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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 27, Number 7
BKCSDE 27(7)
July 20, 2006 

Regulation of m-Calpain Activity by α-Synuclein and Its C-terminal Fragment (α-syn61-140)
In-Hwan Lee, Hyun Jin Kim, Choong-Hwan Lee, Seung R. Paik*
α-Synuclein, Calpain, Proteolysis, Calpain regulator, Parkinson’s disease
The m-calpain activity hydrolyzing a fluorogenic substrate of N-Succinyl-Leu-Leu-Val-Tyr-7-amino-4-methylcourmarin (LLVY-AMC) was significantly stimulated by more than two-fold in the presence of 5 μM α-synuclein at 15 ºC. The stimulation was also confirmed with azocasein. The stimulation of the peptide hydrolyzing activity required structural intactness of α-synuclein since the C-terminally or N-terminally modified proteins such as β-synuclein, α-syn1-97, and α-syn61-140 did not increase the proteolytic activity. Instead, however, the N-terminally truncated α-syn61-140 was shown to drastically suppress the calpain activity. Since the N-terminal truncation was known to be the primary cleaving event of calpain-mediated proteolysis of α-synuclein and the α-syn61-140 has been demonstrated to be resistant against the calpain digestion, it has been proposed that the intracellular calpain activity could be regulated in a reciprocal manner by α-synuclein and its proteolyzed C-terminal fragment. Based on the results, a possible physiological function of α-synuclein has been suggested as a calpain regulator which contains both stimulatory and inhibitory activities.
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