Biosynthesis, Glycosylation, and Enzymatic Processingin Vivo of Human Tripeptidyl-peptidase I

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Tripeptidyl peptidase I (TPP I) is the first mammalian representative of a family of pepstatin-insensitive serine-carboxyl proteases, or sedolisins. The enzyme acts in lysosomes, where it sequentially removes tripeptides from the unmodified N terminus of small, unstructured polypeptides. Naturally occurring mutations in TPP I underlie a neurodegenerative disorder of childhood, classic late infantile neuronal ceroid lipofuscinosis (CLN2). Generation of mature TPP I is associated with removal of a long prosegment of 176 amino acid residues from the zymogen. Here we investigated the inhibitory properties of TPP I prosegment expressed and isolated from Escherichia coli toward its cognate protease. We show that the TPP I prosegment is a potent, slow-binding inhibitor of its parent enzyme, with an overall inhibition constant in the low nanomolar range. We also demonstrate the protective effect of the prosegment on alkaline pH-induced inactivation of the enzyme. Interestingly, the inhibitory properties of TPP I prosegment with the introduced classic late infantile neuronal ceroid lipofuscinosis disease-associated mutation, G77R, significantly differed from those revealed by wild-type prosegment in both the mechanism of interaction and the inhibitory rate. This is the first characterization of the inhibitory action of the sedolisin prosegment. Tripeptidyl peptidase I (TPP I)2 is an acidic lysosomal hydrolase sequentially removing tripeptides en bloc from the N terminus of small, unstructured polypeptides (for a review, see Ref.1). The natural substrate(s) of the enzyme still remains elusive. TPP I is widely distributed in the human body, with a high expression level in brain tissue (2, 3). Naturally occurring mutations in TPP I underlie a devastating neurodegenerative disorder of early childhood, classic late infantile neuronal ceroid lipofuscinosis (CLN2) (4).On the basis of significant sequence homology and inhibitory studies, TPP I was assigned to a family of pepstatin-insensitive serine-carboxyl proteases recently renamed sedolisins (for a Like most proteolytic enzymes, TPP I is synthesized as an inactive precursor, zymogen (8, 9). The prepro-TPP I consists of a 19-amino acid (aa) signal peptide cleaved off when the newly forming polypeptide chain is inserted into the endoplasmic reticulum lumen, the 176-aa prosegment (or prodomain), and a 368-aa catalytic domain. As we demonstrated earlier, the removal of the prosegment from a purified TPP I proenzyme (pro-TPP I) occurs via an autocatalytic, intramolecular mechanism, whereby the mature enzyme does not significantly participate in its own generation (10). Efficient in vitro processing and autoactivation of the proenzyme is triggered by lowering the pH of the proenzyme solution to below 4.5. When pro-TPP I is activated at pH 4.5 and above, it is processed slowly and generates additional 6-and 14-aa N-terminal extensions in the newly formed polypeptide, rendering it enzymatically inactive (10). However, as we showed earlier, the presence of polyanionic compounds, such...

Section: Tripeptidyl Peptidase I (Tpp I)mentioning

confidence: 94%

Section: Methodsmentioning

confidence: 99%

Section: Tripeptidyl Peptidase I (Tpp I)mentioning

confidence: 99%

See 1 more Smart Citation

Prosegment of Tripeptidyl Peptidase I Is a Potent, Slow-binding Inhibitor of Its Cognate Enzyme

Golabek

Dolzhanskaya

Walus

et al. 2008

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“…3 This is, to our knowledge, the first report documenting a possible implication of TPP1 in TNF-induced apoptosis. Human TPP1 is a lysosomal serine protease with an acidic pH optimum that cleaves off tripeptides from the free N termini of small polypeptides (68,69). However, its natural substrates are unknown.…”

Section: Discussionmentioning

confidence: 99%

Mannose 6-Phosphorylated Proteins Are Required for Tumor Necrosis Factor-induced Apoptosis

Tardy¹,

Autefage

Garcia

et al. 2004

Whereas caspases are essential components in apoptosis, other proteases seem to be involved in programmed cell death. This study investigated the role of lysosomal mannose 6-phosphorylated proteins in tumor necrosis factor (TNF)-induced apoptosis. We report that fibroblasts isolated from patients affected with inclusion-cell disease (ICD), having a deficient activity of almost all lysosomal hydrolases, are resistant to the toxic effect of TNF. These mutant cells exhibited a defect in TNF-induced caspase activation, Bid cleavage, and release of cytochrome c. In contrast, TNF-induced p42/ p44 MAPK activation and CD54 expression remained unaltered. Human ICD lymphoblasts and fibroblasts derived from mice nullizygous for Igf2 and the two mannose 6-phosphate (M6P) receptors, Mpr300 and Mpr46, which develop an ICD-like phenotype, were also resistant to CD95 ligand and TNF, respectively. Moreover, correction of the lysosomal enzyme defect of ICD fibroblasts, using a medium enriched in M6P-containing proteins, enabled restoration of sensitivity to TNF. This effect was blocked by exogenous M6P but not by cathepsin B or L inhibitors. Altogether, these findings suggest that some M6P-bearing glycoproteins modulate the susceptibility to TNF-induced apoptosis. As a matter of fact, exogenous tripeptidyl peptidase 1, a lysosomal carboxypeptidase, could sensitize ICD fibroblasts to TNF. These observations highlight the hitherto unrecognized role of some mannose 6-phosphorylated proteins such as tripeptidyl peptidase 1 in the apoptotic cascade triggered by TNF.

“…Human TPP I cDNA encodes a preproenzyme of 563 amino acid residues, which includes a 19-amino acid signal peptide cleaved off cotranslationally, a 176-amino acid prodomain removed during the maturation process, and a mature enzyme of 368 amino acid residues (7,(21)(22)(23). The enzyme utilizes in vivo all five potential N-glycosylation sites, and N-glycans ensure proper folding, stability, and transport of TPP I to lysosomes (24).…”

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confidence: 99%

Glycosaminoglycans Modulate Activation, Activity, and Stability of Tripeptidyl-peptidase I in Vitro and in Vivo

Golabek

Walus

Wisniewski

et al. 2005

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Tripeptidyl-peptidase I (TPP I, CLN2 protein) is a lysosomal exopeptidase that sequentially removes tripeptides from the N termini of polypeptides and shows a minor endoprotease activity. Mutations in TPP I lead to classic late-infantile neuronal ceroid lipofuscinosis, a neurodegenerative lysosomal storage disease. TPP I proenzyme is converted in lysosomes into a mature enzyme with the assistance of another protease and is able to autoactivate in acidic pH in vitro via a unimolecular mechanism. Because autoactivation in vitro at the pH values reported for lysosomes generated inactive enzyme, we intended to determine whether physiologically relevant factors can modify this process to also make it plausible in vivo. Here, we report that high ionic strength and glycosaminoglycans (GAGs) increase yields (ionic strength) or yields and rates (GAGs) of activation, enhance degradation of liberated TPP I prosegment fragments, and switch effective autoactivation of TPP I proenzyme toward less acidic pH values (up to pH 6.0). Although ionic strength and GAGs also inhibited TPP I activity in vitro and in living cells, the degree of inhibition (from 20 to 60%) appears to be of rather limited functional significance. Importantly, binding to GAGs improved thermal stability of TPP I and protected the enzyme against alkaline pH-induced denaturation in vitro (t1 ⁄2 of mature enzyme at pH 7.4 increased by ϳ8-fold in the presence of heparin) and in vivo (ϳ2-fold higher loss of TPP I in cells deficient in GAGs than in control cells after bafilomycin A1 treatment). These findings elucidate a potent physiologically relevant mechanism of TPP I regulation by GAGs and suggest that generation of the active enzyme via autoactivation can be accomplished not only in vitro but in vivo as well.