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Published on: September 17, 2008
Specific substrate for CLN2 protease/tripeptidyl-peptidase I assay
M A Junaid1, S S Brooks, R K Pullarkat
1Department of Developmental Biochemistry, New York State Institute for Basic Research in Developmental Disabilities, 1050 Forest Hill Road, Staten Island, NY 10314, USA. majunaid@aol.com
Summary
A new assay using G-F-F-L-AFC substrate accurately detects late infantile neuronal ceroid lipofuscinosis (LINCL) and identifies carriers. This method offers high specificity for CLN2 protease (CLN2p) activity, crucial for diagnosing this neurodegenerative disorder.
Area of Science:
- Biochemistry
- Genetics
- Neuroscience
Background:
- Late Infantile Neuronal Ceroid Lipofuscinosis (LINCL, CLN2) is a fatal neurodegenerative disease caused by mutations in the CLN2 gene, affecting CLN2 protease (CLN2p) or tripeptidyl peptidase I (TPP-I) function.
- Previous assays using various substrates showed limited accuracy in identifying carriers and quantifying residual CLN2p/TPP-I activity in LINCL patients.
Purpose of the Study:
- To develop and validate a highly specific assay for CLN2p/TPP-I activity using the G-F-F-L-AFC substrate.
- To apply this assay for the prenatal and postnatal diagnosis of LINCL and the identification of heterozygote carriers.
Main Methods:
- Utilized the G-F-F-L-AFC substrate to measure CLN2p/TPP-I enzymatic activity in leukocytes.
- Compared enzyme activities in healthy controls, heterozygote carriers, and LINCL patients.
Main Results:
- The G-F-F-L-AFC assay demonstrated high specificity for CLN2p/TPP-I.
- Leukocyte CLN2p/TPP-I activities were significantly lower in heterozygote carriers (918 +/- 253 nmol/h/mg protein) compared to controls (1995 +/- 154 nmol/h/mg protein).
- Most LINCL patients showed undetectable CLN2p/TPP-I activity, with two exhibiting less than 2% residual activity and delayed symptoms.
Conclusions:
- The G-F-F-L-AFC substrate provides a highly specific and reliable method for CLN2p/TPP-I assay.
- This assay is effective for diagnosing LINCL and identifying carriers, aiding in prenatal and postnatal genetic counseling.
