Conformational dynamics of alpha-synuclein:insights from mass spectrometry

The aggregation and deposition of alpha-synuclein in Lewy bodies is associated with the progression of Parkinson's disease. Here, Mass Spectrometry (MS) is used in combination with Ion Mobility (IM), chemical crosslinking and Electron Capture Dissociation (ECD) to probe transient structural elements of alpha-synuclein and its oligomers. Each of these reveals different aspects of the conformational heterogeneity of this 14 kDa protein. IM-MS analysis indicates that this protein is highly disordered, presenting in positive ionisation mode with a charge state range of 5 <= z <= 21 for the monomer, along with a collision cross section range of similar to 1600 angstrom(2)). Chemical crosslinking applied in conjunction with IM-MS captures solution phase conformational families enabling comparison with those exhibited in the gas phase. Crosslinking IM-MS identifies 3 distinct conformational families, Compact (similar to 1200 angstrom(2)), Extended (similar to 1500 angstrom(2)) and Unfolded (similar to 2350 angstrom(2)) which correlate with those observed in solution. ECD-Fourier Transform-Ion Cyclotron Resonance Mass Spectrometry (ECD-FT-ICR MS) highlights the effect of pH on alpha-synuclein structure, identifying the conformational flexibility of the N and C termini as well as providing evidence for structure in the core and at times the C terminus. A hypothesis is proposed for the variability displayed in the structural rearrangement of alpha-synuclein following changes in solution pH. Following a 120 h aggregation time course, we observe an increase in the ratio of dimer to monomer, but no gross conformational changes in either, beyond the significant variations that are observed day-to-day from this conformationally dynamic protein

Photophysics of Supercomplexes. A Laser-Induced Optoacoustic Study of the Adducts formed between Ru(bpy)(CN)42- and Polyaza Macrocycles

In aqueous solution, the energy content of the triplet metal-to-ligand charge transfer _3MLCT. state, as deter- mined by laser-induced optoacoustic spectroscopy, for both 1:1 supercomplexes _wRu_bpy._CN.4 xPw24xane-wN6H6 x44q and wRu_bpy._CN.4xPw32xane-wN8H8x46q are similar to that for free Ru_bpy._CN.42y _223"8 kJrmol.. The reduction of the structural volume change upon formation of the 3MLCT state in the order Ru_bpy._CN.2y _14.9 mlrmol., _wRu_bpy._CN. x 4 4 Pw32xane-wN8H8x46q _5.2 mlrmol. and _wRu_bpy._CN.4 xPw24xane-wN6H6 x44q _2.5 mlrmol. is attributed to the rigidity of the macrocycle cavity. The 3MLCT state lifetime increase from 104 ns for Ru_bpy._CN.2y to 150 ns for _wRu_bpy._CN. xP 4 4 w24xane-wN6H6x44q and 182 ns for _wRu_bpy._CN.4 xPw32xane-wN8H8x46q is due to the decrease in the number of CN groups free to form hydrogen bonds with water: four, one, and none, respectively

Photophysical, photochemical and antibacterial photosensitizing properties of a novel octacationic Zn(II)-phthalocyanine

A novel Zn(II)-phthalocyanine (1). peripherally substituted with four bis(N,N,N-trimethyl)amino-2-propyloxy groups prepared by chemical synthesis is shown to be an efficient photodynamic sensitizer with a quantum yield of 0.6 for singlet oxygen generation in neat water, which is reduced to about 0.3 in phosphate-buffered saline. The physicochemical properties of 1 in both the ground and the electronically excited states strongly depend on the nature of the medium; in particular, aggregation of 1 was favoured by polar media of high ionic strength. Compound 1 exhibited an appreciable affinity for a typical Gram-positive bacterium (Staphylococcus aureus) and a typical Gram-negative bacterium (Escherichia coli). Both bacterial strains were extensively inactivated upon 5 min-irradiation with 675 nm light in the presence of 1 microM photosensitizer, even though the binding of 1 to the two bacterial cells appears to occur according to different pathways. In particular, E. coli cells underwent initial photodamage at the level of specific proteins in the outer wall, thus promoting the penetration of the photosensitizer to the cytoplasmic membrane where some enzymes critical for cell survival were inactivated

Gum arabic microcapsules as protectors of the photoinduced degradation of riboflavin in whole milk

Microcapsules (MC) made with Gum Arabic (GA) as shell material without and with beta-carotene (bc) as core material were prepared by the spray-dried technique. The effect of these MC on the photodegradation of Riboflavin (Rf) in whole milk by fluorescent daylight lamp irradiation was evaluated at storage temperature of 4 \ub0C. The additions of 1.37 mg/mL of MC without bc (MC-GA) and with containing 0.54 microg/mL of bc (MC-bc-GA) decreased the apparent first order rate constant of Rf photodegradation by approximately 26 and 30%, respectively. A systematic kinetic and mechanistic analysis of the results indicates that the global protective effect of the MC is mainly due to thecombination of quenching of electronically excited triplet state of Rf and scavenging of the photogenerated reactive oxygen species (ROS), such as singlet molecular oxygen, superoxide radical anion and hydroxyl radical. A minor contribution to the photoprotective effect can be also associated with inner-filter effect exerted by the MC that blocks partially the direct excitation of Rf. These results allow concluding that photodegradation of Rf in milk can be considerably reduced by the addition of small amounts of MC, avoiding large losses in the nutritional value of milk