Lewy bodies, neuropathological hallmarks of Parkinson's disease and dementia 
with Lewy bodies, comprise alpha-synuclein filaments and other less defined 
proteins. Characterization of Lewy body proteins that interact with 
alpha-synuclein may provide insight into the mechanism of Lewy body formation. 
Double immunofluorescence labeling and confocal microscopy revealed 
approximately 80% of cortical Lewy bodies contained microtubule-associated 
protein 1B (MAP-1B) that overlapped with alpha-synuclein. Lewy bodies were 
isolated using an immunomagnetic technique from brain tissue of patients dying 
with dementia with Lewy bodies. Lewy body proteins were resolved by 
polyacrylamide gel electrophoresis. Immunoblotting confirmed the presence of 
MAP-1B and alpha-synuclein in purified Lewy bodies. Direct binding studies 
revealed a high affinity interaction (IC(50) approximately 20 nm) between MAP-1B 
and alpha-synuclein. The MAP-1B-binding sites were mapped to the last 45 amino 
acids of the alpha-synuclein C terminus. MAP-1B also bound in vitro assembled 
alpha-synuclein fibrils. Thus, MAP-1B may be involved in the pathogenesis of 
Lewy bodies via its interaction with monomeric and fibrillar alpha-synuclein.