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Published on: May 25, 2018
The substrate range of tripeptidyl-peptidase I
1Department of Histopathology, St George's Hospital Medical School, Cranmer Terrace, London SW17 0RE, UK.
Insights
Tripeptidyl-peptidase I (TPP-I) degrades small peptides but not proteins, with a size cut-off generally between 4.5 and 6 kDa. This enzyme
Area of Science:
- Biochemistry
- Enzymology
- Molecular Biology
Background:
- Tripeptidyl-peptidase I (TPP-I) is an exopeptidase involved in peptide degradation.
- Mutations in TPP-I cause late infantile neuronal ceroid lipofuscinosis (CLN2), a neurodegenerative disorder.
- The precise physiological substrates and specificity of TPP-I remain incompletely understood.
Purpose of the Study:
- To investigate the substrate size range and specificity of Tripeptidyl-peptidase I (TPP-I).
- To elucidate the factors determining TPP-I's selectivity for peptide degradation.
- To explore potential mechanisms for TPP-I's size selectivity based on peptidase structures.
Main Methods:
- Enzymatic digestion assays using a range of peptides with varying sizes and structures.
- Analysis of peptide degradation products to determine TPP-I activity.
- Comparative analysis with known peptidase structures to infer mechanisms of selectivity.
Main Results:
- TPP-I effectively degrades small peptides, particularly those with extended N-terminal domains.
- A general size cut-off for TPP-I activity was observed between peptide masses of 4.5 kDa and 6 kDa.
- Structured peptides and larger molecules were resistant to TPP-I digestion, indicating substrate specificity.
Conclusions:
- TPP-I exhibits size-dependent substrate specificity, primarily degrading smaller peptides.
- The findings provide insights into the physiological role of TPP-I and its substrate preferences.
- Understanding TPP-I's selectivity may aid in understanding CLN2 pathogenesis and developing therapeutic strategies.
Abstract:
Tripeptidyl-peptidase I (TPP-I) is an exopeptidase which removes tripeptides from the N-terminus of peptides. Mutations in TPP-I are responsible for late infantile neuronal ceroid lipofuscinosis (CLN2). The nature of the physiological substrates and the range and specificity of the enzyme are unclear. Previous experiments suggest that the enzyme can degrade small peptides but not proteins. Digestion of a range of peptides of different size by TTP-I suggests that the enzyme will degrade small peptides with an extended N-terminal domain but not structured peptides. In general, this cut-off occurs between masses of 4.5 kDa and 6 kDa. Reference to the structures of other peptidases suggests a mechanism for this size selectivity.
