. Since femtosecond laser ablation is induced under physiological aqueous conditions, this approach can form micropatterns of functional ECM proteins with minimal damage. This method was applied to pattern collagen, laminin, and gelatin on the substrate. Removal of an ECM protein from the substrate followed by replacement with another ECM protein was achieved on demand at a specific location and time by the same laser ablation method. Living cells adhered to the fabricated domains where ECM proteins were arranged. The modification of patterning during cell culture was used to control cell migration and form arrays of different cells.

Immobilization of bioactive fibroblast growth factor-2 into cubic proteinous microcrystals (Bombyx mori cypovirus polyhedra) that are insoluble in a physiological cellular environment

The supramolecular architecture of the extracellular matrix and the disposition of its specific accessory molecules give rise to variable heterotopic signaling cues for single cells. Here we have described the successful occlusion of human fibroblast growth factor-2 (FGF-2) into the cubic inclusion bodies (FGF-2 polyhedra) of the Bombyx mori cytoplasmic polyhedrosis virus (BmCPV). The polyhedra are proteinous cubic crystals of several microns in size that are insoluble in the extracellular milieu. Purified FGF-2 polyhedra were found to stimulate proliferation and phosphorylation of p44/p42 mitogen-activated protein kinase in cultured fibroblasts. Moreover, cellular responses were blocked by a synthetic inhibitor of the FGF signaling pathway, SU5402, suggesting that FGF-2 polyhedra indeed act through FGF receptors. Furthermore, FGF-2 polyhedra retained potent growth stimulatory properties even after desiccation. We have demonstrated that BmCPV polyhedra microcrystals that occlude extracellular signaling proteins are a novel and versatile tool that can be employed to analyze cellular behavior at the single cell level.