alpha-synuclein and 1-anilino-8-naphthalenesulfonate

The effect of macromolecular crowding on protein structure and dynamics has mostly been explained on the basis of the excluded volume effect, its origin being entropic. In recent times a progressive shift in this view has been taking place with increasing emphasis on soft interactions that are enthalpic by nature. Using very low concentrations (1-10 g/L) of both synthetic (dextran- and poly(ethylene glycol) (PEG)-based) and protein (α-synuclein and myoglobin)-based crowders, we have shown that the solvation of probe molecule ANS (1-anilinonapthalene-8-sulfonate) bound to serum proteins bovine serum albumin (BSA) and human serum albumin (HSA) is significantly modulated in both a protein- and crowder-dependent fashion. Since under such conditions the effect of excluded volume is appreciably low, we propose that our observations are direct evidence of soft interactions between the macromolecular crowding agents used and the serum proteins. Moreover, our data reveal, that since at these low crowder concentrations major perturbations to the protein structure are unlikely to take place while minor perturbations might not be readily visible, protein solvation provides a unique spectral signature for capturing such local dynamics, thereby allowing one to decouple hard-sphere interactions from soft sphere ones. Furthermore, since fast fluctuations are known to play a major role in determining the functional characteristics of proteins and enzymes, our results suggest that such motions are prone to be modulated even when the cellular crowding conditions are quite relaxed. In other words, by the time the excluded volume effects come into the picture in the physiological milieu, modulations of functionally important protein motions that need a relatively lower activation energy have already taken place as a result of the aforementioned enthalpic (soft) interactions.

Topics: alpha-Synuclein; Anilino Naphthalenesulfonates; Animals; Cattle; Dextrans; Humans; Models, Molecular; Molecular Structure; Myoglobin; Polyethylene Glycols; Serum Albumin; Solubility

Alpha-synuclein aggregation is a hallmark pathological feature in Parkinson's disease (PD). The conversion of alpha-synuclein from a soluble monomer to an insoluble fibril may underlie the neurodegeneration associated with PD. Redox-active metal ions such as iron (Fe) and copper (Cu) are known to enhance alpha-synuclein fibrillogenesis. In the present investigation, we analyzed the binding efficiency of Cu and Fe to alpha-synuclein by fluorescence studies. It is interesting to note that Cu and Fe showed differential binding pattern toward alpha-synuclein (wild type and A30P, A53T, and E46K mutant forms) as revealed by intrinsic tyrosine fluorescence, thioflavin-T fluorescence, 1-anilino-8-naphthalenesulfonate-binding studies, and scatchard plot analysis. The experimental data might prove useful in understanding the hierarchy of metals binding to alpha-synuclein and its role in neurodegeneration.

Topics: alpha-Synuclein; Anilino Naphthalenesulfonates; Benzothiazoles; Binding Sites; Copper; Fluorescence; Fluorescent Dyes; Humans; Iron; Protein Binding; Thiazoles; Tyrosine

The aggregation of alpha-synuclein is believed to be a critical step in the etiology of Parkinson's disease. A variety of biophysical techniques were used to investigate the aggregation and fibrillation of alpha-synuclein in which one of the four intrinsic Tyr residues was replaced by Trp, and two others by Phe, in order to permit fluorescence resonance energy transfer (FRET) between residues 39 (Tyr) and 125 (Trp). The mutant Y125W/Y133F/Y136F alpha-synuclein (one Tyr, one Trp) showed fibrillation kinetics similar to that of the wild-type, as did the Y125F/Y133F/Y136F (one Tyr, no Trp) and Y39F/Y125W/Y133F/Y136F (no Tyr, one Trp) mutants. Time-dependent changes in FRET, Fourier transform infrared, Trp fluorescence, dynamic light-scattering and other probes, indicate the existence of a transient oligomer, whose population reaches a maximum at the end of the lag time. This oligomer, in which the alpha-synuclein is in a partially folded conformation, is subsequently converted into fibrils, and has physical properties that are distinct from those of the monomer and fibrils. In addition, another population of soluble oligomers was observed to coexist with fibrils at completion of the reaction. The average distance between Tyr39 and Trp125 decreases from 24.9A in the monomer to 21.9A in the early oligomer and 18.8A in the late oligomer. Trp125 remains solvent-exposed in both the oligomers and fibrils, indicating that the C-terminal domain is not part of the fibril core. No FRET was observed in the fibrils, due to quenching of Tyr39 fluorescence in the fibril core. Thus, aggregation of alpha-synuclein involves multiple oligomeric intermediates and competing pathways.

Topics: alpha-Synuclein; Anilino Naphthalenesulfonates; Benzothiazoles; Fluorescence Resonance Energy Transfer; Fluorescent Dyes; Humans; Mutagenesis, Site-Directed; Nerve Tissue Proteins; Parkinson Disease; Protein Structure, Secondary; Spectroscopy, Fourier Transform Infrared; Synucleins; Thiazoles; Tryptophan; Tyrosine