Biophysical view of the role of interfaces in biomolecular recognition

An anti-fouling aptasensor for detection of thrombin by dual polarization interferometry

An anti-fouling surface was designed to effectively resist nonspecific protein adsorption using dual polarization interferometry, based on which the aptasensor for detection of thrombin was fabricated according to the specific interaction between thrombin and its 15-mer aptamer.

The structure of VgrG1 fromPseudomonas aeruginosa, the needle tip of the bacterial type VI secretion system

The type VI secretion system (T6SS) is a mechanism that is commonly used by pathogenic bacteria to infect host cells and for survival in competitive environments. This system assembles on a core baseplate and elongates like a phage puncturing device; it is thought to penetrate the target membrane and deliver effectors into the host or competing bacteria. Valine–glycine repeat protein G1 (VgrG1) forms the spike at the tip of the elongating tube formed by haemolysin co-regulated protein 1 (Hcp1); it is structurally similar to the T4 phage (gp27)3–(gp5)3puncturing complex. Here, the crystal structure of full-length VgrG1 fromPseudomonas aeruginosais reported at a resolution of 2.0 Å, which through a trimeric arrangement generates a needle-like shape composed of two main parts, the head and the spike, connectedviaa small neck region. The structure reveals several remarkable structural features pointing to the possible roles of the two main segments of VgrG1: the head as a scaffold cargo domain and the β-roll spike with implications in the cell-membrane puncturing process and as a carrier of cognate toxins.

In vitro phototoxicity of ultradeformable liposomes containing chloroaluminum phthalocyanine against New World Leishmania species

The use of photodynamic therapy (PDT) against cutaneous leishmaniasis (CL) based on chloroaluminum phthalocyanine (ClAlPc) is a promissory alternative therapy. The main purpose of this article was to assess the internalization and in vitro phototoxic activities of ClAlPc encapsulated in ultradeformable liposomes (UDL-ClAlPc) in Leishmania parasites and mammalian cells. Cell internalization was determined by fluorescence microscopy, cell and parasite damage by standard MTT or direct microscopic analysis and a phototoxic index (PI) was calculated as the compound activity (IC(50)) at 0 J/cm(2)/IC(50) at 17 J/cm(2). Liposomal and free ClAlPc were internalized by infected and non-infected THP-1 cells and co-localized in the mitochondria. Treatment of UDL-ClAlPc was almost 10 times more photoactive than free ClAlPc on THP-1 cells and promastigotes and intracellular amastigotes of Leishmania chagasi and Leishmania panamensis. Liposomal compounds were active on non-irradiated and irradiated cells however PI higher than 50 were calculated. PI for amphotericin B referential drug were lower than 1.2. Empty liposomes tested at the same lipid concentration of active ClPcAl-liposomes were non-toxic. Upon photodynamic treatment a nonselective-parasite activity against intracellular amastigotes were observed and loss of membrane integrity resulting in a release of parasites was detected. Further studies oriented to evaluate both the state of infection after PDT and the effectiveness of UDL as delivery vehicles of ClAlPc in CL experimental models are required.

Development of a constant surface pressure penetration langmuir balance based on axisymmetric drop shape analysis

A new constant pressure pendant-drop penetration surface balance has been developed combining a pendant-drop surface balance, a rapid-subphase-exchange technique, and a fuzzy logic control algorithm. Beside the determination of insoluble monolayer compression-expansion isotherms, it allows performance of noninvasive kinetic studies of the adsorption of surfactants added to the new subphase onto the free surface and of the adsorption/penetration/reaction of the former onto/into/with surface layers, respectively. The interfacial pressure pi is a fundamental parameter in these studies: by working at constant pi one controls the height of the energy barrier to adsorption/penetration and can select different regimes and steps of the adsorption/penetration process. In our device a solution drop is formed at the tip of a coaxial double capillary, connected to a double microinjector. Drop profiles are extracted from digital drop micrographs and fitted to the equation of capillarity, yielding pi, the drop volume V, and the interfacial area A. pi is varied changing V (and hence A) with the microinjector. Control is based on a case-adaptable modulated fuzzy-logic PID algorithm able to maintain constant pi (or A) under a wide range of experimental conditions. The drop subphase liquid can be exchanged quantitatively by the coaxial capillaries. The adsorption/penetration/reaction kinetics at constant pi are then studied monitoring A(t), i.e., determining the relative area change necessary at each instant to compensate the pressure variation due to the interaction of the surfactant in the subsurface with the surface layer. A fully Windows-integrated program manages the whole setup. Examples of experimental protein adsorption and monolayer penetration kinetics are presented.

Crystal attachment to injured renal collecting duct cells: influence of urine proteins and pH

BACKGROUND

The attachment of crystals to injured kidney epithelium is thought to be a necessary event in the development of urolithiasis. In vivo, the crystals are coated with urinary macromolecules that define the surface properties of the crystals. The present study examines the influence of coating of calcium oxalate crystals with urinary macromolecules on their attachment to both healthy (polarized) and injured (nonpolarized) primary inner medullary collecting duct (IMCD) cells.

METHODS

Calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD) crystals were coated with urine macromolecules by incubating the crystals in urine from normal healthy volunteers at pH 5, 6, and 7. The level of attachment of the coated crystals to IMCD cells was also determined at pH 5, 6, and 7. The adsorbed proteins were extracted from the crystal surfaces and separated by gel electrophoresis.

RESULTS

The coating of calcium oxalate crystals with urine proteins greatly reduced the attachment of crystals to both control and injured IMCD cells. At pH levels below 6, the crystals readily attached to injured cells. Extraction and separation of the adsorbed proteins showed that both COM and COD crystals adsorbed a similar array of proteins. At pH 5 and 6, several trace proteins were adsorbed to the crystals and were not apparent at pH 7.

CONCLUSION

The coating of crystals with urine macromolecules greatly reduces the attachment of the crystals to normal healthy epithelia. The coating and attachment of the crystals below pH 6 enhances the attachment to injured cells. The enhanced crystal attachment could possibly be associated with one or more proteins adsorbed to the crystal surface that are not adsorbed to the crystals at higher pH.

Hydration-driven transport of deformable lipid vesicles through fine pores and the skin barrier

We studied aggregate transport through semipermeable, nano-porous barriers experimentally and theoretically. By measuring and modeling the effect of hydration gradient across such barriers, spontaneous transbarrier transport of suitable lipid aggregates in vesicular form was proven to be driven by partial aggregate dehydration at the application site. By generalizing the Onsager transport model we derived a set of equations that rationalize all pertinent observations. Dehydration-induced vesicle motion starts with a lag time. This corresponds to the time needed to reach the limiting vesicle hydration; both are proportional to the starting excess water volume and decrease with increasing relative humidity at application site. The rate of transbarrier transport is insensitive to these parameters but increases with vesicle deformability and volume exchange capability. Both these properties depend on membrane composition. Reversible demixing of bilayer components is the cause of nonlinear bilayer characteristics and also potentially affects the effective membrane hydrophilicity. High hydrophilicity of vesicle surface and extreme aggregate shape adaptability together are necessary for successful material transport across the skin. This demonstrates the significance of basic biophysical investigations for better understanding of biological systems and for the practical use of artificial, nature-inspired carriers in drug delivery.

Study of the behavior of biological molecules in a thin gap by refractive index and force measurements with an automatic surface force apparatus

The automation of the mica surface displacement of a surface force apparatus (SFA) increases the accuracy of the intermolecular force measurements that is obtained without the presence of the experimenter. The automatic device cancels any thermal drift and the stability of the mica surfaces is optimum. The distance between the mica surfaces is measured by Tolansky multiple-beam interferometry (FECO method) which offers a sensitivity of 0.1 nm in the direction perpendicular to the plane of contact area. The mean refractive index of the medium between the mica plates is computed from simultaneous measurements of the wavelengths of two successive fringes of equal chromatic order (FECO). A conversion of an isotropic molecule to another anisotropic molecule can be identified from the variations of the refractive index. In good conditions, we can compute the local concentration of the molecules in the gap of the device, and estimate the Young's modulus of a protein.