title: The specificity of lysosomal tripeptidyl peptidase-I determined by its action on angiotensin-II analogues.
abstract: Tripeptidyl peptidase-I (TPP-I) is a lysosomal peptidase which cleaves tripeptides from the N-terminus of peptides. The function of the enzyme is unclear but its importance is demonstrated by the fact that mutations in TPP-I are responsible for late infantile neuronal ceroid lipofuscinosis, a lethal lysosomal storage disease. As a step towards identifying its natural substrates, we have used a series of synthetic peptides, based on angiotensin-II, to explore the effects of peptide chain length and the effects of amino acid substitutions at the P1 and P1' positions on the rate of catalysis. With the exception of angiotensin-(1-8) (angiotensin-II), which is a relatively poor substrate for TPP-I, the rate of catalysis increases with increasing chain length. K(cat)/K(m) values increase 50-fold between angiotensin-(1-5) and angiotensin-(1-14). TPP-I shows little specificity for the nature of the amino acids in the P1 and P1' positions, K(cat)/K(m) values varying only 5-fold for a range of substitutions. However, Pro or Lys in the P1 position and Pro in the P1' positions are incompatible with TPP-I activity. These observations suggest that TPP-I is a non-specific, but essential, peptidase involved in the latter stages of lysosomal protein degradation.
authors.affiliation: Department of Cellular Pathology, St George's Hospital Medical School, Cranmer Terrace, SW17 0RE, London, UK. mwarburt@sghms.ac.uk
authors.forename: M J
authors.initials: MJ
authors.lastname: Warburton
authors.forename: F
authors.initials: F
authors.lastname: Bernardini
mesh_terms: D019943:Amino Acid Substitution; D000626:Aminopeptidases; D000804:Angiotensin II / Q000031:analogs & derivatives / Q000737:chemistry* / Q000187:drug effects; D000818:Animals; D002384:Catalysis; D002851:Chromatography, High Pressure Liquid; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; D010450:Endopeptidases / Q000737:chemistry* / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008247:Lysosomes / Q000201:enzymology*; D009472:Neuronal Ceroid-Lipofuscinoses / Q000201:enzymology; D010455:Peptides / Q000737:chemistry / Q000187:drug effects; D057057:Serine Proteases; D013329:Structure-Activity Relationship; D013379:Substrate Specificity / Q000502:physiology; D013552:Swine; D000091346:Tripeptidyl-Peptidase 1
chemical_list: D010455:Peptides; D000091346:Tripeptidyl-Peptidase 1; D000804:Angiotensin II; D010450:Endopeptidases; D057057:Serine Proteases; D000626:Aminopeptidases; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases