Title : Common G102S polymorphism in
chitotriosidase differentially affects activity towards 4-methylumbelliferyl substrates
Abstract :
- Chitotriosidase (CHIT1 ) is a chitinase that is secreted by activated macrophages
- Plasma chitotriosidase activity reflects the presence of lipid-laden macrophages in patients with Gaucher disease
- CHIT1 activity can be conveniently measured using fluorogenic 4-methylumbelliferyl (4MU)-chitotrioside or 4MU-chitobioside as the substrate, however, nonsaturating concentrations have to be used because of apparent substrate inhibition
- Saturating substrate concentrations can, however, be used with the newly designed substrate 4MU-deoxychitobioside
- We studied the impact of a known polymorphism, G102S, on the catalytic properties of CHIT1
- The G102S allele was found to be common in type I Gaucher disease patients in the Netherlands ( approximately 24% of alleles)
- The catalytic efficiency of recombinant Ser102 CHIT1 was approximately 70% that of wild-type Gly102 CHIT1 when measured with 4MU-chitotrioside at a nonsaturating concentration
- However, the activity was normal with 4MU-deoxychitobioside as the substrate at saturating concentrations, consistent with predictions from molecular dynamics simulations
- In conclusion, interpretation of CHIT1 activity measurements with 4MU-chitotrioside with respect to CHIT1 protein concentrations depends on the presence of Ser102 CHIT1 in an individual, complicating estimation of the body burden of storage macrophages
- Use of the superior 4MU-deoxychitobioside substrate avoids such complications because activity towards this substrate under saturating conditions is not affected by the G102S substitution