Alpha-synuclein (alphaS) is the primary component of Lewy bodies, the 
pathological hallmark of Parkinson's Disease. Aggregation of alphaS is thought 
to proceed from a primarily disordered state with nascent secondary structure 
through intermediate conformations to oligomeric forms and finally to mature 
amyloid fibrils. Low pH conditions lead to conformational changes associated 
with increased alphaS fibril formation. Here we characterize these structural 
and dynamic changes using solution state NMR measurements of secondary chemical 
shifts, relaxation parameters, residual dipolar couplings, and paramagnetic 
relaxation enhancement. We find that the neutralization of negatively charged 
side-chains eliminates electrostatic repulsion in the C-terminal tail of alphaS 
and leads to a collapse of this region at low pH. Hydrophobic contacts between 
the compact C-terminal tail and the NAC (non-amyloid-beta component) region are 
maintained and may lead to the formation of a globular domain. Transient 
long-range contacts between the C-terminus of the protein and regions N-terminal 
to the NAC region are also preserved. Thus, the release of long-range contacts 
does not play a role in the increased aggregation of alphaS at low pH, which we 
instead attribute to the increased hydrophobicity of the protein.