Event In Biological Processes Research Articles

Biorecognition in Organic Field Effect Transistors Biosensors: The Role of the Density of States of the Organic Semiconductor.

Biorecognition is a central event in biological processes in the living systems that is also widely exploited in technological and health applications. We demonstrate that the Electrolyte Gated Organic Field Effect Transistor (EGOFET) is an ultrasensitive and specific device that allows us to quantitatively assess the thermodynamics of biomolecular recognition between a human antibody and its antigen, namely, the inflammatory cytokine TNFα at the solid/liquid interface. The EGOFET biosensor exhibits a superexponential response at TNFα concentration below 1 nM with a minimum detection level of 100 pM. The sensitivity of the device depends on the analyte concentration, reaching a maximum in the range of clinically relevant TNFα concentrations when the EGOFET is operated in the subthreshold regime. At concentrations greater than 1 nM the response scales linearly with the concentration. The sensitivity and the dynamic range are both modulated by the gate voltage. These results are explained by establishing the correlation between the sensitivity and the density of states (DOS) of the organic semiconductor. Then, the superexponential response arises from the energy-dependence of the tail of the DOS of the HOMO level. From the gate voltage-dependent response, we extract the binding constant, as well as the changes of the surface charge and the effective capacitance accompanying biorecognition at the electrode surface. Finally, we demonstrate the detection of TNFα in human-plasma derived samples as an example for point-of-care application.

Fine-Tuning of the Actin Cytoskeleton and Cell Adhesion During Drosophila Development by the Unconventional Guanine Nucleotide Exchange Factors Myoblast City and Sponge.

The evolutionarily conserved Dock proteins function as unconventional guanine nucleotide exchange factors (GEFs). Upon binding to engulfment and cell motility (ELMO) proteins, Dock-ELMO complexes activate the Rho family of small GTPases to mediate a diverse array of biological processes, including cell motility, apoptotic cell clearance, and axon guidance. Overlapping expression patterns and functional redundancy among the 11 vertebrate Dock family members, which are subdivided into four families (Dock A, B, C, and D), complicate genetic analysis. In both vertebrate and invertebrate systems, the actin dynamics regulator, Rac, is the target GTPase of the Dock-A subfamily. However, it remains unclear whether Rac or Rap1 are the in vivo downstream GTPases of the Dock-B subfamily. Drosophila melanogaster is an excellent genetic model organism for understanding Dock protein function as its genome encodes one ortholog per subfamily: Myoblast city (Mbc; Dock A) and Sponge (Spg; Dock B). Here we show that the roles of Spg and Mbc are not redundant in the Drosophila somatic muscle or the dorsal vessel. Moreover, we confirm the in vivo role of Mbc upstream of Rac and provide evidence that Spg functions in concert with Rap1, possibly to regulate aspects of cell adhesion. Together these data show that Mbc and Spg can have different downstream GTPase targets. Our findings predict that the ability to regulate downstream GTPases is dependent on cellular context and allows for the fine-tuning of actin cytoskeletal or cell adhesion events in biological processes that undergo cell morphogenesis.

Biological applications of picosecond spectroscopy.

Technological advances in picosecond spectroscopy have permitted the mechanisms of various chemical, physical and biological processes to be elucidated and understood to a greater degree than ever before. By means of picosecond emission, absorption and Raman spectroscopy, one can probe and measure directly the transient intermediates and kinetics of primary events in complex biological processes. A description of two current types of laser systems--solid-state and synchronously pumped dye lasers--and their application to determining the primary events in the biological processes of dissociation of oxy- and carboxymyoglobin, excited-state relaxation of porphyrins and visual transduction, illustrate the power of picosecond spectroscopy.

Does Ca2+ cause fusion or lysis of unilamellar lipid vesicles?

MEMBRANE fusion is the central event in biological processes as diverse as secretion, fertilisation, endocytosis and pathological cell fusion, but as yet its mechanism is poorly understood1. To elucidate this mechanism, bilayer phospholipid vesicles have been used extensively as models for interacting biomem-branes2–5. As a result of studies involving differential scanning calorimetry and freeze-fracture electron microscopy, it has been suggested that vesicles made from acidic phospholipids can fuse when exposed to divalent cations3–6. For phosphatidylserine vesicles, the ‘critical’ Ca2+ concentration for membrane fusion seems to be ∼ 1 mM, at which concentration a drastic increase in the permeability of the vesicle membranes has also been reported3. The techniques used to demonstrate ‘fusion’ in this system do not exclude molecular mixing of interacting membranes by mechanisms other than genuine fusion. In the latter case, the membrane-bounded internal compartments of two separate vesicles must become confluent in a process which transfers the contents of the initial vesicles to the resulting vesicle. It is possible, however, that Ca2+ may cause rupture of the lipid vesicles, with subsequent reassembly of the membrane fragments to form larger non-vesicular structures. If this is occurring, bilayer vesicles are poor paradigms for biological membrane fusion. One may predict the likelihood of vesicle fusion by calculating their energy of interaction due to electrostatic repulsion and electrodynamic attraction7. This approach shows that the addition of 1 mM Ca2+ to a suspension of phosphatidylserine vesicles is unlikely to reduce electrostatic repulsion between liposomes sufficiently for any but a fraction of the smallest ones to approach to 0.8 nm separation. This finding suggests that vesicles cannot approach closely enough to fuse and supports the notion that Ca2+ may initiate vesicle lysis and reassembly. We report here experimental support for vesicle lysis, based on the redistribution of a marker for the aqueous phase between vesicles and the external compartment on exposure to divalent cations.